Lisa Clark, age 11, of Columbus, Ohio, for her question:
WHY CAN YOU SOMETIMES SEE THE MOON DURING THE DAY?
When you see the moon shining in the night sky, it isn't shining at all but is only reflecting or casting back light from the sun. The moon gives off no light of its own.
You are able to see the dim moon at certain times during the day if you know where to look. The reason you can see it is because it is throwing back a dim reflection from the sun. When the sky becomes dark, the reflected light of the moon is easier to spot.
The moon rises and sets at different times. In the new moon phase, when the moon is between the sun and the Earth and its sunlit side is turned away from the earth, the moon rises above the horizon with the sun in the east and travels close to the sun across the sky. During this period, you can't see even a faint outline of the moon during the day.
With each passing day, the moon rises an average of about 50 minutes later and drops about 12 degrees farther behind in relation to the sun. By the end of a week, at the first quarter phase, the moon rises at about noon and sets at about midnight.
A week after the first quarter comes the full moon. It rises as the sun sets and sets as the sun rises.
At the last quarter, the moon rises at about midnight and sets at about noon. During this period, especially, it is easy to see the moon during the morning hours in the western sky.
Then a week later, the moon goes back into its new moon phase.
The rotation period of the moon around the Earth is 29 days, 12 hours and 44 minutes.
The moon moves at an average speed of about 2,300 miles per hour along its 1.4 million mile orbit. The moon also travels with the Earth as the Earth circles the sun every 365 and a quarter days.
The moon moves from west to east in the sky but it seems to move from east to west as it rises and sets because the Earth spins much faster than the moon revolves around the earth.
The length of day and night on the moon is about 14 Earth days each.
Two forces hold the moon in its orbit: gravity, which tries to pull the Earth and the moon toward each other, and centrifugal force, which tries to pull the moon away from the Earth and throw it farther into space.
The moon's revolution around the Earth is measured in synodic and sidereal months. A synodic month of about 29 1/2 days is the period from one new moon to the next, or the time it takes the moon to revolve around the Earth. A sidereal month is the time the moon takes to make one trip around the Earth in relation to the stars as seen from the center of the Earth.
The moon appears to be much larger than all of the stars and about the same size as the sun. This isn't the case, however, but just appears this way because the moon is so close to the Earth.
On July 20, 1969, American astronaut Neil Armstrong became the first person to set foot on the moon, the Earth's nearest neighbor in space. He confirmed what scientists had already told us: There is no life on the moon.