San Yung Oh, age 12, of Winnipeg, Manitoba, Canada, for his question:
WHY DOES THE SAME SIDE OF THE MOON ALWAYS FACE THE EARTH?
The moon is our closest celestial neighbor, being anchored in space just 238,857 miles from the earth. That's a long distance, but it sounds almost like just across the international border when you compare it to the distance between earth and the sun and come up with more than 93 million miles.
Our closest space neighbor always turns the same face to us because the moon rotates in exactly the same length of time that it takes to revolve about the earth. For this reason, we can only see one side.
But how, you ask, is this possible since the moon also rotates?
Do this to prove the point: stand in your room and face north. Several feet in front of you, place any object such as a book. The book will represent the earth and you will represent the moon.
Now start walking around the book slowly, keeping your face toward it. Go all the way around. In turn you will be looking east, south, west and back to north. You will have revolved and yet your face has always been toward the book.
This is just what happens when the moon rotates around the earth. And now you know why we always see the same side of the moon.
The time it takes the moon to revolve around the earth is 29 days, 12 hours and 44.05 minutes. It is actually a natural satellite of the earth.
The moon has three kinds of motion. First of all, it revolves around the earth. In addition it rotates on its axis and it also follows the earth in a journey around the sun.
The moon's shape seems to change from night to night as we observe it from earth. These changes are called phases of the moon. We can see the full moon shining when earth is between the moon and the sun. When the moon is between earth and the sun, the lighted half is turned completely away from the earth. Then the moon cannot be seen. During the time that the moon is between these two positions, only portions of the lighted moon are seen from earth.
As the moon goes from new moon to full, its shape grows larger and we call this the waxing period. As it goes from full back to new, we call this waning. During the waning period the moon's shape gets smaller. When the moon is waxing the right portions of the moon appear to be lighted. When the moon is waning, the light is on the left portions. The waxing quarter phase is called the first quarter. The waning quarter phase is the third quarter.