It is much harder for us to understand the universe as we know it today than it was for ancient man to grasp his idea of the universe. Today we consider the universe to include not only the earth and our solar system. but the galaxy to which this solar system belongs (called the “Milky Way“), and all the other galaxies as well. There are some 200000,000,000 stars in just our own galaxy. and there are millions of other galaxies stretching out into the universe. Man’s imagination just cannot grasp vastness.
But in ancient times, they had a very simple picture of the universe. They thought that the sun, moon, stars, and planets were small objects moving around the earth. They believed that them- with a vast, flat, immovable earth in the centre and a great dome overhead, sprinkled with thousands of little shining lights.
The Greeks started the true science of astronomy. Most of the ancient Greeks thought that the earth stood still in the centre of the universe. Pythagoras, who lived in the sixth century B.C., seems to have been the first to suggest that the earth is a sphere. But he still thought it was the centre of the universe and did not move.
Aristarchus, who lived in the third century B.C., believed the earth was a sphere that rotated on its axis and revolved around a stationary sun. In the second century A.D., an astronomer named Ptolemy wrote a book called the Almagest. He thought the earth was the centre of the universe, and he tried to show how the planets, the sun and the moon moved around the earth. His ideas were accepted for 14 centuries.
Copernicus, in 1543, suggested the sun as the centre of the universe. Then came the discovery of the telescope and man had a better means of finding out what the universe is really like. As more and more facts were gathered, our modern idea of the universe was gradually developed.