Michael Furtado, age 11, of Santa Maria, California, for his question:
Why don't we ever see the other side of the moon?
The same old face of the moon has been gazing down on the earth since time began. People guessed, but nobody was certain what the opposite side looked like. Then came the Space Age, and on October 7, 1959, a man made satellite relayed the first pictures of the other side of the moon back to earth.
Today's problem can be compared to a type of dance. Styles of dancing, of course change with the times and the popular frug cannot be twisted around to clarify the picture we need. But the old style country dancing is just right for the job. In every boisterous hoedown, there comes a proper time to swing your partner. You join hands and swing each other around in a circle. During this merry maneuver, you keep your face turned toward your partner. But notice meantime that both of you move around in a complete circle. All the celestial bodies are constantly swinging around in complicated heavenly hoedowns of this sort.
The moon and the earth are swinging partners but the moon does most of the swinging. The center of the circuit is the half way mark between their combined weights or masses. This focal point happens to be about 1,000 miles below the earth's surface. Hence the more massive earth merely sways a little while the lightweight moon swings in orbit around its partner.
Since the same face of the moon is frozen in our direction, we tend to think that the moon does not rotate on its axis. But this is not true. Both partners in our hoedown rotate, but at vastly different rates. The earth, of course, makes a complete rotation every calendar day, while the moon spins only once on its axis during each orbital swing around the earth. The mom's rotation time exactly equals the time of its revolution a period of roughly 27 1/3 days. In square dance terms this means that the moon turns just enough to keep facing its partner as it makes one complete swing around him.
These celestial movements are dictated by the cosmic force of gravitation. Every speck of dust in the universe has a quota of this built in force of attraction. More massive bodies have more of it. Gravitation increases in precise ratio when more matter is packed into a celestial body. And its pulling power decreases with distance at an exact ratio. The earth is almost four times bigger than the moon and its denser material is more than one third heavier. These factors endow it with far more pulling power. The mightier gravity of our planet holds the moon in a captive orbit and keeps the same side of its satellite always turned to face us.
The modern Space Age ended the long ages when the moon was an untouchable object across an impassable stretch of celestial space. Soon men will land for the first time on the lunar landscape. There they will come to grips with its lighter gravity. Everything will weigh only one sixth as much as it weighs on the surface of our big, heavy planet. Earth trained muscles will be six times stronger. A six-foot leap on earth will equal a 36-foot leap on the moon.