Benson Habib, age 11, of Atlanta, Georgia, for his question:
In what direction are we traveling through space?
Astronomers sometimes refer to the planet Earth as a spaceship. When you learn how our world is bowling through the heavens, this seems to be true. However, one would expect a man made spaceship to be going somewhere, perhaps aiming to reach the planets of another star. The Spaceship Earth seems to have no particular destination, for it spins and whirls through the sky in never ending circles.
Most of the members of our solar family are eastward bound. The earth rotates on its axis toward the east. So do most of the other planets, the moon and also the sun. The earth orbits the sun in an easterly direction. So do all the other planets. Our moon orbits east¬ward around the earth and most of the other moons also orbit their planets in an easterly direction.
At home in the Solar System, the most popular direction is eastward bound. What is more remarkable is the fantastic speeds at which the Spaceship Earth is moving. The big round ball spins once around its axis every 24 hours. This means that at the equator the surface rotation speed is more than 1,000 miles per hour.
Our orbital speed around the sun is estimated to be 18 miles per second. The average speed of this never ending eastbound journey is 66,000 miles per hour. In one year we dwellers on the Spaceship Earth travel an orbital distance of 595 million miles. True, we never seem to go any place because each orbital spin brings us back to where we started—or so it seems.
Actually, the whole Solar System is bowling through the starry heavens at an even more fantastic speed. All the members of our solar family travel together as a unit, each maintaining its local motions. But with every yearly orbit around the sun, we are millions of miles farther along an enormous path through the Galaxy.
The Galaxy is an enormous, cart wheeling star system. Our sun is but one of its 100 billion stars and goodness knows how many other solar systems belong in the system. We are located about three fifths of the way from the star crowded center. Stars closer to the center wheel around faster than we do and those toward the outer rim swing around more slowly.
And, of all things, the starry Galaxy also swings around toward the east, the same direction in which the Earth spins on its axis and orbits the sun. However, the size of our orbit through the Galaxy is stupendous and its galactic orbital speed is fantastic. The Earth, along with the orderly Solar System, is traveling through the starry Galaxy at an estimated speed of 43,000 miles per hour.
Day and night, year in and year out, the dizzy old earth continues its speeding, eastward bound voyages through space. Even so, the Galaxy is so enormous that it takes us about 200 million years to complete one galactic orbit. This period is the cosmic year. Since the earth was formed, it has had time to complete only about 25 of these cosmic years traveling eastward at 43,000 miles per hour.