The moon is the only natural satelliteorbiting Earth and the Earth's closest neighbor in space. This cold, rocky body is about 384,403 kilometers (238,857 miles) away. This distance is similar to going around the earth 10 times.
The moon is 3,476 kilometers (2,160 miles) in diameter. It is 1/4 the size of the earth. It is about 400 times smaller than the sun and 400 times closer. For this reason the sun and moon appear to be the exact same size.
The moon is very old!!! Scientists believe that about 4.5 billion years ago a Mars-sized body hit Earth and the resulting debris (from both Earth and the impacting body) accumulated to form the Moon. Scientists know this because they studied the lunar rocks that were collected by astronauts who went to the moon. The moon and the earth are made of the same material.
You can read more about the moon at NASA's StarChild, a Learning center for Young Astronomers.
What's it like on the Moon?
The daily maximum temperature is 250° F (hot enough to boil water). At night the temperature can reach -250° F.
The moon has no atmosphere, so the lunar sky is black. You need atmosphere to make the sky blue. Astronauts must carry their own air for breathing when they visit the moon. Funny stuff: Did you hear the one about the restaurant on the moon? The food is terrific, but there's no atmosphere!
The surface of the moon is covered in craters or holes that have been created by space rocks or meteors that hit the soil. The lack of atmosphere there allows the rocks to crash into the surface. An atmosphere like the Earth's would prevent most meteors from reaching the surface because friction would burn them up.
No rivers, lakes or oceans exist on the moon. But evidence gathered by some exploration missions — Lunar Prospector (1998-1999), Chandrayaan-1 (2008-2009), and the Lunar Crater Observation and Sensing Satellite (LCROSS; 2009) — strongly suggest that water, in the form of ice, exists at both the Moon's north and south poles. Both areas have deep and permanently shaded craters that help trap the ice and prevent it from vaporizing into space.
If you weigh 60 pounds on earth, you would weigh 10 pounds on the moon because gravity is 1/6th as strong on the moon.
The Far Side of the Moon
The same side of the moon always faces Earth. This means that when we look up into the sky we can only see one side.
Below is a NASA photo of the far side of the moon. Until humans sent spacecraft around the moon, no one had seen this side of our neighbor.
The moon has no light of its own. It shines because sunlight is reflected off its surface.
What is "moonrise"? The Earth rotates once a day on its axis, which makes it appear as if the moon rises over the eastern horizon and sets over the western one. Sunrise and sunset are the same kind of phenomena. NASA has a great photo.
Phases of the Moon
The moon orbits, or revolves, around the Earth about once every 27 days, 7 hours, 43 minutes. This movement causes the moon to cycle through a series of phases: New, New Crescent, First Quarter, Waxing Gibbous, Full, Waning Gibbous, Last Quarter, Old Crescent and back to New again.
Sometimes the moon passes through some portion of the earth's shadow and the Earth blocks part or all of the sun's rays from reaching the moon. This is called a lunar eclipse and can only occur at Full Moon. A schedule of upcoming lunar eclipses can be found on NASA's website.
Almost three hundred sixty years after the Italian astronomer Galileo Galilei made his first observation of the moon with a telescope in 1610, astronauts from the Apollo 11 mission were the first humans to walk on the moon and return rock samples in 1969.
Don't miss the great Apollo 11 story from NASA complete with audio, video, and photos. And here is a chronology of man's lunar visits, starting with the USA's and USSR's first missions in the late 1950s.
NASA's six Apollo missions brought back 381 kilograms (840 pounds) of soil and rock from the moon. The USSR's three unmanned Luna missions brought back an additional 326 grams (11.5 ounces) of material.
This photo (right) offers a close-up view of an astronaut's footprint in the lunar soil. Find more moonwalk photos at this NASA site.