This image, computer generated from satellite data, shows the striking contrast between the daylight and nighttime hemispheres of Earth. The day side reveals little evidence of human presence, but at night our presence is revealed by the lights of human activity (mostly from cities as well as from agricultural, oil, and gas fires). (From the Voyage scale model solar system, developed by Challenger Center for Space Science Education, the Smithsonian Institution, and NASA. Image created by ARC Science Simulations © 2001.)		This famous photograph shows astronaut Buzz Aldrin standing on the Moon in July 1969 during the Apollo 11 mission. The reflection in his visor shows Neil Armstrong and the lunar module (spacecraft), along with some scientific equipment. Aldrin and Armstrong were the first of 12 humans who walked on the Moon; Armstrong took the first step, saying, "That's one small step for [a] man, one giant leap for mankind."

Beyond Venus and only about 15 meters from the model Sun, we find our home planet. Its tiny size in a big solar system reminds us that Earth is a rare and precious oasis of life. It is the only planet with oxygen for us to breathe and ozone to shield us from deadly solar radiation. Only on Earth does water flow freely to nurture life. And temperatures are ideal for life because Earth's atmosphere contains just enough carbon dioxide and water vapor to maintain a moderate greenhouse effect.

Despite its small size, Earth is striking in it beauty. Blue oceans cover nearly three-fourths of the surface, broken by the continental land masses and scattered islands. The polar caps are white with snow and ice, and white clouds are scattered above the surface. At night, the glow of artificial lights clearly reveals the presence of an intelligent civilization.

Earth is the first planet on our tour with a moon. On our model scale, the Moon is barely visible speck that orbits the Earth at a distance of about 4 centimeters. Thus, your thumb could easily cover both the Earth and the Moon. The Moon is cratered and desolate, much like Mercury. though it has its own interesting history and geology. It is also the only world besides Earth on which humans have ever stepped. From July 1969 through December 1972, NASA's Apollo program successfully landed 12 people (six crews of two) on the lunar surface.

This map shows Earth's location in the Voyage scale model solar system on the National Mall in Washington, DC. The dot at the top of the page (next to title) shows Earth's size on the scale.