Moon summary

Apollo, project conducted by the U.S. National Aeronautics and Space Administration (NASA) in the 1960s and ’70s that landed the first humans on the Moon. All told, 24 Apollo astronauts visited the Moon and 12 of them walked on its surface. Additional NASA astronauts are scheduled to return to the

Tide, any of the cyclic deformations of one astronomical body caused by the gravitational forces exerted by others. The most familiar are the periodic variations in sea level on Earth that correspond to changes in the relative positions of the Moon and the Sun. The tides may be regarded as forced

Solar system, assemblage consisting of the Sun—an average star in the Milky Way Galaxy—and those bodies orbiting around it: 8 (formerly 9) planets with more than 400 known planetary satellites (moons); many asteroids, some with their own satellites; comets and other icy bodies; and vast reaches of

Earth, third planet from the Sun and the fifth largest planet in the solar system in terms of size and mass. Its single most outstanding feature is that its near-surface environments are the only places in the universe known to harbour life. It is designated by the symbol ♁. Earth’s name in