The moon is a satellite of Earth. A satellite is an object in space that moves around another object. The moon revolves around the earth in an orbit. It moves about 3700 kilometers per hour in a west to east direction. The moon seems to rise from east and set in the west (like the sun). The reason for this is that Earth rotates from west to east much faster than the moon revolves around it. The moon stays in orbit as it revolves around Earth because Earth’s gravity pulls at it. It takes the moon 29 ½ days to revolve around Earth. The period it takes the moon to complete one revolution is called a month. Like earth, the moon also rotates on its axis from west to east. As the moon completes one revolution around Earth, it also completes one rotation on its axis.

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Look for a spot on the moon that you can easily find. Observe the moon for a few minutes for several days. Can you find the spot you have chosen? What does this show? The spot you have chosen is a moon landmark. As the moon turns, the landmark stays in the same position. This shows that you are seeing the same side of the moon. When we look at the moon, we always see the same side because, in the same time that the moon revolves around Earth, it rotates only once on its axis.

Why the Moon’s shape seems to change? The moon revolves around Earth as its axis. It takes the moon 29 ½ days to complete one revolution. During this time, it seems to take on different shapes. The moon travels with Earth around the sun. Half of the moon is always lighted by the sun. The light of the moon the shines on Earth is reflected sunlight. As the moon revolves around the earth, it reflects different amounts of sunlight to earth. When the moon is between the sun and earth, we cannot see the lighted side of the moon. What we see is the dark outline of the moon. This is called new moon. A day after the new moon, we see a thin slice of light at the edge of the moon. This is called crescent moon. About a week after the new moon, we see half of the lighted side of the moon. This is called first quarter moon. As the first quarter moon increases in size, it is called gibbous moon. About a week after the first quarter moon, the earth is between the moon and the sun. We can see the whole lighted side of the moon. This is called full moon. The full moon decreases in size until it is again a gibbous moon. About a week after the full moon, we again see half of its lighted part. This is called last quarter moon. After this, the lighted part becomes smaller until we see a crescent moon. Soon the moon becomes invisible, after which another new moon appears.

The moon does not change in shape. It only seems to change in shape because, as it revolves around the Earth, the lighted part that we see increases or decreases in size. As the moon moves from new to full, it is said to be waxing. This means that the lighted part we see increases in size. As the full moon moves to new moon, it is said to be waning. This means that the lighted part we see decreases in size. The apparent changes in the shape of the moon that we see is called phases of the moon. The moon goes through these phases is 29 ½ days.

The moon rises and sets at different times. In the new moon phase, the moon rises with the sun. in days that follow, it rises later than the sun. in the first quarter phase, it rises at noontime and sets at midnight. During the full moon, it rises at the time the sun rises. During the last quarter it rises at midnight and sets at noontime.