Barbara Bastian, age 13, of Gary, Ind., for her question:
Does the earth ever stand still?
No indeed, the old earth never pauses for a second, or even a fraction of a second. What's more, it is moving in several different directions at once. It spins around on its axis like a top. This is called the earth's rotation. It travels around the sun in a huge circle called its orbit. This is the earth's rotation around the sun. The sun and the whole Solar System are moving with billions of other stars in a great cartwheel called the Galaxy.
The speeds of these different motions are amazing. The earth rotates once in 24 hours less four minutes. First one side and then the other faces the sun and the earth's rotation gives us day and night. Rotation speed at the equator is about 1,000 miles an hour for here the earth has farthest to turn. Going away from the equator the rotation speed is slower and slower. At the poles there is hardly any rotation at all.
Once a year the earth travels a 600 million mile journey around the sun. The average speed for this trip is 182 miles a second, or more than 66,000 miles an hour. The earth and everything on it travel at this staggering speed around the sun day and night.
The great Galaxy is our home in the heavens. It contains all the stars we see in the sky, plus billions more. The stars form a vast system, moving like a wheel. Our own Solar System is about two thirds of the distance from the center of the wheel to the outer rim. The sun and its children the planets roll around with the Galaxy at about 1?0 miles a second, or more than 600,000 miles an hour.
Just the idea of these terrific speeds is enough to make us dizzy. Actually, however, we do not feel them at all. Nor do you feel the speed of a car traveling steadily at 80 miles an hour. In an airplane traveling steadily at 200 or 300 miles an hour you do not feel the speed. This is because we do not notice a steady speed no matter how fast it is. We feel acceleration as we gather speed and we feel deceleration as we lose speed. But steady speed does not affect us.
Suppose you are a passenger in a car traveling at 25 miles an hour. The driver suddenly steps on the brakes. The car stops. You get quite a jolt because your body is jerked forward. It wants to keep on traveling at 25 miles an hour. It has gained speed, or momentum, from the moving car and needs time to stop.
Imagine the momentum we gain from the speeding earth. If the old earth ever put on her brakes we would go flying off into space. But let's not worry. The old earth will never pause, even for a moment.