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Moon mysteries

Our solitary satellite has already told us a lot about life on Earth – and it has lots more to say

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Power: There's plenty of solar power, as long as you're facing the sun. But you'll be in the sun only half the time unless you put your base near one of the poles. A mountain peak at the moon's south pole is so tall that it gets sunlight all year.

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Radiation: The universe is filled with radioactivity, which scientists say is harmful to human life. Earth's atmosphere protects us from this cosmic radiation. But you would want radiation shielding at a lunar outpost. One possibility is to dig below the moon's surface and build the outpost under a couple of meters of rock. Water can also be an effective radiation shield, if it's deep enough.

The astronauts who explored the moon had no special radiation shielding, but they were only in space for a week to 10 days. Such short stays are considered safe.

Gravity: The moon is about 2,155 miles across, one-quarter the size of Earth. It has only one-sixth the gravity. If you weigh 60 pounds on Earth, you'd weigh only 10 pounds on the moon. This may sound like fun, but scientists aren't sure what the health effects might be. Exercise may be key.

Location: An outpost on the side facing the Earth would be able to communicate easily with the home planet. But if you want to study the stars, a base on the far side would be free from all the "light pollution" of Earth. Radiotelescopes could also operate there, away from the "noise" of radio and TV signals.

More: A lunar outpost would give humans opportunities to explore the moon, mine its minerals, get a clearer view of the universe, and help us learn more about living in space. What other activities would you plan at your lunar outpost? How would the people there carry them out? Would robots or remote-control machines play a role?

Sketch your own lunar outpost and describe how it would function. Perhaps someday you can compare your idea to the real thing.

Do you know of a 'moon tree' near you?

When Apollo 14 went to the moon in February 1971, Stuart Roosa was the command-module pilot. He orbited the moon while Alan Shepard and Edgar Mitchell explored the surface. Roosa, a former "smoke jumper" (a firefighter who parachutes in to fight forest fires), took some 450 tree seeds with him on the flight. When he returned to Earth, the seeds were planted. The loblolly pine, sycamore, sweetgum, redwood, and Douglas fir trees became known as "moon trees."

These trees were sent all over the world as a living monuments to the Apollo program and to Roosa, who died in 1994. But no complete list was kept of where all the trees were sent. Information on known trees and their locations can be found at this website: But if you know of a moon tree that's not on the list, NASA would like to hear from you. Send your message to

Lunar websites

You can find stories, puzzles, and moon information at:

Learn about lunar explorations, Apollo missions, and 'moon trees' at:

Check out moon maps, pictures of the moon, and quizzes at:

See views of the moon as it looks through binoculars, telescopes, and from space at:

Why the moon has phases

The moon takes 29-1/2 days to go around the Earth. The phases of the moon are the result of our observing the moon in different parts of its orbit.

The sun always shines on half the moon, just as it shines on half the Earth. (See diagram below.) Because we can see only the side of the moon that's facing Earth, it appears that the moon is only partly lit sometimes. That's because we can't see all of the lit-up half of the moon.

The moon rises and sets at different times during the month, but don't be fooled: It's the Earth turning, not the moon orbiting, that's most responsible for moonrise and moonset. We spin past the moon much faster than it orbits around us.

One more thing: The moon turns on its axis once every 29-1/2 days, too. That's why we always see the same side of it.