A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include gold, iron, copper, carbon, silicon, mercury, sodium, calcium, hydrogen, nitrogen, chlorine, and neon.

As of May 2011, 118 elements have been identified, the latest being ununoctium in 2002. Of the 118 known elements, only the first 94 are believed to occur naturally on Earth. Of these naturally occurring elements, 80 are stable or essentially so, while the others are radioactive, decaying into other, lighter elements over various timescales from hours to billions of years. Additional elements, of higher atomic numbers than those naturally occurring, have been produced technologically in recent decades as the products of nuclear reactions.

The properties of the chemical elements are often summarized using the periodic table that organizes the elements by increasing atomic number into rows ("periods") in which the columns ("groups") share recurring ("periodic") physical and chemical properties. Its invention is generally credited to Russian chemist Dmitri Mendeleev in 1869.

The universe's naturally occurring chemical elements are thought to have been produced by various cosmic processes, including hydrogen and helium creation during the Big Bang, production of elements as heavy as iron by stellar nucleosynthesis and cosmic-ray spallation, and formation of many heavier elements in supernovae and other cataclysmic cosmic events. While most elements are generally viewed as stable, transformation of one element to another occurs through decay of radioactive elements as well as other nuclear processes such as cosmic ray bombardment and natural nuclear fission of the nuclei of various heavy elements.

When two distinct elements are chemically combined, with the atoms held together by chemical bonds, the result is termed a chemical compound. Chemical compounds may be composed of elements combined in exact whole-number ratios of atoms, as in water, table salt, and such minerals as quartz, calcite, and some metal ores. However, chemical bonding of many types of elements may result in the formation of crystalline solids and metallic alloys for which exact chemical formulas do not exist. Most of the solid substance of the Earth is of this latter type: the atoms that are present in the substance of the Earth's crust, mantle, and inner core are combined into chemical compounds of many compositions, but these do not have precise empirical formulas.

While all of the 94 naturally occurring elements have been identified in mineral samples from the Earth's crust, only a few elements are found occasionally on Earth as recognizable, relative pure minerals. Among the more common of such "native elements" are copper, silver, gold, carbon (as coal, graphite, or diamonds), sulfur, and mercury. Air is primarily a mixture of gaseous elements, with nitrogen, oxygen, and argon being most abundant. Most of the various elements on Earth are present instead in various mixtures, alloys, and chemical compounds in which the physical and chemical properties of the individual elements are not apparent.

Hydrogen and helium are by far the most abundant elements in the universe. However, oxygen is the most abundant element in the Earth's crust, making up almost half of its mass. Although all known chemical matter is composed of these various elements, chemical matter itself constitutes only about 15% of the total matter in the universe. The remainder is dark matter, which is not believed to consist of chemical elements as we know them since it does not contain protons, neutrons or electrons.

The history of discovery of the chemical elements began with the numerous primitive human societies that found such native elements as copper and gold, and extracted (smelted) iron and a few other metallic elements from their ores. Alchemists and chemists subsequently identified and characterized many more, with nearly all of the naturally occurring elements known by 1900.

Many of the elements, alone or in various combined forms, are essential to various kinds of biological life, with carbon, hydrogen, nitrogen, oxygen, phosphorus, potassium, sodium, and sulfur among the most important. Certain kinds of organisms require particular additional elements, for example the magnesium in chlorophyll in green plants, the calcium in mollusc shells, or the iron in the hemoglobin in vertebrate animals' red blood cells. Humans require recurrent consumption of small or trace amounts of dozens of elements, often included in vitamin and mineral supplements.

In human society, almost every element has at least one unique household, commercial, industrial, scientific, or medical use, either in its pure forms or in various chemical compounds, mixtures, alloys, and other substances. Nearly all of the elements through uranium, and also americium, are now available industrially, most to high degrees of purity, except for a few radioactive ones that exist only transiently.

Description

The lightest of the chemical elements are hydrogen and helium, both created by Big Bang nucleosynthesis during the first 20 minutes of the universe in a ratio of around 3:1 by mass (approximately 12:1 by number of atoms). Almost all other elements found in nature, including some further hydrogen and helium created since then, were made by various natural or (at times) artificial methods of nucleosynthesis. On Earth, small amounts of new atoms are naturally produced in nucleogenic reactions, or in cosmogenic processes, such as cosmic ray spallation. New atoms are also naturally produced on Earth as radiogenic daughter isotopes of ongoing radioactive decay processes such as alpha decay, beta decay, spontaneous fission, cluster decay, and other rarer modes of decay.

Of the 94 naturally occurring elements, those with atomic numbers 1 through 40 are all considered to be stable isotopes. Elements with atomic numbers 41 through 82 are apparently stable (except technetium and promethium) but theoretically unstable, or radioactive. The half-lives of elements 41 through 82 are so long however that their radioactive decay has yet to be detected by experiment. These "theoretical radionuclides" have half-lives at least 100 million times longer than the estimated age of the universe. Elements with atomic numbers 83 through 94 are unstable to the point that their radioactive decay can be detected. Some of these elements, notably thorium (atomic number 90) and uranium (atomic number 92), have one or more isotopes with half-lives long enough to survive as remnants of the explosive stellar nucleosynthesis that produced the heavy elements before the formation of our solar system. For example, at over 1.9 years, over a billion times longer than the current estimated age of the universe, bismuth-209 (atomic number 83) has the longest known alpha decay half-life of any naturally occurring element. The very heaviest elements (those beyond plutonium, atomic number 94) undergo radioactive decay with half-lives so short that they have only been observed as the result of experimental observation.

As of 2010, there are 118 known elements (in this context, "known" means observed well enough, even from just a few decay products, to have been differentiated from any other element). Of these 118 elements, 94 occur naturally on Earth. Six of these occur in extreme trace quantities: technetium, atomic number 43; promethium, number 61; astatine, number 85; francium, number 87; neptunium, number 93; and plutonium, number 94. These 94 elements, and also possibly element 98 californium, have been detected in the universe at large, in the spectra of stars and also supernovae, where short-lived radioactive elements are newly being made. The first 94 elements have been detected directly on Earth as naturally-occurring fission or transmutation products of uranium and thorium. Some californium may be present on Earth, but at present, natural californium is only known from supernovae spectra and even there its presence is uncertain (see californium for detail).

The remaining 24 heavier elements, not found today either on Earth or in astronomical spectra, have been derived artificially. All of the heavy elements that are derived solely through artificial means are radioactive, with very short half-lives; if any atoms of these elements were present at the formation of Earth, they are extremely likely to have already decayed, and if present in novae, have been in quantities too small to have been noted. Technetium was the first purportedly non-naturally occurring element to be synthesized, in 1937, although trace amounts of technetium have since been found in nature (and also the element may have been discovered naturally in 1925). This pattern of artificial production and later natural discovery has been repeated with several other radioactive, naturally-occurring rare elements.

Lists of the elements are available by name, by symbol, by atomic number, by density, by melting point, and by boiling point as well as Ionization energies of the elements. The nuclides of stable and radioactive elements are also available as a list of nuclides, sorted by length of half-life for those that are unstable. One of the most convenient, and certainly the most traditional presentation of the elements, is in form of periodic table, which groups elements with similar chemical properties (and usually also similar electronic structures) together.

Atomic number

The atomic number of an element, ''Z'', is equal to the number of protons that defines the element. For example, all carbon atoms contain 6 protons in their nucleus; so the atomic number "Z" of carbon is 6. Carbon atoms may have different numbers of neutrons; atoms of the same element having different numbers of neutrons are known as isotopes of the element.

The number of protons in the atomic nucleus also determines its electric charge, which in turn determines the number of electrons of the atom in its non-ionized state. The electrons are placed into atomic orbitals which determine the atom's various chemical properties. The number of neutrons in a nucleus usually has very little effect on an elements' chemical properties (except in the case of hydrogen and deuterium). Thus, all carbon isotopes have nearly identical chemical properties because they all have six protons and six electrons, even though carbon atoms may differ in number of neutrons. It is for this reason that atomic number rather than mass number (or atomic weight) is considered the identifying characteristic of a chemical element.

Atomic mass

The mass number of an element, ''A'', is the number of nucleons (protons and neutrons) in the atomic nucleus. Different isotopes of a given element are distinguished by their mass numbers, which are conventionally written as a super-index on the left hand side of the atomic symbol (e.g., ²³⁸U).

The relative atomic mass of an element is the average of the atomic masses of all the chemical element's isotopes as found in a particular environment, weighted by isotopic abundance, relative to the atomic mass unit (u). This number may be a fraction that is not close to a whole number, due to the averaging process. On the other hand, the atomic mass of a pure isotope is quite close to its mass number. Whereas the mass number is a natural (or whole) number, the atomic mass of a single isotope is a real number that is close to a natural number. In general, it differs slightly from the mass number as the mass of the protons and neutrons is not exactly 1 u, the electrons also contribute slightly to the atomic mass, and because of the nuclear binding energy. For example, the mass of ¹⁹F is 18.9984032 u. The only exception to the atomic mass of an isotope not being a natural number is ¹²C, which has a mass of exactly 12, because u is ''defined'' as 1/12 of the mass of a free neutral carbon-12 atom in the ground state.

Isotopes

Isotopes are atoms of the same element (that is, with the same number of protons in their atomic nucleus), but having ''different'' numbers of neutrons. Most (66 of 94) naturally occurring elements have more than one stable isotope. Thus, for example, there are three main isotopes of carbon. All carbon atoms have 6 protons in the nucleus, but they can have either 6, 7, or 8 neutrons. Since the mass numbers of these are 12, 13 and 14 respectively, the three isotopes of carbon are known as carbon-12, carbon-13, and carbon-14, often abbreviated to ¹²C, ¹³C, and ¹⁴C. Carbon in everyday life and in chemistry is a mixture of ¹²C, ¹³C, and ¹⁴C atoms.

Except in the case of the isotopes of hydrogen (which differ greatly from each other in relative mass—enough to cause chemical effects), the isotopes of the various elements are typically chemically nearly indistinguishable from each other. For example, the three naturally occurring isotopes of carbon have essentially the same chemical properties, but different nuclear properties. In this example, carbon-12 and carbon-13 are stable atoms, but carbon-14 is unstable; it is radioactive, undergoing beta decay into nitrogen-14.

As illustrated by carbon, all of the elements have some isotopes that are radioactive (radioisotopes), which decay into other elements upon radiating an alpha or beta particle. Certain elements ''only'' have radioactive isotopes: specifically the elements without any stable isotopes are technetium (atomic number 43), promethium (atomic number 61), and all observed elements with atomic numbers greater than 82.

Of the 80 elements with at least one stable isotope, 26 have only one stable isotope, and the mean number of stable isotopes for the 80 stable elements is 3.1 stable isotopes per element. The largest number of stable isotopes that occur for an element is 10 (for tin, element 50).

Allotropes

Atoms of pure elements may bond to each other chemically in more than one way, allowing the pure element to exist in multiple structures (spacial arrangements of atoms), known as allotropes, which differ in their properties. For example, carbon can be found as diamond, which has a tetrahedral structure around each carbon atom; graphite, which has layers of carbon atoms with a hexagonal structure stacked on top of each other; graphene, which is a single layer of graphite that is incredibly strong; fullerenes, which have nearly spherical shapes; and carbon nanotubes, which are tubes with a hexagonal structure (even these may differ from each other in electrical properties). The ability for an element to exist in one of many structural forms is known as 'allotropy'.

The standard state, or reference state, of an element is defined as its thermodynamically most stable state at 1 bar at a given temperature (typically at 298.15 K). In thermochemistry, an element is defined to have an enthalpy of formation of zero in its standard state. For example, the reference state for carbon is graphite, because it is more stable than the other allotropes.

Properties

Several kinds of descriptive categorizations can be applied broadly to the elements, including consideration of their general physical and chemical properties, their states of matter under familiar conditions, their melting and boiling points, their densities, their crystal structures as solids, and their origins.

General properties

Several terms are commonly used to characterize the general physical and chemical properties of the chemical elements. A first distinction is between the metals, which readily conduct electricity, and the nonmetals, which do not, with a small group (the ''metalloids'') having intermediate properties, often behaving as semiconductors.

A more refined classification is often shown in colored presentations of the periodic table; this system restricts the terms "metal" and "nonmetal" to only certain of the more broadly defined metals and nonmetals, adding additional terms for certain sets of the more broadly viewed metals and nonmetals. The version of this classification used in the periodic tables presented here includes: actinides, alkali metals, alkaline earth metals, halogens, lanthanides, metals (or "other metals"), metalloids, noble gases, nonmetals (or "other nonmetals"), and transition metals. In this system, the alkali metals, alkaline earth metals, and transition metals, as well as the lanthanides and the actinides, are special groups of the metals viewed in a broader sense. Similarly, the halogens and the noble gases are nonmetals, viewed in the broader sense. In some presentations, the halogens are not distinguished, with astatine identified as a metalloid and the others identified as nonmetals.

States of matter

Another commonly used basic distinction among the elements is their state of matter (phase), solid, liquid, or gas, at a selected standard temperature and pressure (STP). Most of the elements are solids at conventional temperatures and atmospheric pressure, while several are gases. Only bromine and mercury are liquids at 0 degrees Celsius (32 degrees Fahrenheit) and normal atmospheric pressure; caesium and gallium are solids at that temperature, but melt at 28.4 °C (83.2 °F) and 29.8 °C (85.6 °F), respectively.

Melting and boiling points

Melting and boiling points, typically expressed in degrees Celsius at a pressure of one atmosphere, are commonly used in characterizing the various elements. While known for most elements, either or both of these measurements is still undetermined for some of the radioactive elements available in only tiny quantities. Since helium remains a liquid even at absolute zero at atmospheric pressure, it has only a boiling point, and not a melting point, in conventional presentations.

Densities

The density at a selected standard temperature and pressure (STP) is frequently used in characterizing the elements. Density is often expressed in grams per cubic centimeter (g/cm³). Since several elements are gases at commonly encountered temperatures, their densities are usually stated for their gaseous forms; when liquefied or solidified, the gaseous elements have densities similar to those of the other elements.

When an element has allotropes with different densities, one representative allotrope is typically selected in summary presentations, while densities for each allotrope can be stated where more detail is provided. For example, the three familiar allotropes of carbon (amorphous carbon, graphite, and diamond) have densities of 1.8–2.1, 2.267, and 3.515 g/cm³ respectively.

Crystal structures

The elements studied to date as solid samples have eight kinds of crystal structures: cubic, body-centered cubic, face-centered cubic, hexagonal, monoclinic, orthorhombic, rhombohedral, and tetragonal. For some of the synthetically produced transuranic elements, available samples have been too small to determine crystal structures.

Origins

The elements may also be categorized by their origins, with the first 94 considered naturally occurring, and those with atomic numbers beyond 94 being synthetic (produced technologically, but not known to occur naturally). Of the naturally occurring elements, 84 are considered primordial, either stable or long-persisting, and the remaining 10 transient, produced either recurrently or incidentally as decay products or through other nuclear processes, but not themselves long-persisting. The 91 regularly occurring natural elements include the 80 stable or essentially stable, primordial elements (from hydrogen through lead, omitting technetium and promethium); bismuth, thorium, uranium, and plutonium (radioactive but still remaining from primordial times); and the 7 transiently existing but recurrently produced decay products of thorium, uranium, and plutonium (polonium, astatine, radon, francium, radium, actinium, and protactinium). Three additional naturally occurring elements, technetium, promethium, and neptunium, are only incidentally occurring, present in natural materials only as transiently existing atoms produced from uranium or other heavy elements by rare nuclear processes. Note that helium is recurrently produced naturally from radioactive decay, but little if any primordial helium still exists at the Earth's surface, since this light gas readily escapes from the atmosphere into outer space.

The periodic table

The properties of the chemical elements are often summarized using the periodic table, which powerfully and elegantly organizes the elements by increasing atomic number into rows ("periods") in which the columns ("groups") share recurring ("periodic") physical and chemical properties. The current standard table contains 118 confirmed elements as of April 10, 2010.

Although earlier precursors to this presentation exist, its invention is generally credited to Russian chemist Dmitri Mendeleev in 1869, who intended the table to illustrate recurring trends in the properties of the elements. The layout of the table has been refined and extended over time, as new elements have been discovered, and new theoretical models have been developed to explain chemical behavior.

Use of the periodic table is now ubiquitous within the academic discipline of chemistry, providing an extremely useful framework to classify, systematize and compare all the many different forms of chemical behavior. The table has also found wide application in physics, geology, biology, materials science, engineering, agriculture, medicine, nutrition, environmental health, and astronomy. Its principles are especially important in chemical engineering.

Nomenclature and symbols

The various chemical elements are formally identified by their unique atomic numbers, by their accepted names, and by their symbols.

Atomic numbers

The known elements have atomic numbers from 1 through 118, conventionally presented as Arabic numerals.

Since the elements can be uniquely sequenced by atomic number, conventionally from lowest to hightest (as in a periodic table), sets of elements are sometimes specified by such notation as "through", "beyond", or "from ... through", as in "through iron", "beyond uranium", or "from lanthanum through lutetium". The terms "light" and "heavy" are sometimes also used informally to indicate relative atomic numbers (not densities!), as in "lighter than carbon" or "heavier than lead", although technically the weight or mass of atoms of an element (their atomic weights or atomic masses) do not always increase monotonically with their atomic numbers.

Element names

The naming of various substances now known as elements precedes the atomic theory of matter, as names were given locally by various cultures to various minerals, metals, compounds, alloys, mixtures, and other materials, although at the time it was not known which chemicals were elements and which compounds. As they were identified as elements, the existing names for anciently-known elements (''e.g.,'' gold, mercury, iron) were kept in most countries. National differences emerged over the names of elements either for convenience, linguistic niceties, or nationalism. For a few illustrative examples: German speakers use "Wasserstoff" (water substance) for "hydrogen", "Sauerstoff" (acid substance) for "oxygen" and "Stickstoff" (smothering substance) for "nitrogen", while English and some romance languages use "sodium" for "natrium" and "potassium" for "kalium", and the French, Italians, Greeks, Portuguese and Poles prefer "azote/azot/azoto" (from roots meaning "no life") for "nitrogen".

For purposes of international communication and trade, the official names of the chemical elements both ancient and more recently recognized are decided by the International Union of Pure and Applied Chemistry (IUPAC), which has decided on a sort of international English language, drawing on traditional English names even when an element's chemical symbol is based on a Latin or other traditional word, for example adopting "gold" rather than "aurum" as the name for the 79th element (Au). IUPAC prefers the British spellings "aluminium" and "caesium" over the U.S. spellings "aluminum" and "cesium", and the U.S. "sulfur" over the British "sulphur". However, elements that are practical to sell in bulk in many countries often still have locally used national names, and countries whose national language does not use the Latin alphabet are likely to use the IUPAC element names.

According to IUPAC, chemical elements are not proper nouns in English; consequently, the full name of an element is not routinely capitalized in English, even if derived from a proper noun, as in californium and einsteinium. Isotope names of chemical elements are also uncapitalized if written out, ''e.g.,'' carbon-12 or uranium-235.

In the second half of the twentieth century, physics laboratories became able to produce nuclei of chemical elements with half-lives too short for an appreciable amount of them to exist at any time. These are also named by IUPAC, which generally adopts the name chosen by the discoverer. This practice can lead to the controversial question of which research group actually discovered an element, a question that has delayed naming of elements with atomic number of 104 and higher for a considerable time. (See element naming controversy).

Precursors of such controversies involved the nationalistic namings of elements in the late 19th century. For example, ''lutetium'' was named in reference to Paris, France. The Germans were reluctant to relinquish naming rights to the French, often calling it ''cassiopeium''. Similarly, the British discoverer of ''niobium'' originally named it ''columbium,'' in reference to the New World. It was used extensively as such by American publications prior to international standardization.

Chemical symbols

Specific chemical elements

Before chemistry became a science, alchemists had designed arcane symbols for both metals and common compounds. These were however used as abbreviations in diagrams or procedures; there was no concept of atoms combining to form molecules. With his advances in the atomic theory of matter, John Dalton devised his own simpler symbols, based on circles, which were to be used to depict molecules.

The current system of chemical notation was invented by Berzelius. In this typographical system chemical symbols are not used as mere abbreviations – though each consists of letters of the Latin alphabet – they are symbols intended to be used by peoples of all languages and alphabets. The first of these symbols were intended to be fully universal; since Latin was the common language of science at that time, they were abbreviations based on the Latin names of metals – Cu comes from Cuprum, Fe comes from Ferrum, Ag from Argentum. The symbols were not followed by a period (full stop) as abbreviations were. Later chemical elements were also assigned unique chemical symbols, based on the name of the element, but not necessarily in English. For example, sodium has the chemical symbol 'Na' after the Latin ''natrium''. The same applies to "W" (wolfram) for tungsten, "Fe" (ferrum) for Iron, "Hg" (hydrargyrum) for mercury, "Sn" (stannum) for tin, "K" (kalium) for potassium, "Au" (aurum) for gold, "Ag" (argentum) for silver, "Pb" (plumbum) for lead, "Cu" (Cuprum) for Copper, and "Sb" (stibium) for antimony.

Chemical symbols are understood internationally when element names might need to be translated. There are sometimes differences; for example, the Germans have used "J" instead of "I" for iodine, so the character would not be confused with a roman numeral.

The first letter of a chemical symbol is always capitalized, as in the preceding examples, and the subsequent letters, if any, are always lower case (small letters). Thus, the symbols for californium or einsteinium are Cf and Es.

General chemical symbols

There are also symbols for series of chemical elements, for comparative formulas. These are one capital letter in length, and the letters are reserved so they are not permitted to be given for the names of specific elements. For example, an "X" is used to indicate a variable group amongst a class of compounds (though usually a halogen), while "R" is used for a radical, meaning a compound structure such as a hydrocarbon chain. The letter "Q" is reserved for "heat" in a chemical reaction. "Y" is also often used as a general chemical symbol, although it is also the symbol of yttrium. "Z" is also frequently used as a general variable group. "L" is used to represent a general ligand in inorganic and organometallic chemistry. "M" is also often used in place of a general metal.

At least one additional, two-letter generic chemical symbol is also in informal usage, "Ln" for any lanthanide element.

Isotope symbols

Isotopes are distinguished by the atomic mass number (total protons and neutrons) for a particular isotope of an element, with this number combined with the pertinent element's symbol. IUPAC prefers that isotope symbols be written in superscript notation when practical, for example ¹²C and ²³⁵U. However, other notations, such as carbon-12 and uranium-235, or C-12 and U-235, are also used.

As a special case, the three naturally occurring isotopes of the element hydrogen are often specified as H for ¹H (protium), D for ²H (deuterium), and T for ³H (tritium). This convention is easier to use in chemical equations, replacing the need to write out the mass number for each atom. For example, the formula for heavy water may be written D₂O instead of ²H₂O.

Origin of the elements

Only about 4% of the total mass of the universe is made of atoms or ions, and thus represented by chemical elements. This fraction is about 15% of the total matter, with the remainder of the matter (85%) being dark matter. The nature of dark matter is unknown, but it is not composed of atoms of chemical elements because it contains no protons, neutrons, or electrons. (The remaining non-matter part of the mass of the universe is composed of the even more mysterious dark energy).

The universe's 94 naturally occurring chemical elements are thought to have been produced by at least four cosmic processes. Most of the hydrogen and helium in the universe was produced primordially in the first few minutes of the Big Bang. Three recurrently occurring later processes are thought to have produced the remaining elements. Stellar nucleosynthesis, an ongoing process, produces all elements from carbon through iron in atomic number, but little lithium, beryllium, or boron. Elements heavier in atomic number than iron, as heavy as uranium and plutonium, are produced by explosive nucleosynthesis in supernovas and other cataclysmic cosmic events. Cosmic ray spallation (fragmentation) of carbon, nitrogen, and oxygen is important to the production of lithium, beryllium and boron.

During the early phases of the Big Bang, nucleosynthesis of hydrogen nuclei resulted in the production of hydrogen-1 (protonium, ¹H) and helium-4 (⁴He), as well as a smaller amount of deuterium (²H) and very minuscule amounts (on the order of 10⁻¹⁰) of lithium and beryllium. Even smaller amounts of boron may have been produced in the Big Bang, since it has been observed in some very old stars, while carbon has not. It is generally agreed that no heavier elements than boron were produced in the Big Bang. As a result, the primordial abundance of atoms (or ions) consisted of roughly 75% ¹H, 25% ⁴He, and 0.01% deuterium, with only tiny traces of lithium, beryllium, and perhaps boron. Subsequent enrichment of galactic halos occurred due to stellar nucleosynthesis and supernova nucleosynthesis. However, the element abundance in intergalactic space can still closely resemble primordial conditions, unless it has been enriched by some means.

On Earth (and elsewhere), trace amounts of various elements continue to be produced from other elements as products of natural transmutation processes. These include some produced by cosmic rays or other nuclear reactions (see cosmogenic and nucleogenic nuclides), and others produced as decay products of long-lived primordial nuclides. For example, trace (but detectable) amounts of carbon-14 (¹⁴C) are continually produced in the atmosphere by cosmic rays impacting nitrogen atoms, and argon-40 (⁴⁰Ar) is continually produced by the decay of primordially occurring but unstable potassium-40 (⁴⁰K). Also, three primordially occurring but radioactive actinides, thorium, uranium, and plutonium, decay through a series of recurrently produced but unstable radioactive elements such as radium and radon, which are transiently present in any sample of these metals or their ores or compounds. Three other radioactive elements, technetium, promethium, and neptunium, occur only incidentally in natural materials, produced as individual atoms by natural fission of the nuclei of various heavy elements or in other rare nuclear processses.

Human technology has produced various additional elements beyond these first 94, with those through atomic number 118 now known.

Abundance

The following graph (note log scale) shows abundance of elements in our solar system. The table shows the twelve most common elements in our galaxy (estimated spectroscopically), as measured in parts per million, by mass. Nearby galaxies that have evolved along similar lines have a corresponding enrichment of elements heavier than hydrogen and helium. The more distant galaxies are being viewed as they appeared in the past, so their abundances of elements appear closer to the primordial mixture. As physical laws and processes appear common throughout the visible universe, however, it is expected that these galaxies will likewise have evolved similar abundances of elements.

{|class="wikitable" |- !Element!!Parts per millionby mass |- |Hydrogen |739,000 |- |Helium |240,000 |- |Oxygen |10,400 |- |Carbon |4,600 |- |Neon |1,340 |- |Iron |1,090 |- |Nitrogen |960 |- |Silicon |650 |- |Magnesium |580 |- |Sulfur |440 |- |Potassium |210 |- |Nickel |100 |}

History

Evolving definitions

The concept of an "element" as an undivisible substance has developed through three major historical phases: Classical definitions (such as those of the ancient Greeks), chemical definitions, and atomic definitions.

Classical definitions

Ancient philosophy posited a set of classical elements to explain observed patterns in nature. These ''elements'' originally referred to ''earth'', ''water'', ''air'' and ''fire'' rather than the chemical elements of modern science.

The term 'elements' (''stoicheia'') was first used by the Greek philosopher Plato in about 360 BCE, in his dialogue Timaeus, which includes a discussion of the composition of inorganic and organic bodies and is a speculative treatise on chemistry. Plato believed the elements introduced a century earlier by Empedocles were composed of small polyhedral ''forms'': tetrahedron (fire), octahedron (air), icosahedron (water), and cube (earth).

Aristotle, c. 350 BCE, also used the term ''stoicheia'' and added a fifth element called ''aether,'' which formed the heavens. Aristotle defined an element as:

Chemical definitions

In 1661, chemist Robert Boyle showed that there were more than just the four classical elements that the ancients had assumed. The first modern list of chemical elements was given in Antoine Lavoisier's 1789 ''Elements of Chemistry'', which contained thirty-three elements, including light and caloric. By 1818, Jöns Jakob Berzelius had determined atomic weights for forty-five of the forty-nine then-accepted accepted elements. Dmitri Mendeleev had sixty-six elements in his periodic table of 1869.

From Boyle until the early 20th century, an element was defined as a pure substance that could not be decomposed into any simpler substance. Put another way, a chemical element cannot be transformed into other chemical elements by chemical processes. Elements during this time were generally distinguished by their atomic weights, a property measurable with fair accuracy by available analytical techniques.

Atomic definitions

The 1913 discovery by Henry Moseley that the nuclear charge is the physical basis for an atom's atomic number, further refined when the nature of protons and neutrons became appreciated, eventually led to the current definition of an element, based on atomic number (number of protons per atomic nucleus). The use of atomic numbers, rather than atomic weights, to distinguish elements has greater predictive value (since these numbers are integers), and also resolves some ambiguities in the chemistry-based view due to varying properties of isotopes and allotropes within the same element. Currently IUPAC defines an element to exist if it has isotopes with a lifetime longer than the 10⁻¹⁴ seconds which takes the nucleus to form an electronic cloud.

By 1914, seventy-two elements were known, all naturally occurring. The remaining naturally occurring elements were discovered or isolated is subsequent decades, and various additional elements have also been produced synthetically, with much of that work pioneered by Glenn T. Seaborg. In 1955, element 101 was discovered and named mendelevium in honor of D.I. Mendeleev, the first to arrange the elements in a periodic manner. Most recently, the synthesis of element 118 was reported in October 2006, and the synthesis of element 117 was reported in April 2010.

Discovery and recognition of various elements

Ten materials familiar to various prehistoric cultures are now known to be chemical elements: Carbon, copper, gold, iron, lead, mercury, silver, sulfur, tin, and zinc. Three additional materials now accepted as elements, arsenic, antimony, and bismuth, were recognized as distinct substances prior to 1500 AD. Phosphorus, cobalt, and platinum were isolated before 1750.

Most of the remaining naturally occurring chemical elements were identified and characterized by 1900, including:

Such now-familiar industrial materials as aluminum, silicon, nickel, chromium, magnesium, and tungsten

Reactive metals such as lithium, sodium, potassium, and calcium

The halogens fluorine, chlorine, bromine, and iodine

Gases such as hydrogen, oxygen, nitrogen, helium, argon, and neon

Most of the rare-earth elements, including cerium, lanthanum, gadolinium, and neodymium, and

The more common radioactive elements, including uranium, thorium, radium, and radon

Elements isolated or produced since 1900 include:

The three remaining undiscovered regularly occurring stable natural elements: hafnium, lutetium, and rhenium

Plutonium, first produced synthetically but now also known from a few long-persisting natural occurrences

The three incidentally occurring natural elements (neptunium, promethium, and technetium), all first produced synthetically but later discovered in trace amounts in certain geological samples

Three scarcer decay products of uranium or thorium (astatine, francium, and protactinium),

Various synthetic transuranic elements, beginning with americium, curium, berkelium, and californium

Recently discovered elements

The first transuranium element (element with atomic number greater than 92) discovered was neptunium in 1940. As of February 2010, only the elements up to 112, copernicium, have been confirmed as discovered by IUPAC, while claims have been made for synthesis of elements 113, 114, 115, 116, 117 and 118. The discovery of element 112 was acknowledged in 2009, and the name 'copernicium' and the atomic symbol 'Cn' were suggested for it. The name and symbol were officially endorsed by IUPAC on February 19, 2010. The heaviest element that is believed to have been synthesized to date is element 118, ununoctium, on October 9, 2006, by the Flerov Laboratory of Nuclear Reactions in Dubna, Russia. Element 117 was the latest element claimed to be discovered, in 2009. IUPAC officially recognized ununquadium and ununhexium, elements 114 and 116, in June 2011.

List of the 118 known chemical elements

The following sortable table includes the 118 known chemical elements, with the names linking to the ''Wikipedia'' articles on each.

Atomic number, name, and symbol all serve independently as unique identifiers.

Names are those accepted by IUPAC; provisional names for recently produced elements not yet formally named are in parentheses.

Group, period, and block refer to an element's position in the periodic table.

State of matter ''(solid, liquid,'' or ''gas)'' applies at standard temperature and pressure conditions (STP).

Occurrence distinguishes naturally occurring elements, categorized as either ''primordial'' or ''transient'' (from decay), and additional ''synthetic'' elements that have been produced technologically, but are not known to occur naturally.

Description summarizes an element's properties using the broad categories commonly presented in periodic tables: ''Actinide, alkali metal, alkaline earth metal, halogen, lanthanide, metal, metalloid, noble gas, non-metal,'' and ''transition metal.''

+ List of elements
Atomic number>Atomic no.	! Name	Chemical symbol>Symbol	Group (periodic table)>Group	Period (periodic table)>Period	Periodic table block>Block	! State of matter	! Occurrence	! Description
1	[[Hydrogen	H	1	1	s	Gas	Primordial	Non-metal
2	Helium	He	18	1	s	Gas	Primordial	Noble gas
3	Lithium	Li	1	2	s	Solid	Primordial	Alkali metal
4	Beryllium	Be	2	2	s	Solid	Primordial	Alkaline earth metal
5	Boron	B	13	2	p	Solid	Primordial	Metalloid
6	Carbon	C	14	2	p	Solid	Primordial	Non-metal
7	Nitrogen	N	15	2	p	Gas	Primordial	Non-metal
8	Oxygen	O	16	2	p	Gas	Primordial	Non-metal
9	Fluorine	F	17	2	p	Gas	Primordial	Halogen
10	Neon	Ne	18	2	p	Gas	Primordial	Noble gas
11	Sodium	Na	1	3	s	Solid	Primordial	Alkali metal
12	Magnesium	Mg	2	3	s	Solid	Primordial	Alkaline earth metal
13	Aluminium	Al	13	3	p	Solid	Primordial	Metal
14	Silicon	Si	14	3	p	Solid	Primordial	Metalloid
15	Phosphorus	P	15	3	p	Solid	Primordial	Non-metal
16	Sulfur	S	16	3	p	Solid	Primordial	Non-metal
17	Chlorine	Cl	17	3	p	Gas	Primordial	Halogen
18	Argon	Ar	18	3	p	Gas	Primordial	Noble gas
19	Potassium	K	1	4	s	Solid	Primordial	Alkali metal
20	Calcium	Ca	2	4	s	Solid	Primordial	Alkaline earth metal
21	Scandium	Sc	3	4	d	Solid	Primordial	Transition metal
22	Titanium	Ti	4	4	d	Solid	Primordial	Transition metal
23	Vanadium	V	5	4	d	Solid	Primordial	Transition metal
24	Chromium	Cr	6	4	d	Solid	Primordial	Transition metal
25	Manganese	Mn	7	4	d	Solid	Primordial	Transition metal
26	Iron	Fe	8	4	d	Solid	Primordial	Transition metal
27	Cobalt	Co	9	4	d	Solid	Primordial	Transition metal
28	Nickel	Ni	10	4	d	Solid	Primordial	Transition metal
29	Copper	Cu	11	4	d	Solid	Primordial	Transition metal
30	Zinc	Zn	12	4	d	Solid	Primordial	Transition metal
31	Gallium	Ga	13	4	p	Solid	Primordial	Metal
32	Germanium	Ge	14	4	p	Solid	Primordial	Metalloid
33	Arsenic	As	15	4	p	Solid	Primordial	Metalloid
34	Selenium	Se	16	4	p	Solid	Primordial	Non-metal
35	Bromine	Br	17	4	p	Liquid	Primordial	Halogen
36	Krypton	Kr	18	4	p	Gas	Primordial	Noble gas
37	Rubidium	Rb	1	5	s	Solid	Primordial	Alkali metal
38	Strontium	Sr	2	5	s	Solid	Primordial	Alkaline earth metal
39	Yttrium	Y	3	5	d	Solid	Primordial	Transition metal
40	Zirconium	Zr	4	5	d	Solid	Primordial	Transition metal
41	Niobium	Nb	5	5	d	Solid	Primordial	Transition metal
42	Molybdenum	Mo	6	5	d	Solid	Primordial	Transition metal
43	Technetium	Tc	7	5	d	Solid	Transient	Transition metal
44	Ruthenium	Ru	8	5	d	Solid	Primordial	Transition metal
45	Rhodium	Rh	9	5	d	Solid	Primordial	Transition metal
46	Palladium	Pd	10	5	d	Solid	Primordial	Transition metal
47	Silver	Ag	11	5	d	Solid	Primordial	Transition metal
48	Cadmium	Cd	12	5	d	Solid	Primordial	Transition metal
49	Indium	In	13	5	p	Solid	Primordial	Metal
50	Tin	Sn	14	5	p	Solid	Primordial	Metal
51	Antimony	Sb	15	5	p	Solid	Primordial	Metalloid
52	Tellurium	Te	16	5	p	Solid	Primordial	Metalloid
53	Iodine	I	17	5	p	Solid	Primordial	Halogen
54	Xenon	Xe	18	5	p	Gas	Primordial	Noble gas
55	Caesium	Cs	1	6	s	Solid	Primordial	Alkali metal
56	Barium	Ba	2	6	s	Solid	Primordial	Alkaline earth metal
57	Lanthanum	La	3	6	f	Solid	Primordial	Lanthanide
58	Cerium	Ce	3	6	f	Solid	Primordial	Lanthanide
59	Praseodymium	Pr	3	6	f	Solid	Primordial	Lanthanide
60	Neodymium	Nd	3	6	f	Solid	Primordial	Lanthanide
61	Promethium	Pm	3	6	f	Solid	Transient	Lanthanide
62	Samarium	Sm	3	6	f	Solid	Primordial	Lanthanide
63	Europium	Eu	3	6	f	Solid	Primordial	Lanthanide
64	Gadolinium	Gd	3	6	f	Solid	Primordial	Lanthanide
65	Terbium	Tb	3	6	f	Solid	Primordial	Lanthanide
66	Dysprosium	Dy	3	6	f	Solid	Primordial	Lanthanide
67	Holmium	Ho	3	6	f	Solid	Primordial	Lanthanide
68	Erbium	Er	3	6	f	Solid	Primordial	Lanthanide
69	Thulium	Tm	3	6	f	Solid	Primordial	Lanthanide
70	Ytterbium	Yb	3	6	f	Solid	Primordial	Lanthanide
71	Lutetium	Lu	3	6	d	Solid	Primordial	Lanthanide
72	Hafnium	Hf	4	6	d	Solid	Primordial	Transition metal
73	Tantalum	Ta	5	6	d	Solid	Primordial	Transition metal
74	Tungsten	W	6	6	d	Solid	Primordial	Transition metal
75	Rhenium	Re	7	6	d	Solid	Primordial	Transition metal
76	Osmium	Os	8	6	d	Solid	Primordial	Transition metal
77	Iridium	Ir	9	6	d	Solid	Primordial	Transition metal
78	Platinum	Pt	10	6	d	Solid	Primordial	Transition metal
79	Gold	Au	11	6	d	Solid	Primordial	Transition metal
80		Hg	12	6	d	Liquid	Primordial	Transition metal
81	Thallium	Tl	13	6	p	Solid	Primordial	Metal
82	Lead	Pb	14	6	p	Solid	Primordial	Metal
83	Bismuth	Bi	15	6	p	Solid	Primordial	Metal
84	Polonium	Po	16	6	p	Solid	Transient	Metalloid
85	Astatine	At	17	6	p	Solid	Transient	Halogen
86	Radon	Rn	18	6	p	Gas	Transient	Noble gas
87	Francium	Fr	1	7	s	Solid	Transient	Alkali metal
88	Radium	Ra	2	7	s	Solid	Transient	Alkaline earth metal
89	Actinium	Ac	3	7	f	Solid	Transient	Actinide
90	Thorium	Th	3	7	f	Solid	Primordial	Actinide
91	Protactinium	Pa	3	7	f	Solid	Transient	Actinide
92	Uranium	U	3	7	f	Solid	Primordial	Actinide
93	Neptunium	Np	3	7	f	Solid	Transient	Actinide
94	Plutonium	Pu	3	7	f	Solid	Primordial	Actinide
95	Americium	Am	3	7	f	Solid	Synthetic	Actinide
96	Curium	Cm	3	7	f	Solid	Synthetic	Actinide
97	Berkelium	Bk	3	7	f	Solid	Synthetic	Actinide
98	Californium	Cf	3	7	f	Solid	Synthetic	Actinide
99	Einsteinium	Es	3	7	f	Solid	Synthetic	Actinide
100	Fermium	Fm	3	7	f	Solid	Synthetic	Actinide
101	Mendelevium	Md	3	7	f	Solid	Synthetic	Actinide
102	Nobelium	No	3	7	f	Solid	Synthetic	Actinide
103	Lawrencium	Lr	3	7	d	Solid	Synthetic	Actinide
104	Rutherfordium	Rf	4	7	d		Synthetic	Transition metal
105	Dubnium	Db	5	7	d		Synthetic	Transition metal
106	Seaborgium	Sg	6	7	d		Synthetic	Transition metal
107	Bohrium	Bh	7	7	d		Synthetic	Transition metal
108	Hassium	Hs	8	7	d		Synthetic	Transition metal
109	Meitnerium	Mt	9	7	d		Synthetic
110	Darmstadtium	Ds	10	7	d		Synthetic
111	Roentgenium	Rg	11	7	d		Synthetic
112	Copernicium	Cn	12	7	d		Synthetic	Transition metal
113	(Ununtrium)	Uut	13	7	p		Synthetic
114	(Ununquadium)	Uuq	14	7	p		Synthetic
115	(Ununpentium)	Uup	15	7	p		Synthetic
116	(Ununhexium)	Uuh	16	7	p		Synthetic
117	(Ununseptium)	Uus	17	7	p		Synthetic
118	(Ununoctium)	Uuo	18	7	p		Synthetic

See also

Compound

Chemistry

Discovery of the chemical elements

Element collecting

Fictional element

Goldschmidt classification

Island of stability

List of elements by name

Systematic element name

Prices of elements and their compounds

Periodic Systems of Small Molecules

Table of nuclides

List of nuclides

References

Further reading

External links

Videos for each element by the University of Nottingham

Category:Chemistry

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name	Carl Sagan
birth date	November 09, 1934
birth place	Brooklyn, New York, U.S.
residence	United States
nationality	United States
death date	December 20, 1996
death place	Seattle, Washington, U.S.
education	Rahway High School
alma mater	University of Chicago,Cornell University
field	Astronomy, astrophysics, cosmology, astrobiology, space science, planetary science
work institutions	Cornell UniversityHarvard UniversitySmithsonian Astrophysical ObservatoryUniversity of California, Berkeley
alma mater	University of Chicago(B.A.), (B.Sc.), (M.Sc.), (PhD)
known for	Search for Extra-Terrestrial Intelligence (SETI)''Cosmos: A Personal Voyage''''Cosmos''Voyager Golden RecordPioneer plaque''Contact''''Pale Blue Dot''
prizes	NASA Distinguished Public Service Medal (1977)Pulitzer Prize for General Non-Fiction (1978)Oersted Medal (1990)National Academy of Sciences Public Welfare Medal (1994) }}

Carl Edward Sagan (; November 9, 1934 – December 20, 1996) was an American astronomer, astrophysicist, cosmologist, author, science popularizer, and science communicator in astronomy and natural sciences. He published more than 600 scientific papers and articles and was author, co-author or editor of more than 20 books. He advocated ''scientifically skeptical inquiry'' and the ''scientific method'', pioneered exobiology and promoted the Search for Extra-Terrestrial Intelligence (SETI).

Sagan is known for his popular science books and for the award-winning 1980 television series ''Cosmos: A Personal Voyage'', which he narrated and co-wrote. The book ''Cosmos'' was published to accompany the series. Sagan wrote the novel ''Contact'', the basis for a 1997 film of the same name.

Early life

Carl Sagan was born in Brooklyn, New York, to a Ukrainian Jewish family. His father, Sam Sagan, was an immigrant garment worker from Kamenets-Podolsk, Ukraine; his mother, Rachel Molly Gruber, a housewife. Carl was named in honor of Rachel's biological mother, Chaiya Clara, in Sagan's words, "the mother she never knew." Sagan graduated from Rahway High School in Rahway, New Jersey, in 1951.

He had a sister, Carol, and the family lived in a modest apartment near the Atlantic Ocean, in Bensonhurst, a Brooklyn neighborhood. According to Sagan, they were Reform Jews, the most liberal of the three main Jewish groups. Both Sagan and his sister agree that their father was not especially religious, but that their mother "definitely believed in God, and was active in the temple ... and served only Kosher meat." During the height of the Depression, his father had to accept a job as a theater usher.

According to biographer Keay Davidson, Sagan's "inner war" was a result of his close relations with both his parents, who were in many ways "opposites." Sagan traced his later analytical urges to his mother, a woman who had known "extreme poverty as a child," and had grown up almost homeless in New York City during World War I and the 1920s. She had her own intellectual ambitions as a young woman, but they were blocked by social restrictions, because of her poverty, her being a woman and wife, and her Jewish ethnicity. Davidson notes that she therefore "worshiped her only son, Carl. He would fulfill her unfulfilled dreams."

However, his "sense of wonder" came from his father, who was a "quiet and soft-hearted escapee from the Czar." In his free time, he gave apples to the poor, or helped soothe labor-management tensions within New York's "tumultuous" garment industry. Although he was "awed" by Carl's "brilliance, his boyish chatter about stars and dinosaurs," he took his son's inquisitiveness in stride, as part of his growing up. In his later years as a writer and scientist, Sagan would often draw on his childhood memories to illustrate scientific points, as he did in his book, ''Shadows of Forgotten Ancestors''. Sagan describes his parents' influence on his later thinking:

:''My parents were not scientists. They knew almost nothing about science. But in introducing me simultaneously to skepticism and to wonder, they taught me the two uneasily cohabiting modes of thought that are central to the scientific method.''

1939 World's Fair

Sagan recalls that one of his best experiences was when he was four or five years old, his parents took him to the 1939 New York World's Fair. The exhibits became a turning point in his life. He later recalled the moving map of the "America of Tomorrow" exhibit: "It showed beautiful highways and cloverleaves and little General Motors cars all carrying people to skyscrapers, buildings with lovely spires, flying buttresses—and it looked great!" At other exhibits, he remembered how a flashlight that shined on a photoelectric cell created a cracking sound, and how the sound from a tuning fork became a wave on an oscilloscope. He also witnessed the future media technology that would replace radio: television. Sagan wrote:

:''Plainly, the world held wonders of a kind I had never guessed. How could a tone become a picture and light become a noise?''

He also saw one of the Fair's most publicized events, the burial of a time capsule at Flushing Meadows, which contained mementos of the 1930s to be recovered by Earth's descendants in a future millennium. "The time capsule thrilled Carl," writes Davidson. As an adult, Sagan and his colleagues created similar time capsules, but ones that would be sent out into the galaxy. These were the Pioneer plaque and the ''Voyager Golden Record'' records, all of which were spinoffs of Sagan's memories of the World Fair.

World War II

During World War II, Sagan's family worried about the fate of their European relatives. Sagan, however, was generally unaware of the details of the ongoing war. He writes, "Sure, we had relatives who were caught up in the Holocaust. Hitler was not a popular fellow in our household ... But on the other hand, I was fairly insulated from the horrors of the war." His sister, Carol, said that their mother "above all wanted to protect Carl ... She had an extraordinarily difficult time dealing with World War II and the Holocaust." Sagan's book, ''The Demon-Haunted World'' (1996), included his memories of this conflicted period, when his family dealt with the realities of the war in Europe, but tried to prevent it from undermining his optimistic spirit.

Inquisitiveness about nature

Soon after entering elementary school, he began to express a strong inquisitiveness about nature. Sagan recalled taking his first trips to the public library alone, at the age of five, when his mother got him a library card. He wanted to learn what stars were, since none of his friends or their parents could give him a clear answer: :''I went to the librarian and asked for a book about stars ... And the answer was stunning. It was that the Sun was a star but really close. The stars were suns, but so far away they were just little points of light ... The scale of the universe suddenly opened up to me. It was a kind of religious experience. There was a magnificence to it, a grandeur, a scale which has never left me. Never ever left me.''

About the time he was six or seven, he and a close friend took trips to the American Museum of Natural History in New York City. While there, they went to the Hayden Planetarium and walked around the museum's exhibits of space objects, such as meteorites, and displays of dinosaurs and animals in natural settings. Sagan writes about those visits: :''I was transfixed by the dioramas—lifelike representations of animals and their habitats all over the world. Penguins on the dimly lit Antarctic ice; ... a family of gorillas, the male beating his chest, ... an American grizzly bear standing on his hind legs, ten or twelve feet tall, and staring me right in the eye.''

His parents helped nurture his growing interest in science by buying him chemistry sets and reading materials. His interest in space, however, was his primary focus, especially after reading science fiction stories by writers such as Edgar Rice Burroughs, which stirred his imagination about life on other planets, such as Mars. According to biographer Ray Spangenburg, these early years as Sagan tried to understand the mysteries of the planets, became a "driving force in his life, a continual spark to his intellect, and a quest that would never be forgotten."

Education and scientific career

He attended the University of Chicago, where he participated in the Ryerson Astronomical Society, received a bachelor of arts in self-proclaimed "nothing" with general and special honors in 1954, a bachelor of science in physics in 1955, and a master of science in physics in 1956 before earning a PhD in astronomy and astrophysics in 1960. During his time as an honors program undergraduate, Sagan worked in the laboratory of the geneticist H. J. Muller and wrote a thesis on the origins of life with physical chemist H.C. Urey. From 1960 to 1962 Sagan was a Miller Fellow at the University of California, Berkeley. From 1962 to 1968, he worked at the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts.

Sagan lectured and did research at Harvard University until 1968, when he moved to Cornell University in Ithaca, New York. He became a full Professor at Cornell in 1971, and he directed the Laboratory for Planetary Studies there. From 1972 to 1981, Sagan was the Associate Director of the Center for Radio Physics and Space Research at Cornell.

Sagan was associated with the US space program from its inception. From the 1950s onward, he worked as an advisor to NASA, where one of his duties included briefing the Apollo astronauts before their flights to the Moon. Sagan contributed to many of the robotic spacecraft missions that explored the solar system, arranging experiments on many of the expeditions. He conceived the idea of adding an unalterable and universal message on spacecraft destined to leave the solar system that could potentially be understood by any extraterrestrial intelligence that might find it. Sagan assembled the first physical message that was sent into space: a gold- anodized plaque, attached to the space probe Pioneer 10, launched in 1972. Pioneer 11, also carrying another copy of the plaque, was launched the following year. He continued to refine his designs; the most elaborate message he helped to develop and assemble was the Voyager Golden Record that was sent out with the Voyager space probes in 1977. Sagan often challenged the decisions to fund the Space Shuttle and Space Station at the expense of further robotic missions.

Sagan taught a course on critical thinking at Cornell University until he died in 1996 from pneumonia, a few months after finding that he was in remission of myelodysplastic syndrome.

Scientific achievements

Sagan's contributions were central to the discovery of the high surface temperatures of the planet Venus. In the early 1960s no one knew for certain the basic conditions of that planet's surface, and Sagan listed the possibilities in a report later depicted for popularization in a Time-Life book, ''Planets''. His own view was that Venus was dry and very hot as opposed to the balmy paradise others had imagined. He had investigated radio emissions from Venus and concluded that there was a surface temperature of . As a visiting scientist to NASA's Jet Propulsion Laboratory, he contributed to the first Mariner missions to Venus, working on the design and management of the project. Mariner 2 confirmed his conclusions on the surface conditions of Venus in 1962.

Sagan was among the first to hypothesize that Saturn's moon Titan might possess oceans of liquid compounds on its surface and that Jupiter's moon Europa might possess subsurface oceans of water. This would make Europa potentially habitable for life. Europa's subsurface ocean of water was later indirectly confirmed by the spacecraft Galileo. The mystery of Titan's reddish haze was also solved with Sagan's help. The reddish haze was revealed to be due to complex organic molecules constantly raining down onto Titan's surface.

He further contributed insights regarding the atmospheres of Venus and Jupiter as well as seasonal changes on Mars. Sagan established that the atmosphere of Venus is extremely hot and dense with pressures increasing steadily all the way down to the surface. He also perceived global warming as a growing, man-made danger and likened it to the natural development of Venus into a hot, life-hostile planet through a kind of runaway greenhouse effect. Sagan and his Cornell colleague Edwin Ernest Salpeter speculated about life in Jupiter's clouds, given the planet's dense atmospheric composition rich in organic molecules. He studied the observed color variations on Mars' surface and concluded that they were not seasonal or vegetational changes as most believed but shifts in surface dust caused by windstorms.

Sagan is best known, however, for his research on the possibilities of extraterrestrial life, including experimental demonstration of the production of amino acids from basic chemicals by radiation.

He is also the 1994 recipient of the Public Welfare Medal, the highest award of the National Academy of Sciences for "distinguished contributions in the application of science to the public welfare." He was denied membership in the Academy, reportedly because his media activities made him unpopular with many other scientists.

Scientific advocacy

Sagan's ability to convey his ideas allowed many people to better understand the cosmos—simultaneously emphasizing the value and worthiness of the human race, and the relative insignificance of the Earth in comparison to the universe. He delivered the 1977 series of Royal Institution Christmas Lectures in London. He hosted and, with Ann Druyan, co-wrote and co-produced the highly popular thirteen-part PBS television series ''Cosmos: A Personal Voyage'' modeled on Jacob Bronowski's ''The Ascent of Man''.

''Cosmos'' covered a wide range of scientific subjects including the origin of life and a perspective of our place in the universe. The series was first broadcast by the Public Broadcasting Service in 1980, winning an Emmy and a Peabody Award. It has been broadcast in more than 60 countries and seen by over 500 million people, making it the most widely watched PBS program in history. In addition, ''Time'' magazine ran a cover story about Sagan soon after the show broadcast, referring to him as "creator, chief writer and host-narrator of the new public television series Cosmos, [and] takes the controls of his fantasy spaceship."

Sagan was a proponent of the search for extraterrestrial life. He urged the scientific community to listen with radio telescopes for signals from potential intelligent extraterrestrial life-forms. Sagan was so persuasive that by 1982 he was able to get a petition advocating SETI published in the journal ''Science'' and signed by 70 scientists including seven Nobel Prize winners. This was a tremendous increase in the respectability of this controversial field. Sagan also helped Dr. Frank Drake write the Arecibo message, a radio message beamed into space from the Arecibo radio telescope on November 16, 1974, aimed at informing potential extraterrestrials about Earth.

Sagan was chief technology officer of the professional planetary research journal ''Icarus'' for twelve years. He co-founded the ''Planetary Society'', the largest space-interest group in the world, with over 100,000 members in more than 149 countries, and was a member of the SETI Institute Board of Trustees. Sagan served as Chairman of the Division for Planetary Science of the American Astronomical Society, as President of the Planetology Section of the American Geophysical Union, and as Chairman of the Astronomy Section of the American Association for the Advancement of Science.

At the height of the Cold War, Sagan became involved in public awareness efforts for the effects of nuclear war when a mathematical climate model suggested that a substantial nuclear exchange could upset the delicate balance of life on Earth. He was one of five authors—the "S" of the "TTAPS" report as the research paper came to be known. He eventually co-authored the scientific paper hypothesizing a global nuclear winter following nuclear war. He also co-authored the book ''A Path Where No Man Thought: Nuclear Winter and the End of the Arms Race'', a comprehensive examination of the phenomenon of nuclear winter.

Sagan also wrote books to popularize science which reflected and expanded upon some of the themes of ''A Personal Voyage'', and became the best-selling science book ever published in English; ''The Dragons of Eden: Speculations on the Evolution of Human Intelligence'', which won a Pulitzer Prize; and ''Broca's Brain: Reflections on the Romance of Science''. Sagan also wrote the best-selling science fiction novel ''Contact'' in 1985, based on a film treatment he wrote with his wife in 1979, but he did not live to see the book's 1997 motion picture adaptation, which starred Jodie Foster and won the 1998 Hugo Award for Best Dramatic Adaption.

thumb|left|Pale Blue Dot: Earth is a bright pixel when photographed from "Voyager 1" six billion kilometers out (past Pluto). Sagan encouraged NASA to generate this image. He wrote a sequel to ''Cosmos,'' ''Pale Blue Dot: A Vision of the Human Future in Space'', which was selected as a notable book of 1995 by ''The New York Times''. He appeared on PBS' Charlie Rose program in January 1995. Sagan also wrote an introduction for the bestselling book by Stephen Hawking, ''A Brief History of Time''. Sagan was also known for his popularization of science, his efforts to increase scientific understanding among the general public, and his positions in favor of scientific skepticism and against pseudoscience, such as his debunking of the Betty and Barney Hill abduction. To mark the tenth anniversary of Sagan's death, David Morrison, a former student of Sagan, recalled "Sagan's immense contributions to planetary research, the public understanding of science, and the skeptical movement" in ''Skeptical Inquirer''.

Sagan hypothesized in January 1991 that enough smoke from the 1991 Kuwaiti oil fires "might get so high as to disrupt agriculture in much of South Asia ..." He later conceded in ''The Demon-Haunted World'' that this prediction did not turn out to be correct: "it ''was'' pitch black at noon and temperatures dropped 4°–6 °C over the Persian Gulf, but not much smoke reached stratospheric altitudes and Asia was spared." A 2007 study noted that modern computer models have been applied to the Kuwait oil fires, finding that individual smoke plumes are not able to loft smoke into the stratosphere, but that smoke from fires covering a large area, like some forest fires or the burning of cities that would be expected to follow a nuclear strike, would loft significant amounts of smoke into the stratosphere.

In his later years Sagan advocated the creation of an organized search for near Earth objects that might impact the Earth. When others suggested creating large nuclear bombs that could be used to alter the orbit of a NEO that was predicted to hit the Earth, Sagan proposed the Deflection Dilemma: If we create the ability to deflect an asteroid away from the Earth, then we also create the ability to deflect an asteroid towards the Earth—providing an evil power with a true doomsday bomb.

Billions and billions

From ''Cosmos'' and his frequent appearances on ''The Tonight Show Starring Johnny Carson'', Sagan became associated with the catchphrase "billions and billions". Sagan stated that he never actually used the phrase in the ''Cosmos'' series. The closest that he ever came was in the book ''Cosmos'', where he talked of "billions ''upon'' billions": }}

However, his frequent use of the word ''billions'', and distinctive delivery emphasizing the "b" (which he did intentionally, in place of more cumbersome alternatives such as "billions with a 'b'", in order to distinguish the word from "millions" in viewers' minds), made him a favorite target of comic performers, including Johnny Carson, Gary Kroeger, Mike Myers, Bronson Pinchot, Penn Jillette, Harry Shearer, and others. Frank Zappa satirized the line in the song "Be In My Video", noting as well "atomic light". Sagan took this all in good humor, and his final book was entitled ''Billions and Billions'', which opened with a tongue-in-cheek discussion of this catchphrase, observing that Carson was an amateur astronomer and that Carson's comic caricature often included real science.

Similarly he is also known for expressing wonderment at the vastness of space and time, as in his phrase "The total number of stars in the Universe is larger than all the grains of sand on all the beaches of the planet Earth."

Sagan units

As a humorous tribute to him, a ''sagan'' has been defined as a unit of measurement equal to at least four billion, since the smallest number that may be described as ''billions and billions'' must be two billion plus two billion.

Social concerns

Sagan believed that the Drake equation, on substitution of reasonable estimates, suggested that a large number of extraterrestrial civilizations would form, but that the lack of evidence of such civilizations highlighted by the Fermi paradox suggests technological civilizations tend to self-destruct. This stimulated his interest in identifying and publicizing ways that humanity could destroy itself, with the hope of avoiding such a cataclysm and eventually becoming a spacefaring species. Sagan's deep concern regarding the potential destruction of human civilization in a nuclear holocaust was conveyed in a memorable cinematic sequence in the final episode of ''Cosmos'', called "Who Speaks for Earth?" Sagan had already resigned from the Air Force Scientific Advisory Board and voluntarily surrendered his top secret clearance in protest over the Vietnam War. Following his marriage to his third wife (novelist Ann Druyan) in June 1981, Sagan became more politically active—particularly in opposing escalation of the nuclear arms race under President Ronald Reagan.

In March 1983, Reagan announced the Strategic Defense Initiative—a multi-billion dollar project to develop a comprehensive defense against attack by nuclear missiles, which was quickly dubbed the "Star Wars" program. Sagan spoke out against the project, arguing that it was technically impossible to develop a system with the level of perfection required, and far more expensive to build than for an enemy to defeat through decoys and other means—and that its construction would seriously destabilize the nuclear balance between the United States and the Soviet Union, making further progress toward nuclear disarmament impossible.

When Soviet leader Mikhail Gorbachev declared a unilateral moratorium on the testing of nuclear weapons, which would begin on August 6, 1985—the 40th anniversary of the atomic bombing of Hiroshima—the Reagan administration dismissed the dramatic move as nothing more than propaganda, and refused to follow suit. In response, US anti-nuclear and peace activists staged a series of protest actions at the Nevada Test Site, beginning on Easter Sunday in 1986 and continuing through 1987. Hundreds of people were arrested, including Sagan, who was arrested on two separate occasions as he climbed over a chain-link fence at the test site.

Personal life and beliefs

Sagan was married three times—in 1957, to biologist Lynn Margulis, mother of Dorion Sagan and Jeremy Sagan; in 1968, to artist Linda Salzman, mother of Nick Sagan; and in 1981, to author Ann Druyan, mother of Alexandra Rachel (Sasha) Sagan and Samuel Democritus Sagan. His marriage to Druyan continued until his death in 1996.

Isaac Asimov described Sagan as one of only two people he ever met whose intellect surpassed his own. The other, he claimed, was the computer scientist and artificial intelligence expert Marvin Minsky.

Sagan wrote frequently about religion and the relationship between religion and science, expressing his skepticism about the conventional conceptualization of God as a sapient being. For example:

"Some people think God is an outsized, light-skinned male with a long white beard, sitting on a throne somewhere up there in the sky, busily tallying the fall of every sparrow. Others—for example Baruch Spinoza and Albert Einstein—considered God to be essentially the sum total of the physical laws which describe the universe. I do not know of any compelling evidence for anthropomorphic patriarchs controlling human destiny from some hidden celestial vantage point, but it would be madness to deny the existence of physical laws."

In another description of his view of God, Sagan emphatically writes:

"The idea that God is an oversized white male with a flowing beard who sits in the sky and tallies the fall of every sparrow is ludicrous. But if by God one means the set of physical laws that govern the universe, then clearly there is such a God. This God is emotionally unsatisfying... it does not make much sense to pray to the law of gravity."

On atheism, Sagan commented in 1981:

"An atheist is someone who is certain that God does not exist, someone who has compelling evidence against the existence of God. I know of no such compelling evidence. Because God can be relegated to remote times and places and to ultimate causes, we would have to know a great deal more about the universe than we do now to be sure that no such God exists. To be certain of the existence of God and to be certain of the nonexistence of God seem to me to be the confident extremes in a subject so riddled with doubt and uncertainty as to inspire very little confidence indeed".

In reply to a question in 1996 about his religious beliefs, Sagan answered, "I'm agnostic." Sagan's views on religion have been interpreted as a form of pantheism comparable to Einstein's belief in Spinoza's God. Sagan maintained that the idea of a creator of the universe was difficult to prove or disprove and that the only conceivable scientific discovery that could challenge it would be an infinitely old universe. According to his last wife, Ann Druyan, he was not a believer: }}

In 2006, Ann Druyan edited Sagan's 1985 Glasgow ''Gifford Lectures in Natural Theology'' into a book, ''The Varieties of Scientific Experience: A Personal View of the Search for God'', in which he elaborates on his views of divinity in the natural world. Sagan is also widely regarded as a freethinker or skeptic; one of his most famous quotations, in ''Cosmos'', was, "Extraordinary claims require extraordinary evidence" (called the "Sagan Standard" by some). This was based on a nearly identical statement by fellow founder of the Committee for the Scientific Investigation of Claims of the Paranormal, Marcello Truzzi, "An extraordinary claim requires extraordinary proof." This idea originated with Pierre-Simon Laplace (1749–1827), a French mathematician and astronomer who said, "The weight of evidence for an extraordinary claim must be proportioned to its strangeness."

Late in his life, Sagan's books elaborated on his skeptical, naturalistic view of the world. In ''The Demon-Haunted World: Science as a Candle in the Dark'', he presented tools for testing arguments and detecting fallacious or fraudulent ones, essentially advocating wide use of critical thinking and the scientific method. The compilation ''Billions and Billions: Thoughts on Life and Death at the Brink of the Millennium'', published in 1997 after Sagan's death, contains essays written by Sagan, such as his views on abortion, and his widow Ann Druyan's account of his death as a skeptic, agnostic, and freethinker.

Sagan warned against humans' tendency towards anthropocentrism. He was the faculty adviser for the Cornell Students for the Ethical Treatment of Animals. In the ''Cosmos'' chapter "Blues For a Red Planet", Sagan wrote, "If there is life on Mars, I believe we should do nothing with Mars. Mars then belongs to the Martians, even if the Martians are only microbes."

Sagan was a user and advocate of marijuana. Under the pseudonym "Mr. X", he contributed an essay about smoking cannabis to the 1971 book ''Marihuana Reconsidered''. The essay explained that marijuana use had helped to inspire some of Sagan's works and enhance sensual and intellectual experiences. After Sagan's death, his friend Lester Grinspoon disclosed this information to Sagan's biographer, Keay Davidson. The publishing of the biography, ''Carl Sagan: A Life'', in 1999 brought media attention to this aspect of Sagan's life. Not long after his death, widow Ann Druyan had gone on to preside over the board of directors of NORML, a foundation dedicated to reforming cannabis laws.

In 1994, engineers at Apple Computer code-named the Power Macintosh 7100 "Carl Sagan" in the hope that Apple would make "billions and billions" with the sale of the PowerMac 7100. The name was only used internally, but Sagan was concerned that it would become a product endorsement and sent Apple a cease and desist letter. Apple complied, but engineers retaliated by changing the internal codename to "BHA" for "Butt-Head Astronomer". Sagan then sued Apple for libel, a form of defamation, in federal court. The court granted Apple's motion to dismiss Sagan's claims and opined in dicta that a reader aware of the context would understand Apple was "clearly attempting to retaliate in a humorous and satirical way", and that "It strains reason to conclude that Defendant was attempting to criticize Plaintiff's reputation or competency as an astronomer. One does not seriously attack the expertise of a scientist using the undefined phrase 'butt-head'." Sagan then sued for Apple's original use of his name and likeness, but again lost. Sagan appealed the ruling. In November 1995, an out of court settlement was reached and Apple's office of trademarks and patents released a conciliatory statement that "Apple has always had great respect for Dr. Sagan. It was never Apple's intention to cause Dr. Sagan or his family any embarrassment or concern."

Sagan briefly served as an adviser on Stanley Kubrick's film ''2001: A Space Odyssey''. Sagan proposed that the film would suggest, rather than depict, extraterrestrial superintelligence.

Sagan and UFOs

Sagan had some interest in UFO reports from at least August 3, 1952 when he wrote a letter to U.S. Secretary of State Dean Acheson to ask how the U.S. would respond if flying saucers turned out to be extraterrestrial. He later had several conversations on the subject in 1964 with Jacques Vallee. Though quite skeptical of any extraordinary answer to the UFO question, Sagan thought scientists should study the phenomenon, at least because there was widespread public interest in UFO reports.

Stuart Appelle notes that Sagan "wrote frequently on what he perceived as the logical and empirical fallacies regarding UFOs and the abduction experience. Sagan rejected an extraterrestrial explanation for the phenomenon but felt there were both empirical and pedagogical benefits for examining UFO reports and that the subject was, therefore, a legitimate topic of study."

In 1966, Sagan was a member of the Ad Hoc Committee to Review Project Blue Book, the U.S. Air Force's UFO investigation project. The committee concluded Blue Book had been lacking as a scientific study, and recommended a university-based project to give the UFO phenomenon closer scientific scrutiny. The result was the Condon Committee (1966–1968), led by physicist Edward Condon, and in their final report they formally concluded that UFOs, regardless of what any of them actually were, did not behave in a manner consistent with a threat to national security.

Ron Westrum writes that "The high point of Sagan's treatment of the UFO question was the AAAS's symposium in 1969. A wide range of educated opinions on the subject were offered by participants, including not only proponents such as James McDonald and J. Allen Hynek but also skeptics like astronomers William Hartmann and Donald Menzel. The roster of speakers was balanced, and it is to Sagan's credit that this event was presented in spite of pressure from Edward Condon". With physicist Thornton Page, Sagan edited the lectures and discussions given at the symposium; these were published in 1972 as ''UFOs: A Scientific Debate''. Some of Sagan's many books examine UFOs (as did one episode of ''Cosmos'') and he claimed a religious undercurrent to the phenomenon.

Sagan again revealed his views on interstellar travel in his 1980 ''Cosmos'' series. In one of his last written works, Sagan argued that the chances of extraterrestrial spacecraft visiting Earth are vanishingly small. However, Sagan did think it plausible that Cold War concerns contributed to governments misleading their citizens about UFOs, and that "some UFO reports and analyses, and perhaps voluminous files, have been made inaccessible to the public which pays the bills ... It's time for the files to be declassified and made generally available." He cautioned against jumping to conclusions about suppressed UFO data and stressed that there was no strong evidence that aliens were visiting the Earth either in the past or present.

Death

After a long and difficult fight with myelodysplasia, which included three bone marrow transplants, Sagan died of pneumonia at the age of 62 at the Fred Hutchinson Cancer Research Center in Seattle, Washington, on December 20, 1996. He was buried at Lakeview Cemetery in Ithaca, New York.

Posthumous recognition

The 1997 movie ''Contact'', based on Sagan's novel of the same name and finished after his death, ends with the dedication "For Carl".

In 1997, the Sagan Planet Walk was opened in Ithaca, New York. It is a walking scale model of the solar system, extending 1.2 km from the center of The Commons in downtown Ithaca to the Sciencenter, a hands-on museum. The exhibition was created in memory of Carl Sagan, who was an Ithaca resident and Cornell Professor. Professor Sagan had been a founding member of the museum's advisory board.

The landing site of the unmanned Mars Pathfinder spacecraft was renamed the ''Carl Sagan Memorial Station'' on July 5, 1997. Asteroid 2709 Sagan is named in his honor.

Sagan's son, Nick Sagan, wrote several episodes in the ''Star Trek'' franchise. In an episode of ''Star Trek: Enterprise'' entitled "Terra Prime", a quick shot is shown of the relic rover Sojourner, part of the Mars Pathfinder mission, placed by a historical marker at Carl Sagan Memorial Station on the Martian surface. The marker displays a quote from Sagan: "Whatever the reason you're on Mars, I'm glad you're there, and I wish I was with you." Sagan's student Steve Squyres led the team that landed the Spirit Rover and Opportunity Rover successfully on Mars in 2004.

On November 9, 2001, on what would have been Sagan's 67th birthday, the NASA Ames Research Center dedicated the site for the Carl Sagan Center for the Study of Life in the Cosmos. "Carl was an incredible visionary, and now his legacy can be preserved and advanced by a 21st century research and education laboratory committed to enhancing our understanding of life in the universe and furthering the cause of space exploration for all time", said NASA Administrator Daniel Goldin. Ann Druyan was at the Center as it opened its doors on October 22, 2006.

Sagan has at least three awards named in his honor:

The Carl Sagan Memorial Award presented jointly since 1997 by the American Astronomical Society (AAS) and the Planetary Society,

The Carl Sagan Medal for Excellence in Public Communication in Planetary Science presented since 1998 by the American Astronomical Society's Division for Planetary Sciences (AAS/DPS) for outstanding communication by an active planetary scientist to the general public—Carl Sagan was one of the original organizing committee members of the DPS, and

The Carl Sagan Award for Public Understanding of Science presented by the Council of Scientific Society Presidents (CSSP)—Sagan was the first recipient of the CSSP award in 1993. In 2006, the Carl Sagan Medal was awarded to astrobiologist and author David Grinspoon, the son of Sagan's friend Lester Grinspoon.

On December 20, 2006, the tenth anniversary of Sagan's death, a blogger, Joel Schlosberg, organized a Carl Sagan "blog-a-thon" to commemorate Sagan's death, and the idea was supported by Nick Sagan. Many members of the blogging community participated.

August 2007 the Independent Investigative Group IIG awarded Sagan posthumously a Lifetime Achievement Award. This honor has also been awarded to Harry Houdini and James Randi.

Beginning in 2009, a musical project known as Symphony of Science sampled several excerpts of Sagan from his series Cosmos and remixed them to electronic music. To date, the videos have received over twenty-million views worldwide on the popular user generated website Youtube, and have exposed a new generation to the interconnected grandeur of the universe as Sagan described them in his documentary series.

Awards and honors

Annual Award for Television Excellence—1981—Ohio State University—PBS series ''Cosmos''

Apollo Achievement Award—National Aeronautics and Space Administration

NASA Distinguished Public Service Medal—National Aeronautics and Space Administration (twice)

Emmy—Outstanding Individual Achievement—1981—PBS series ''Cosmos''

Emmy—Outstanding Informational Series—1981—PBS series ''Cosmos''

Exceptional Scientific Achievement Medal—National Aeronautics and Space Administration

Helen Caldicott Leadership Award – Awarded by Women's Action for Nuclear Disarmament

Hugo Award—1981—''Cosmos''

Humanist of the Year—1981—Awarded by the American Humanist Association

In Praise of Reason Award—1987—Committee for the Scientific Investigation of Claims of the Paranormal

Isaac Asimov Award—1994—Committee for the Scientific Investigation of Claims of the Paranormal

John F. Kennedy Astronautics Award—American Astronautical Society

John W. Campbell Memorial Award—1974—''The Cosmic Connection: An Extraterrestrial Perspective''

Joseph Priestley Award—"For distinguished contributions to the welfare of mankind"

Klumpke-Roberts Award of the Astronomical Society of the Pacific—1974

Konstantin Tsiolkovsky Medal—Awarded by the Soviet Cosmonauts Federation

Locus Award 1986—''Contact''

Lowell Thomas Award—Explorers Club—75th Anniversary

Masursky Award—American Astronomical Society

Miller Research Fellowship—Miller Institute (1960–1962)

Oersted Medal—1990—American Association of Physics Teachers

Peabody Award—1980—PBS series ''Cosmos''

Prix Galbert—The international prize of Astronautics

Public Welfare Medal—1994—National Academy of Sciences

Pulitzer Prize for General Non-Fiction—1978—''The Dragons of Eden''

SF Chronicle Award—1998—''Contact''

Named the "99th Greatest American" on the June 5, 2005, ''Greatest American'' show on the Discovery Channel

Named an honorary member of the Demosthenian Literary Society on November 10, 2011

2009 New Jersey Hall of Fame inductee.

Publications

''Planets'' (LIFE Science Library), Sagan, Carl, Jonathan Norton Leonard and editors of Life, Time, Inc., 1966

''Intelligent Life in the Universe'', I.S. Shklovskii coauthor, Random House, 1966, ISBN 1-892803-02-X, 509 pgs (note: republished in 1998 by Emerson-Adams Press)

''UFOs: A Scientific Debate'', Thornton Page coauthor, Cornell University Press, 1972, 310 pgs

''Communication with Extraterrestrial Intelligence''. MIT Press, 1973, 428 pgs

''Mars and the Mind of Man'', Sagan, Carl, et al., Harper & Row, 1973, 143 pgs

''The Cosmic Connection: An Extraterrestrial Perspective'', Jerome Agel coauthor, Anchor Press, 1973, ISBN 0-521-78303-8, 301 pgs

''Other Worlds''. Bantam Books, 1975

''Murmurs of Earth: The Voyager Interstellar Record'', Sagan, Carl, et al., Random House, ISBN 0-394-41047-5, 1978

''The Dragons of Eden: Speculations on the Evolution of Human Intelligence''. Ballantine Books, 1978, ISBN 0-345-34629-7, 288 pgs

''Broca's Brain: Reflections on the Romance of Science''. Ballantine Books, 1979, ISBN 0-345-33689-5, 416 pgs

''Cosmos''. Random House, 1980. Random House New Edition, May 7, 2002, ISBN 0-375-50832-5, 384 pgs

''The Cold and the Dark: The World after Nuclear War'', Sagan, Carl et al., Sidgwick & Jackson, 1985

''Comet'', Ann Druyan coauthor, Ballantine Books, 1985, ISBN 0-345-41222-2, 496 pgs

''Contact''. Simon and Schuster, 1985; Reissued August 1997 by Doubleday Books, ISBN 1-56865-424-3, 352 pgs

''A Path Where No Man Thought: Nuclear Winter and the End of the Arms Race'', Richard Turco coauthor, Random House, 1990, ISBN 0-394-58307-8, 499 pgs

''Shadows of Forgotten Ancestors: A Search for Who We Are'', Ann Druyan coauthor, Ballantine Books, October 1993, ISBN 0-345-38472-5, 528 pgs

''Pale Blue Dot: A Vision of the Human Future in Space''. Random House, November 1994, ISBN 0-679-43841-6, 429 pgs

''The Demon-Haunted World: Science as a Candle in the Dark''. Ballantine Books, March 1996, ISBN 0-345-40946-9, 480 pgs (note: the book was first published and copyrighted in 1995 with an errata slip inserted)

''Billions and Billions: Thoughts on Life and Death at the Brink of the Millennium'', Ann Druyan coauthor, Ballantine Books, June 1997, ISBN 0-345-37918-7, 320 pgs

''The Varieties of Scientific Experience: A Personal View of the Search for God'', Carl Sagan (writer) & Ann Druyan (editor), 1985 Gifford lectures, Penguin Press HC, November 2006, ISBN 1-59420-107-2, 304 pgs

References

Further reading

External links

The Carl Sagan Portal

Video of skit from ''The Tonight Show Starring Johnny Carson'' mentioning "billions and billions"

BBC Radio program "Great Lives" on Carl Sagan's life

A Man whose time Has come—Interview with Carl Sagan by Ian Ridpath, New Scientist 1974 July 4

Carl Sagan Prize for Science Popularization

Sagan Medal for Excellence in Public Communication in Planetary Science, presented by the American Astronomical Society's Division for Planetary Sciences (AAS/DPS)

Carl Sagan Center for the Study of Life in the Universe, SETI Institute

Carl Sagan's Life and Legacy as Scientist, Teacher, and Skeptic, Committee for Skeptical Inquiry

A Tribute to Carl Sagan: Our Place in the Universe, The Skeptics Society

Category:1934 births Category:1996 deaths Category:Fellows at the University of California, Berkeley Category:American agnostics Category:American anti–nuclear weapons activists Category:American anti–Vietnam War activists Category:American astronomers Category:American cannabis activists Category:American humanists Category:American naturalists Category:American nature writers Category:American pacifists Category:American people of Russian-Jewish descent Category:American science fiction writers Category:American science writers Category:American skeptics Category:American UFO writers Category:Astrochemistry Category:Astrophysics Category:Cosmologists Category:Cornell University faculty Category:Deaths from pneumonia Category:Harvard University people Category:Infectious disease deaths in Washington (state) Category:Jewish American scientists Category:Jewish skeptics Category:Jewish agnostics Category:People from Brooklyn Category:Planetary scientists Category:Presenters of the Royal Institution Christmas Lectures Category:Pulitzer Prize for General Non-Fiction winners Category:Rahway High School alumni Category:Search for extraterrestrial intelligence Category:Interstellar messages Category:Space advocates Category:University of Chicago alumni Category:Gifford Lecturers Category:National Academy of Sciences laureates Category:The Planetary Society Category:Fellows of the Committee for Skeptical Inquiry

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name	Tom Lehrer
background	solo_singer
birth name	Thomas Andrew Lehrer
born	April 09, 1928New York, New York
instrument	VocalsPiano
occupation	Mathematician, teacher, lyricist, pianist, composer, singer/songwriter
years active	1945–1971, 1998
label	Reprise/Warner Bros. RecordsRhino/Atlantic RecordsShout! Factory
associated acts	Joe Raposo }}

Thomas Andrew "Tom" Lehrer (born April 9, 1928) is an American singer-songwriter, satirist, pianist, mathematician and polymath. He has lectured on mathematics and musical theater. Lehrer is best known for the pithy, humorous songs that he recorded in the 1950s and 1960s.

His work often parodies popular song forms, such as in "The Elements", where he sets the names of the chemical elements to the tune of the "Major-General's Song" from Gilbert and Sullivan's ''Pirates of Penzance''. Lehrer's earlier work typically dealt with non-topical subject matter and was noted for its black humor, seen in songs such as "Poisoning Pigeons in the Park". In the 1960s, he produced a number of songs dealing with social and political issues of the day, particularly when he wrote for the U.S. version of the television show ''That Was The Week That Was''.

In the early 1970s, he retired from public performances to devote his time to teaching mathematics and music theatre at the University of California, Santa Cruz. He did two additional performances in 1998 at a London gala show celebrating the career of impresario Cameron Mackintosh.

Early life

Lehrer was born in 1928 to a Jewish family in the New York City borough of Manhattan, and began studying classical piano music at the age of seven. He was more interested in the popular music of the age, however. Eventually, his mother also sent him to a popular-music piano teacher. At this early age, he began writing his own show tunes, which eventually helped him in his future adventures as a satirical composer and writer in his years of lecturing at Harvard University, and later at other universities.

Lehrer graduated from the Loomis Chaffee School in Windsor, Connecticut. He attended Camp Androscoggin, both as a camper and a counselor. While studying mathematics as an undergraduate student at Harvard College, he began to write comic songs to entertain his friends, including "Fight Fiercely, Harvard" (1945). Those songs were later named ''The Physical Revue'', a joking reference to a leading scientific journal, ''The Physical Review''.

Mathematics career

Lehrer earned his AB in mathematics (''magna cum laude'') from Harvard University in 1947, when he was nineteen. He received his MA degree the next year and was inducted into Phi Beta Kappa. He taught classes at MIT, Harvard, and Wellesley.

He remained in Harvard's doctoral program for several years, taking time out for his musical career and to work as a researcher at Los Alamos, New Mexico. He served in the Army from 1955 to 1957, working at the National Security Agency. (Lehrer has stated that he invented the Jell-O Shot during this time, as a means of circumventing liquor restrictions.) All of these experiences eventually became fodder for songs, viz. "Fight Fiercely, Harvard", "The Wild West Is Where I Want To Be" and "It Makes a Fellow Proud to Be a Soldier". Despite holding a master's degree in an era when American conscripts often lacked a high school diploma, Lehrer served as an enlisted soldier, achieving the rank of Specialist Four, which he described as being a "corporal without portfolio". In 1960, Lehrer returned to full-time studies at Harvard, but he never completed his doctoral studies in mathematics.

From 1962, he taught in the political science department at Massachusetts Institute of Technology (MIT). In 1972, he joined the faculty of the University of California, Santa Cruz, teaching an introductory course entitled "The Nature of Mathematics" to liberal arts majors—"Math for Tenors", according to Lehrer. He also taught a class in musical theater. He occasionally performed songs in his lectures, primarily those relating to the topic.

In 2001, Lehrer taught his last mathematics class (on the topic of infinity, and which was said to go on forever) and retired from academia. He has remained in the area, and still "hangs out" around the University of California, Santa Cruz.

His Erdős number is 4.

Mathematical publications

The American Mathematical Society database lists Lehrer as co-author of two papers:

RE Fagen & TA Lehrer, "Random walks with restraining barrier as applied to the biased binary counter", ''Journal of the Society for Industrial Applied Mathematics'', vol. 6, pp. 1–14 (March 1958) T Austin, R Fagen, T Lehrer, W Penney, "The distribution of the number of locally maximal elements in a random sample", ''Annals of Mathematical Statistics'' vol. 28, pp. 786–790 (1957)

Musical career

Lehrer was mainly influenced by musical theater. According to Gerald Nachtman's book Seriously Funny, the broadway musical, "Let's Face It" (lyrics by Sylvia Fine; music by Cole Porter) made an early and lasting impression. Lehrer's style consists of parodying various forms of popular song. For example, his appreciation of list songs led him to set an unordered list of the chemical elements to the tune of Gilbert and Sullivan's "Major-General's Song".

Author Isaac Asimov recounted in his second autobiographical volume ''In Joy Still Felt'' of seeing Lehrer perform in a Boston nightclub on October 9, 1954, during which Lehrer sang very cleverly about Jim getting it from Louise, and Sally from Jim, "and after a while you gathered the 'it' to be venereal disease [the song was likely "I Got It From Sally (in later versions 'Agnes')"]. Suddenly, as the combinations grew more grotesque, you realized he was satirizing every perversion known to mankind without using a single naughty phrase. It was clearly unsingable (in those days) outside a nightclub." Asimov also recalled a song that dealt with the Boston subway system, making use of the stations leading into town from Harvard, observing that the local subject-matter rendered the song useless for general distribution. Lehrer subsequently granted Asimov permission to print the lyrics to the subway song in his book. "I haven't gone to nightclubs often," said Asimov, "but of all the times I have gone, it was on this occasion that I had by far the best time."

Lehrer was inspired by the success of his performances of his own songs, so he paid for some studio time to record ''Songs by Tom Lehrer''. At the time, radio stations would not give Lehrer air time because of his controversial subjects. Instead, he sold his album on campus at Harvard for three dollars, while "supportive record merchants and dorm newsstands bought copies…and marked them up fifty cents." After one summer, he also started to receive mail orders from all parts of the country (as far away as San Francisco, after ''The Chronicle'' wrote an article on the record). Interest in his recordings was spread by word of mouth; friends and supporters brought their records home and played them for their friends, who then also wanted a copy.

The album—which included the macabre "I Hold Your Hand in Mine", the mildly risqué "Be Prepared", and "Lobachevsky" (regarding plagiarizing mathematicians) became a cult success via word of mouth, despite being self-published and without promotion. Lehrer then embarked on a series of concert tours and recorded a second album, which was released in two versions: the songs were the same, but ''More of Tom Lehrer'' was studio-recorded, while ''An Evening Wasted with Tom Lehrer'' was recorded live in concert.

Lehrer's major breakthrough in the United Kingdom came as a result of the citation accompanying an honorary degree given to Princess Margaret, where she cited musical tastes as "catholic, ranging from Mozart to Tom Lehrer". This prompted significant interest in his works and helped secure distributors for his material in the UK. It was there that his music achieved real popularity, as a result of the proliferation of university newspapers referring to the material, and the willingness of the BBC to play his songs on the radio (something that was a rarity in the United States).

By the early 1960s, Lehrer had retired from touring and was employed as the resident songwriter for the U.S. edition of ''That Was The Week That Was'' (TW3), a satirical television show. An increased proportion of his output became overtly political, or at least topical, on subjects such as education ("New Math"), the Second Vatican Council ("The Vatican Rag"), race relations ("National Brotherhood Week"), air and water pollution ("Pollution"), American militarism ("Send the Marines"), World War III "pre-nostalgia" ("So Long, Mom", premiered by Steve Allen), and nuclear proliferation ("Who's Next?" and "MLF Lullaby"). He also wrote a song that famously satirized the alleged amorality of rocket scientist Wernher von Braun, who had previously worked for Nazi Germany before working for the United States. ("'Once the rockets are up, who cares where they come down? That's not my department', says Wernher von Braun.") Lehrer did not appear on the television show; his songs were performed by a female vocalist and his lyrics were often altered by the network censors. Lehrer later performed the songs on the album, ''That Was The Year That Was'', so that, in his words, people could hear the songs the way they were intended to be heard.

In 1967, Lehrer was persuaded to make a short tour in Norway and Denmark, where he performed some of the songs from the television program. The performance in Oslo, Norway, on September 10 was recorded on video tape and aired locally later that autumn; this program was released on DVD some 40 years later.

Also around 1967, Lehrer composed and performed on piano original songs in a Dodge automobile "industrial" film that was distributed primarily to Dodge automobile dealers. It was also shown at promotional events organized by Dodge. Set in a fictional American wild west town, the full proper title of the film appears to be "The Dodge Rebellion Theatre presents Ballads For '67" Since the film is introducing 1967 model automobiles, it was possibly produced in late 1966.

The record deal with Reprise Records for the ''That Was The Year That Was'' album also gave Reprise distribution rights for Lehrer's earlier recordings, as Lehrer wanted to wind up his own record imprint. The Reprise issue of ''Songs by Tom Lehrer'' was a stereo re-recording. This version was not issued on CD, but the songs were issued on the live ''Tom Lehrer Revisited'' CD instead. The [live] recording also included bonus tracks "L-Y" and "Silent E", which Lehrer wrote for the PBS children's educational series ''The Electric Company''. Lehrer later commented that worldwide sales of the recordings under Reprise surpassed 1.8 million units in 1996. That same year, the album ''That Was The Year That Was'' went gold. The album liner notes (and Lehrer himself in one routine) promote Tom Lehrer's songs using reverse psychology, by deliberately quoting his negative reviews.

Departure from the music scene

There is an urban legend that Lehrer gave up political satire when the Nobel Peace Prize was awarded to Henry Kissinger in 1973. He did comment that awarding the prize to Kissinger made political satire obsolete, but has denied that he stopped creating satire thereafter as a form of protest, asserting that he had stopped several years prior to the award. Another mistaken belief is that he was sued for libel by the estate of Wernher Von Braun, the subject of one of his songs, and forced to relinquish all of his royalty income to Von Braun. Lehrer firmly denied this in a 2003 interview.

When asked about his reasons for abandoning his musical career, in an interview in the book accompanying his CD box set (released in 2000), he cited a simple lack of interest, a distaste for touring, and boredom with performing the same songs repeatedly. He observed that when he was moved to write and perform songs, he did, and when he was not, he did not, and that after a while he simply lost interest. Although many of Lehrer's songs satirized the Cold War political establishment of the era, he stopped writing and performing just as the 1960s counterculture movement gained momentum.

Lehrer's musical career was brief; in an interview in the late 1990s, he pointed out that he had performed a mere 109 shows and written 37 songs over 20 years. Nevertheless, he developed a significant cult following both in the United States and abroad.

In the 1970s, Lehrer concentrated on teaching mathematics and musical theater, although he also wrote ten songs for the children's television show ''The Electric Company''—Lehrer's Harvard schoolmate Joe Raposo was the show's musical director for its first three seasons.

Revivals and discographic reissues

In the early 1980s, ''Tom Foolery'', a revival of his songs on the London stage, was a hit. Although not its instigator, Lehrer eventually gave the stage production his full support and updated several of his lyrics for the production (such as "Who's Next", in which Neiman-Marcus [or in the San Francisco production, J.C. Penney], not Alabama, gets the bomb). ''Tom Foolery'' contained 27 Lehrer songs and led to more than 200 productions, including an off-Broadway production at the Village Gate, which ran for 120 performances in 1981.

In conjunction with the ''Tom Foolery'' premiere in 1980 at Criterion Theatre in London, Lehrer made a rare TV appearance on BBCs ''Parkinson'' show, where he sang "I Got It From Agnes".

On June 7 and 8, 1998, Lehrer performed in public for the first time in 25 years at the Lyceum Theatre, London as part of the gala show ''Hey, Mr. Producer!'' celebrating the career of impresario Cameron Mackintosh, who had been the producer of ''Tom Foolery''. The June 8 show was his only performance before Queen Elizabeth II. Lehrer sang "Poisoning Pigeons in the Park" and an updated version of the nuclear proliferation song "Who's Next?". The DVD of the event includes the former song.

In 2000, a boxed set of CDs, ''The Remains of Tom Lehrer'', was released by Rhino Entertainment. It included live and studio versions of his first two albums, ''That Was The Year That Was'', the songs he wrote for ''The Electric Company'', and some previously unreleased material. It was accompanied by a small hardbound book containing an introduction by Dr. Demento and lyrics to all the songs.

In 2010, Shout! Factory launched a reissue campaign, making his long out-of-press albums available digitally. They also issued a CD/DVD combo called ''The Tom Lehrer Collection'', which includes his best-loved songs, plus a DVD featuring an Oslo concert.

Musical legacy

Lehrer has commented that he doubts his songs had any real effect on those not already critical of the establishment: "I don't think this kind of thing has an impact on the unconverted, frankly. It's not even preaching to the converted; it's titillating the converted... I'm fond of quoting Peter Cook, who talked about the satirical Berlin kabaretts of the 1930s, which did so much to stop the rise of Hitler and prevent the Second World War."

In 2003 he commented that his particular brand of political satire is more difficult in the modern world: "The real issues I don't think most people touch. The Clinton jokes are all about Monica Lewinsky and all that stuff and not about the important things, like the fact that he wouldn't ban land mines... I'm not tempted to write a song about George W. Bush. I couldn't figure out what sort of song I would write. That's the problem: I don't want to satirise George Bush and his puppeteers, I want to vaporize them."

In a phone call to Gene Weingarten of the ''Washington Post'' in February 2008, Lehrer instructed Weingarten to "Just tell the people that I am voting for Obama."

A play, ''Letters from Lehrer'', written by Canadian Richard Greenblatt, was performed by him at CanStage, from January 16 to February 25, 2006. It followed Lehrer's musical career, the meaning of several songs, the politics of the time, and Greenblatt's own experiences with Lehrer's music, while playing some of Lehrer's songs. There are currently no plans for more performances, although low-quality audio recordings have begun to circulate around the internet.

Some of his songs ("I Hold Your Hand in Mine" and "Poisoning Pigeons in the Park") were reworked into German by the Austrian-Jewish singer satirist Georg Kreisler who lived in the United States from 1938 until 1955. Lehrer was praised by Dr. Demento as "the best musical satirist of the twentieth century". Other artists who cite Lehrer as an influence include "Weird Al" Yankovic, whose work generally addresses more popular and less technical or political subjects, and educator and scientist H. Paul Shuch, who tours under the stage name Dr. SETI and calls himself "a cross between Carl Sagan and Tom Lehrer: he sings like Sagan and lectures like Lehrer." More stylistically influenced performers include American political satirist Mark Russell, and the British duo Kit and The Widow. British medical satirists Amateur Transplants acknowledge the debt they owe to Tom Lehrer on the back of their first album, ''Fitness to Practice''. Their songs "The Menstrual Rag" and "The Drugs Song" are to the tunes of Lehrer's "The Vatican Rag" and "The Elements" (itself set to the tune of the "Major-General's Song" from ''The Pirates of Penzance'' by Gilbert and Sullivan), respectively. Their second album, ''Unfit to Practise'', opens with an update of Lehrer's "The Masochism Tango" and is called simply "Masochism Tango 2008". Syndicated conservative morning-radio talk show host Jim Quinn sings with piano backing in a Lehrer-like tribute in a song on how political correctness has destroyed so many Christmas traditions with the song "A Politically Correct Christmas".

Lehrer has said of his musical career, "If, after hearing my songs, just one human being is inspired to say something nasty to a friend, or perhaps to strike a loved one, it will all have been worth the while."

Music lists

Reviews selected by Lehrer for his liner notes

"Mr. Lehrer's muse is not fettered by such inhibiting factors as taste." — ''The New York Times'' (9 February 1959)

"More desperate than amusing" — ''New York Herald Tribune''

"He seldom has any point to make except obvious ones" — ''The Christian Science Monitor''

"Plays the piano acceptably" — ''The Oakland Tribune''

Solo discography

''Songs by Tom Lehrer'' (1953)

''More of Tom Lehrer'' (1959)

''An Evening Wasted with Tom Lehrer'' (1959)

''Revisited'' (1960) (1990 CD reissue includes 1971 studio recordings of ''Silent E'' and ''L-Y'')

''Tom Lehrer Discovers Australia (And Vice Versa)'' (1960; Australia-only)

''That Was the Year That Was'' (1965)

''Tom Lehrer in Concert'' (1994; UK compilation)

''Songs & More Songs by Tom Lehrer'' (1997)

''The Remains of Tom Lehrer'' (2000)

''The Tom Lehrer Collection'' (2010)

Many Lehrer songs also are performed (but not by Lehrer) in ''That Was The Week That Was'' (Radiola LP, 1981)

The sheet music to many of Lehrer's songs is published in ''The Tom Lehrer Song Book'' (Crown Publishers, Inc., 1954) Library of Congress Card Catalog Number 54-12068 and ''Too Many Songs by Tom Lehrer: with not enough drawings by Ronald Searle'' (Pantheon, 1981, ISBN 0-394-74930-8).

References

External links

That Was the Wit That Was Tom Lehrer interview in SF Weekly, published 2000-04-19, retrieved 2010-08-26

Tom Lehrer Annotated Song Lyrics, many with MIDI files, collected by Graeme Cree, retrieved 2011-04-13

59 minute long mp3 radio programme from 1983, with a telephone interview with Tom Lehrer, as well as a 10 minute follow-up 1989 From "Bob Claster's Funny Stuff" on KCRW, retrieved 2010-08-26

A Conversation with Tom Lehrer done by Paul D. Lehrman on September 7, 1997, retrieved 2010-08-26

Tom Lehrer page on The Demented Music Database - includes biography, discography, lyrics and other miscellanea, retrieved on 2011-01-23

Category:1928 births Category:Living people Category:20th-century mathematicians Category:American male singers Category:American mathematicians Category:American novelty song performers Category:American satirists Category:American singer-songwriters Category:American pianists Category:American comedy musicians Category:Harvard University alumni Category:Reprise Records artists Category:Comedy musicians Category:Massachusetts Institute of Technology faculty Category:Parody musicians Category:University of California, Santa Cruz faculty Category:Horace Mann School alumni Category:United States Army soldiers Category:Jewish songwriters Category:Wellesley College faculty Category:Jewish comedians Category:American Jews Category:American Jews

ar:توم لهرر da:Tom Lehrer de:Tom Lehrer es:Tom Lehrer fr:Tom Lehrer he:טום לרר ht:Tom Lehrer nl:Tom Lehrer ja:トム・レーラー no:Tom Lehrer pt:Tom Lehrer ru:Лерер, Том sv:Tom Lehrer uk:Том Лерер

Birth name	Daniel Jacob Radcliffe
Birth date	July 23, 1989
Birth place	London, England
Occupation	Actor
Years active	1999–present
known for	}}

Daniel Jacob Radcliffe (born 23 July 1989) is an English actor who rose to prominence playing the titular character in the ''Harry Potter'' film series. His work on the series has earned him several awards and more than £60 million.

Radcliffe made his acting debut at age ten in BBC One's television movie ''David Copperfield'' (1999), followed by his film debut in 2001's ''The Tailor of Panama''. Cast as Harry at the age of eleven, Radcliffe has starred in eight ''Harry Potter'' films since 2001, with the final instalment released in July 2011. In 2007 Radcliffe began to branch out from the series, starring in the London and New York productions of the play ''Equus'', and the 2011 Broadway revival of the musical ''How to Succeed in Business Without Really Trying''. ''The Woman in Black'' (2012) will be his first film project following the final ''Harry Potter'' movie.

Radcliffe has contributed to many charities, including Demelza House Children's Hospice and The Trevor Project. He has also made public service announcements for the latter. In 2011 the actor was awarded the Trevor Project's "Hero Award".

Early life

Radcliffe was born on 23 July 1989 in West London, England, the only child of Alan George Radcliffe, a literary agent, and Marcia Jeannine Gresham (née Marcia Gresham Jacobson), a casting agent who was involved in several films for the BBC, including ''The Inspector Lynley Mysteries'' and ''Walk Away And I Stumble.'' Radcliffe's mother is Jewish and a native of Westcliff-on-Sea, Essex (her family's surname was anglicised from "Gershon"); his father, originally from Northern Ireland, is Protestant. Radcliffe first expressed a desire to act at the age of five. In December 1999, aged ten, he made his acting debut in the BBC One's televised two-part adaptation of the Charles Dickens novel ''David Copperfield'', portraying the title character as a young boy. Radcliffe was educated at independent schools for boys, including Sussex House School, a day school in Cadogan Square in Chelsea, London.

Following the release of the first ''Harry Potter'' movie, attending school became hard, with some students becoming hostile. Radcliffe said it was people just trying to "have a crack at the kid that plays Harry Potter" rather than jealousy. As his acting career began to consume his schedule, Radcliffe continued his education through on-set tutors. The actor admitted he was not very good at school, considered it useless, and found the work to be "really, really difficult." However, he did achieve A grades in the three Advanced levels he sat in 2006 but then decided to take a break from education and did not go to college or university. Part of the reason was he already knew he wanted to act and write. Another reason was it would be difficult to have a normal college experience. "The paparazzi, they’d love it,” he told ''Details'' magazine in 2007. "If there were any parties going on, they’d be tipped off as to where they were, and it would be all of that stuff."

Career

''Harry Potter''

In 2000, producer David Heyman asked Radcliffe to audition for the role of Harry Potter for the film adaptation of ''Harry Potter and the Philosopher's Stone'', the best-selling book by British author J.K. Rowling. The author had been searching for an unknown British actor to personify the character. However, Radcliffe's parents did not want him to audition for the role as the contract required shooting all seven films in Los Angeles, California, so they did not tell him. Once the movie's director Chris Columbus saw a video of the young actor in ''David Copperfield'', he recalled thinking, "This is what I want. This is Harry Potter". Eight months later, after several auditions, he was selected to play the part. Rowling also endorsed the selection, saying the filmmaker could not "have found a better Harry". Warner Bros offered him a two-movie contract, with shooting in the UK, and assured his parents he would be protected. When signing up, Radcliffe was unsure if he would do any more pictures.

The release of ''Harry Potter and the Philosopher's Stone'' (released as ''Harry Potter and the Sorcerer's Stone'' in the United States) took place in 2001. The story follows Harry, a young boy who learns he is a wizard and is sent to Hogwarts School of Witchcraft and Wizardry to begin his magical education. He got a seven figure salary for the lead role but asserted that the fee was not "that important" to him. His parents chose to invest the money for him. The film broke records for opening-day sales and opening-weekend takings and became the highest-grossing film of 2001. With a total of US$974 million in ticket sales, ''Philosopher's Stone'' stands as the second most commercially successful in the series, behind the final installment. The adaptation met with strong reviews, and critics took notice of Radcliffe: "Radcliffe is the embodiment of every reader's imagination. It is wonderful to see a young hero who is so scholarly looking and filled with curiosity and who connects with very real emotions, from solemn intelligence and the delight of discovery to deep family longing," wrote Bob Graham of the ''San Francisco Chronicle''.

A year later, Radcliffe starred in ''Harry Potter and the Chamber of Secrets'', the second instalment of the series. Reviewers were positive about the lead actors' performances but had polarised opinions on the movie as a whole. Stephen Hunter of the ''Washington Post'' labelled it "big, dull and empty", whereas Desson Thomson of the same publication had more positive feelings. Observing that Radcliffe and his peers had matured, ''Los Angeles Times'''s staff writer Kenneth Turan believed the novel's magic could not be successfully duplicated in the film. Nonetheless, it still managed to earn US$878 million, taking the second spot of the highest-grossing 2002 films worldwide behind ''The Lord of the Rings: The Two Towers''

The 2004 release ''Harry Potter and the Prisoner of Azkaban'' marked the third in the series. While garnering the highest critical acclaim of the series and grossing US$795.6 million worldwide, the film's performance at the box office ranks the lowest in the series. Meanwhile, Radcliffe's performance was panned by critics, who found him to be "wooden", with ''New York Times'' journalist A. O. Scott writing that Watson had to carry him with her performance. Next was ''Harry Potter and the Goblet of Fire'' in 2005. The film explored romantic elements, included more humour and saw Harry selected as a competitor in a dangerous multi-wizard school competition. ''Goblet of Fire'' set records for a ''Harry Potter'' opening weekend, as well as for a non-May opening weekend in the US and an opening weekend in the UK. In a 2005 interview, Radcliffe singled out the humour as being a reason for the movie's creative success.

Despite the success of the past movies, the future of the franchise was put into question as all three lead actors were unsure about signing on to continue their roles for the final two episodes. However, by 2 March 2007, Radcliffe signed for the final films, which put an end to weeks of press speculation that he would be denied the part due to his involvement in ''Equus''. Radcliffe reprised his role for the fifth time in ''Harry Potter and the Order of the Phoenix'' (2007), which details Harry's return to Hogwarts after his recent encounter with Lord Voldemort. It opened to positive responses from the press. IGN movie critic Steven Horn found ''Order of the Phoenix'' to be one of "those rare films that exceeds the source material" and Colin Bertram of New York's ''Daily News'' publication dubbed it the best movie in the series. Radcliffe has stated that he had formed a special bond with actor Gary Oldman while working with him on set and that director David Yates and actress Imelda Staunton made ''Order of the Phoenix'' the "most fun" film in the series to work on. His performance earned several nominations, and he picked up the 2008 National Movie Award for "Best Male Performance". As the fame of the actor and the series continued, Radcliffe and fellow ''Harry Potter'' cast members Rupert Grint and Emma Watson left imprints of their hands, feet, and wands in front of Grauman's Chinese Theater in Hollywood.

On 15 July 2009, the series's sixth instalment, ''Harry Potter and the Half-Blood Prince'', was released. It centres around Harry discovering an old book belonging to the Half-Blood Prince and beginning to learn more about Lord Voldemort's past. The film did considerably better than the previous movie, breaking the then-record for biggest midnight US showings, with US$22.2 million at 3,000 theatres and with US$7 million, giving the UK its biggest Wednesday ever. In its total run, ''Half-Blood Prince'' totalled in US$933 million ticket sales. The film remains one of the most positively reviewed entries within the series among film critics, who praised the film's "emotionally satisfying" story, direction, cinematography, visuals and music. At the 2010 MTV Movie Awards, Radcliffe received nominations for "Best Male Performance" and "Global Superstar".

For financial and scripting reasons, the last book was divided into two films that were shot back to back, drawing criticism from the book's fanbase. The actor defended the split, pointing out that it would have been impossible to properly adapt the final novel into a single film. He added that the last movie was going to be extremely fast-paced with a lot of action, while the first part would be far more sedate, focussing on character development. Had they combined them, those things would not have made it to the final cut. Filming lasted for a year, concluding in June 2010. On the last day of shooting, like most of the cast and crew, Radcliffe openly wept. ''Harry Potter and the Deathly Hallows - Part 1'' (2010) was released in November and grossed over US$950 million. Its most lucrative territory was the UK, where it reportedly had the highest-grossing three-day opening in history. Overseas, its earnings of US$205 million in 91 markets made it the top-grossing foreign opening for a non-summer picture. The movie received mostly favourable reviews in the media.

The final film, ''Harry Potter and the Deathly Hallows - Part 2'', was released worldwide starting on 13 July 2011 in Australia. It was named the most highly anticipated film of 2011 by Fandango users and won the National Movie Awards's "Must See Movie of the Summer" accolade. Radcliffe admitted that some people would never be able to separate him from the character but also said he is "proud to be associated with this film series forever." Despite positive feelings about the movies, he has no interest in doing more ''Harry Potter'' films. After Rowling suggested writing an eighth book, Radcliffe was asked if he would do another film; he replied: "[It is] very doubtful. I think 10 years is a long time to spend with one character." Despite devoting so much time to the series, Radcliffe has asserted that he did not miss out on a childhood like other child actors: "I’ve been given a much better perspective on life by doing ''Potter''.

Other acting work

Prior to ''Harry Potter'', Radcliffe made his film debut in ''The Tailor of Panama'', an American 2001 film based on John le Carré's 1996 spy novel and a moderate commercial success. In 2002, he made his stage debut as a celebrity guest in the West End production ''The Play What I Wrote'' directed by Kenneth Branagh, who appeared with him in the second ''Harry Potter'' movie. In 2007, he appeared in ''December Boys'', an Australian family drama about four orphans that was shot in 2005 and released to theatres in mid-September 2007. Also in 2007, Radcliffe co-starred with Carey Mulligan in ''My Boy Jack'', a television drama film shown on ITV on Remembrance Day. The TV film received mostly good reviews, with several critics praising Radcliffe's performance as an 18 year-old who goes missing in action during a battle. Radcliffe stated, "For many people my age, the First World War is just a topic in a history book. But I've always been fascinated by the subject and think it's as relevant today as it ever was."

At age 17, in a bid to show people he was not a kid anymore, he performed onstage in Peter Shaffer's play ''Equus'', which had not been revived since its first run in 1973. Radcliffe took on the lead role as Alan Strang, a stable boy who has an obsession with horses, at the Gielgud Theatre. The role generated significant pre-opening media interest and advance sales topped £1.7 million, as Radcliffe appeared in a nude scene. ''Equus'' opened on 27 February 2007 and ran until 9 June 2007. Radcliffe's performance received positive reviews as critics were impressed by the nuance and depth of his against-type role. Charles Spencer of ''The Daily Telegraph'' wrote that he "displays a dramatic power and an electrifying stage presence that marks a tremendous leap forward." He added: "I never thought I would find the diminutive (but perfectly formed) Radcliffe a sinister figure, but as Alan Strang, [...] there are moments when he seems genuinely scary in his rage and confusion." The production then transferred to Broadway in September 2008 with Radcliffe still in the lead role. Radcliffe stated he was nervous about repeating the role on Broadway because he considered American audiences more discerning than those in London. Radcliffe's performance was nominated for a Drama Desk Award.

After voicing a character in an episode of the animated television series ''The Simpsons'' in late 2010, Radcliffe debuted as J. Pierrepont Finch in the 2011 Broadway revival ''How to Succeed in Business Without Really Trying'', a role previously held by Broadway veterans Robert Morse and Matthew Broderick. Other cast members included Rose Hemingway and Mary Faber. Both the actor and production received favourable reviews, with the latter receiving 9 Tony Award nominations. His first post-''Harry Potter'' project will be the 2012 supernatural thriller ''The Woman in Black'', which is adapted from the 1983 novel by Susan Hill and set for a February release in the UK. Radcliffe portrays a man sent to deal with the legal matters of a mysterious woman who has just died. Soon after, he begins to experience strange events and hauntings from the ghost of a woman dressed in black. He said he was "incredibly excited" to be part of the film and described the script as "beautifully written". ''Variety'' confirmed Radcliffe will star in the indie comedy ''The Amateur Photographer'', a film adaptation of the book of the same name, directed by Christopher Monger. Set in 1970, it follows a man (Radcliffe) who discovers his calling after being drafted by the residents of a small England mill town to serve as a photographer for their most personal moments.

Personal life

In 2007, Radcliffe was in a relationship with Laura O'Toole, an understudy for one of his co-stars in a play. Following the break-up, they remained friends. He is an atheist and has also stated that he is "very proud of being Jewish." In 2008, he revealed that he suffers from a mild form of the neurological disorder dyspraxia. The motor skill disorder sometimes gets so bad that he has trouble doing simple activities, such as writing or tying his own shoelaces. "I was having a hard time at school, in terms of being crap at everything, with no discernible talent," the actor commented. In August 2010, he stopped drinking alcohol after finding himself becoming too reliant on it.

Radcliffe is a supporter of the Liberal Democrats. He has voiced support for the political party's Nick Clegg and pledged to spend more time in the UK to help increase his profile to a younger audience. At the age of 16, Radcliffe became the youngest non-royal ever to have an individual portrait in Britain's National Portrait Gallery. On 13 April 2006, his portrait, drawn by Stuart Pearson Wright, was unveiled as part of a new exhibition opening at the Royal National Theatre, then moved to NPG where it resides.

He is a fan of underground and punk rock music, and is a keen follower of cricket, including cricketer Sachin Tendulkar. Writing short stories and poetry is also a passion. In November 2007, the actor published several poems under the pen name Jacob Gershona combination of his middle name and the Jewish version of his mother's maiden name Gresham in ''Rubbish'', an underground fashion magazine. He enjoys a close friendship with his fellow ''Harry Potter'' co-stars Emma Watson and Tom Felton and is tight-knit with his family, whom he credits for keeping him grounded.

Speaking out against homophobia, Radcliffe filmed public service announcements for The Trevor Project promoting awareness of gay teen suicide prevention beginning in 2009. He first learned of the organisation while working on ''Equus'' on Broadway in 2008 and has contributed financially to it. "I have always hated anybody who is not tolerant of gay men or lesbians or bisexuals. Now I am in the very fortunate position where I can actually help or do something about it," he said in a 2010 interview. In the same interview, he spoke of the importance of public figures advocating for equal rights. Radcliffe considers his involvement to be one of the most important things in his career. For his work for the organisation, he was given the "Hero Award" in 2011.

Radcliffe has supported various charities. He designed a Cu-Bed for Habitat's VIP Kids range, and all the royalties from the sale of the bed went directly to his favourite charity, Demelza House Children's Hospice, in Sittingbourne, Kent. Radcliffe has urged his fans to make donations in lieu of Christmas presents to him to that charity's Candle for Care program. In 2008, he was among several celebrities to donate their old eyeglasses to an exhibit honouring victims of the Holocaust. During the Broadway run of ''Equus'', the actor also auctioned off a pair of jeans he wore in the show for several thousand dollars. He has also donated money to Get Connected UK, a London-based free confidential national helpline for troubled youth.

He is reported to have earned £1 million for the first ''Potter'' film and around £15 million for the sixth movie. Radcliffe appeared on the ''Sunday Times'' Rich List in 2006, which estimated his personal fortune to be £14 million, making him one of the richest young people in the UK. In March 2009, he was ranked number one on the ''Forbes'' list of "Most Valuable Young Stars". By April, ''The Daily Telegraph'' measured his net worth at £30m, making him the 12th richest young person in the UK. According to the publication, he is expected to have amassed £70m by the time the series of movies concludes. Radcliffe was considered to be the richest teenager in England as of June 2009. In February 2010, he was named the sixth highest paid Hollywood male star and placed at number five on ''Forbes''s December list of Hollywood's highest-grossing actors, with the revenue of US$780 million thanks to one movie released that year: ''Harry Potter and the Deathly Hallows''. The actor was reported in 2010 to have personal assets of £28.5 million, making him richer than Princes William and Harry. Despite his wealth, Radcliffe has said he does not have expensive tastes. His main expense is buying books: "I read a lot." He also stated that money would never be the focus of his life.

Screen and stage credits

Films

! Year	! Title	! Role	Notes
2001	''The Tailor of Panama''	Mark Pendel
2001			Released as ''Harry Potter and the Sorcerer's Stone'' in the US and India
2002		Harry Potter
2004		Harry Potter
2005		Harry Potter
2007		Harry Potter
2007	''December Boys''	Maps
2009		Harry Potter
2010	''Harry Potter and the Deathly Hallows – Part 1''	Harry Potter
2011	''Harry Potter and the Deathly Hallows – Part 2''	Harry Potter
2012		Arthur Kipps	Post-production

Television

! Year	! Title	! Role	Notes
1999		young David Copperfield	Television film shown on BBC One
2005	''Foley and McColl: This Way Up''	Traffic Warden/Himself
2006		Boy Scout/Himself
2007		Jack Kipling	Television film shown on ITV
2010	''The Simpsons''	Edmund	"Treehouse of Horror XXI", voice part
2010		Himself	BBC comedy panel game television program

Stage

! Year	! Title	! Role	Notes
2002	''The Play What I Wrote''	Guest	Wyndham's Theatre
2007		Alan Strang	Gielgud Theatre
2008	''Equus''	Alan Strang	Broadhurst Theatre
2011	''How to Succeed in Business Without Really Trying''	J. Pierrepont Finch	Al Hirschfeld Theatre

Awards

! Year !! Organisation !! Award !! Work !! Result
2001		Best Young Performer
2001	Hollywood Women's Press Club	Male Youth Discovery of the Year	''Harry Potter and the Philosopher's Stone''
2001	MTV Movie Awards		''Harry Potter and the Philosopher's Stone''
2001	Young Artist Awards	Best Ensemble in a Feature Film (shared with the movies cast)	''Harry Potter and the Philosopher's Stone''
2002	Bravo Silver Otto	Best Male Actor	''Harry Potter and the Philosopher's Stone''
2003	Saturn Awards	Best Performance by a Young Actor
2003	Bravo Silver Otto	Best Male Actor	''Harry Potter and the Chamber of Secrets''
2003	SyFy Portal Genre Awards	Best Young Actor	''Harry Potter and the Chamber of Secrets''
2003	Portal Awards	Best Young Actor	''Harry Potter and the Chamber of Secrets''
2004	Bravo Bronze Otto	Best Male Actor
2004	ITV Celebrity Awards	Young Talent of the Year	''Harry Potter and the Prisoner of Azkaban''
2005	Broadcast Film Critics Association Awards	Best Young Actor	''Harry Potter and the Prisoner of Azkaban''
2005	Portal Awards	Best Young Actor	''Harry Potter and the Prisoner of Azkaban''
2006	Bravo Golden Otto	Male Film Star
2006	MTV Movie Awards		''Harry Potter and the Goblet of Fire''
2006	MTV Movie Awards		''Harry Potter and the Goblet of Fire''
2006	Portal Awards	Best Actor/Movie	''Harry Potter and the Goblet of Fire''
2006	Broadcast Film Critics Association Awards	Best Young Actor	''Harry Potter and the Goblet of Fire''
2007	Scream Awards	Fantasy Hero
2007	National Movie Awards	Best Male Performance	''Harry Potter and the Order of the Phoenix''
2008	Empire Award	Best Actor	''Harry Potter and the Order of the Phoenix''
2008	Bravo Golden Otto	Best Male Actor	''Harry Potter and the Order of the Phoenix''
2008	MTV Movie Awards		''Harry Potter and the Order of the Phoenix''
2008	Saturn Awards	Best Performance by a Young Actor	''Harry Potter and the Order of the Phoenix''
2008	Theatregoers' Choice Awards	Dewynters London Newcomer of the Year
2009	Broadway.com Audience Award	Favorite Leading Actor in a Broadway Play
2009	Broadway.com Audience Award	Favorite Breakthrough Performance	''Equus''
2009	Drama Desk Awards		''Equus''
2009	Drama League Award	Distinguished Performance Award	''Equus''
2009	Scream Awards	Best Fantasy Actor	''Harry Potter and the Half-Blood Prince''
2010	National Movie Awards	Best Performance	''Harry Potter and the Half-Blood Prince''
2010	Portal Awards	Best Young Actor	''Harry Potter and the Half-Blood Prince''
2010		Iconic Movie Star
2010	People's Choice Awards	Best On-Screen Team (shared with Rupert Grint and Emma Watson)	''Harry Potter and the Half-Blood Prince''
2010	MTV Movie Award	Best Male Performance	''Harry Potter and the Half-Blood Prince''
2010	MTV Movie Award	Global Superstar
2011	National Movie Awards	Performance Of The Year	''Harry Potter and the Deathly Hallows Part 1''
2011	Broadway.com Audience Award	Favorite Actor in a Broadway Play	''How to Succeed in Business Without Really Trying''
2011	Broadway.com Audience Award	Favorite Onstage Pair (with John Larroquette)	''How to Succeed in Business Without Really Trying''
2011	Drama Desk Award		''How to Succeed in Business Without Really Trying''
2011	Outer Critic's Circle Award	Outstanding Actor In A Musical	''How to Succeed in Business Without Really Trying''
2011	BroadwayWorld.com	Best Leading Actor in a Musical	''How to Succeed in Business Without Really Trying
2011	MTV Movie Award	Best Kiss (shared with Emma Watson)	''Harry Potter and the Deathly Hallows Part 1''
2011	MTV Movie Award	Best Fight (shared with Rupert Grint and Emma Watson)	''Harry Potter and the Deathly Hallows Part 1''
2011	MTV Movie Award	Best Male Performance	''Harry Potter and the Deathly Hallows Part 1''
2011	Trevor Project	Trevor Hero Award
2011	Teen Choice Awards	Choice Movie Actor: Sci-Fi/Fantasy	''Harry Potter and the Deathly Hallows Part 1''
2011	Teen Choice Awards	Choice Movie: Liplock (shared with Emma Watson)	''Harry Potter and the Deathly Hallows Part 1''
2011	Teen Choice Awards	Choice Summer Movie Star: Male	''Harry Potter and the Deathly Hallows Part 2''
2011	Do Something Awards	Movie Star
2011	Portal Awards	Best Young Actor	''Harry Potter and the Deathly Hallows Part 1''

See also

List of Harry Potter films cast members

References

Further reading

External links

Category:1989 births Category:English atheists Category:English child actors Category:English film actors Category:English Jews Category:English people of Northern Ireland descent Category:English stage actors Category:English television actors Category:Jewish actors Category:Jewish atheists Category:Living people Category:Actors from London Category:Old Citizens (City of London School) Category:People from Hammersmith Category:LGBT rights activists from England

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