Land mass refers to the total surface area of a geographical region or country (which may include discontinuous pieces of land such as islands). The Earth's total land mass is 148,939,063.133 km² (57,505,693.767 sq mi) which is about 29.2% of its total surface. Water covers approximately 70.8% of the Earth's surface, mostly in the form of oceans.

Dry land redirects here. It may refer to:

Land may refer to:

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People:

As a synonym for a region belonging to a people:

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In physics, mass (from Greek μᾶζα "barley cake, lump (of dough)"), more specifically inertial mass, can be defined as a quantitative measure of an object's resistance to the change of its speed. In addition to this, gravitational mass can be described as a measure of magnitude of the gravitational force which is

when interacting with a second object. The SI unit of mass is the kilogram (kg).

In everyday usage, mass is often referred to as weight, the units of which are often taken to be kilograms (for instance, a person may state that their weight is 75 kg). In scientific use, however, the term weight refers to a different, yet related, property of matter. Weight is the gravitational force acting on a given body—which differs depending on the gravitational pull of the opposing body (e.g. a person's weight on Earth vs on the Moon) — while mass is an intrinsic property of that body that never changes. In other words, an object's weight depends on its environment, while its mass does not. On the surface of the Earth, an object with a mass of 50 kilograms weighs 491 Newtons; on the surface of the Moon, the same object still has a mass of 50 kilograms but weighs only 81.5 Newtons. Restated in mathematical terms, on the surface of the Earth, the weight W of an object is related to its mass m by W = mg, where g is the Earth's gravitational field strength, equal to about 9.81 m/s².

Neil deGrasse Tyson ( /ˈniːəl dəˈɡræs ˈtaɪsən/ born October 5, 1958) is an American astrophysicist and science communicator. He is currently the Frederick P. Rose Director of the Hayden Planetarium at the Rose Center for Earth and Space, and a research associate in the department of astrophysics at the American Museum of Natural History. Since 2006 he has hosted the educational science television show NOVA scienceNOW on PBS, and has been a frequent guest on The Daily Show, The Colbert Report, Real Time with Bill Maher, and Jeopardy!. It was announced on August 5, 2011, that Tyson will be hosting a new sequel to Carl Sagan's Cosmos: A Personal Voyage television series.

Tyson was born as the second of three children in the borough of Manhattan in New York City, but was raised in the Bronx. His mother, Sunchita Feliciano Tyson, was a gerontologist and his father, Cyril deGrasse Tyson, was a sociologist, human resource commissioner for the New York City mayor, John Lindsay, and was the first Director of HARYOU. Tyson attended the Bronx High School of Science (1972–1976, astrophysics emphasis) where he was captain of the wrestling team and was editor-in-chief of the school's Physical Science Journal. Tyson had an abiding interest in astronomy from the age of eleven, following his visit to the Hayden Planetarium at age nine. Tyson recalls that "so strong was that imprint [of the night sky] that I'm certain that I had no choice in the matter, that in fact, the universe called me." He obsessively studied astronomy in his teens, and eventually even gained some fame in the astronomy community by giving lectures on the subject at the age of fifteen.