Earth Day is an annual day on which events are held worldwide to increase awareness and appreciation of the Earth's natural environment. Now Earth Day is coordinated globally by the Earth Day Network, and is celebrated in more than 175 countries every year. In 2009, the United Nations designated April 22 International Mother Earth Day. Earth Day is planned for April 22 in all years at least through 2015.

The name and concept of Earth Day was allegedly pioneered by John McConnell in 1969 at a UNESCO Conference in San Francisco. He proposed March 21, 1970, the first day of spring in the northern hemisphere. This day of nature's equipoise was later sanctioned in a Proclamation signed by Secretary General U Thant at the United Nations. About the same time a separate Earth Day was founded by United States Senator Gaylord Nelson as an environmental teach-in first held on April 22, 1970. While this April 22 Earth Day was focused on the United States, an organization launched by Denis Hayes, who was the original national coordinator in 1970, took it international in 1990 and organized events in 141 nations. Numerous communities celebrate Earth Week, an entire week of activities focused on environmental issues.

Earth (or the Earth) is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets. It is sometimes referred to as the world, the Blue Planet, or by its Latin name, Terra.

Earth formed approximately 4.54 billion years ago by accretion from the solar nebula, and life appeared on its surface within one billion years. The planet is home to millions of species, including humans. Earth's biosphere has significantly altered the atmosphere and other abiotic conditions on the planet, enabling the proliferation of aerobic organisms as well as the formation of the ozone layer which, together with Earth's magnetic field, blocks harmful solar radiation, permitting life on land. The physical properties of the Earth, as well as its geological history and orbit, have allowed life to persist. The planet is expected to continue supporting life for another 500 million to 2.3 billion years.

A day is a unit of time, commonly defined as an interval equal to 24 hours. It also can mean that portion of the full day during which a location is illuminated by the light of the sun, also known as daytime. The period of time measured from local noon to the following local noon is called a solar day.

Several definitions of this universal human concept are used according to context, need and convenience. In 1967, the second was redefined in terms of the wavelength of light, and it became the SI base unit of time. The unit of measurement for time called "day", redefined in 1967 as 86,400 SI seconds and symbolized d, is not an SI unit, but it is accepted for use with SI. A civil day is usually also 86,400 seconds, plus or minus a possible leap second in Coordinated Universal Time UTC, and, in some locations, occasionally plus or minus an hour when changing from or to daylight saving time. The word day may also refer to a day of the week or to a calendar date, as in answer to the question "On which day?" Day also refers to the part of the day that is not night — also known as 'daytime'. The life patterns of humans and many other species are related to Earth's solar day and the cycle of day and night (see circadian rhythms).

Henry John Deutschendorf, Jr. (December 31, 1943 – October 12, 1997), known professionally as John Denver, was an American singer/songwriter, activist, and humanitarian. After traveling and living in numerous locations while growing up in his military family, Denver began his music career in folk music groups in the late 1960s. His greatest commercial success was as a solo singer. Throughout his life Denver recorded and released approximately 300 songs, about 200 of which he composed. He performed primarily with an acoustic guitar and sang about his joy in nature, his enthusiasm for music, and relationship trials. Denver's music appeared on a variety of charts including country & western, the Billboard Hot 100, and adult contemporary, in all earning him 12 gold and 4 platinum albums with his signature songs "Sunshine on My Shoulders", "Take Me Home, Country Roads", "Leaving on a Jet Plane", "Rocky Mountain High", "Annie's Song", and "Calypso".

Denver further starred in films and several notable television specials in the 1970s and 1980s. In the following decades he continued to record, but also focused on calling attention to environmental issues, lent his vocal support to space exploration, and testified in front of Congress to protest censorship in music. He is known for his love of the state of Colorado, which he sang about numerous times. He lived in Aspen, Colorado, for much of his life, and influenced the governor to name him Poet Laureate of the state in 1974. The Colorado state legislature also adopted "Rocky Mountain High" as one of its state songs in 2007. He was an avid pilot, and died while flying his personal aircraft at the age of 53. Denver was one of the most popular acoustic artists of the 1970s.

Walter Leland Cronkite, Jr. (November 4, 1916 – July 17, 2009) was an American broadcast journalist, best known as anchorman for the CBS Evening News for 19 years (1962–81). During the heyday of CBS News in the 1960s and 1970s, he was often cited as "the most trusted man in America" after being so named in an opinion poll. Although he reported many events from 1937 to 1981, including bombing in World War II, the Nuremberg trials, combat in the Vietnam War,Watergate, the Iran Hostage Crisis, and the murders of President John F. Kennedy, civil rights pioneer Martin Luther King, Jr., and The Beatles musician John Lennon, he was known for extensive TV coverage of the U.S. space program, from Project Mercury to the Moon landings to the Space Shuttle. He was the only non-NASA recipient of a Moon-rock award. Cronkite is well known for his departing catchphrase "And that's the way it is," followed by the date on which the appearance is aired.

Cronkite was born in Saint Joseph, Missouri, the son of Helen Lena (née Fritsche, August 1892 - November 1993), and Dr. Walter Leland Cronkite (September 1893 - May 1973), a dentist. He had remote Dutch ancestry on his father's side, the family surname originally being Krankheyt.