How Astronomy Has Developed

The early watchers of the skies picked out groups of stars that seemed to be together in the sky, or that were arranged in shapes that were easy to remember. They called these groups of stars constellations and gave them names, naming them for the gods in their mythology, or for animals or characters in their favorite stories. We still use their ancient names for these constellations. The ancient astronomers saw, too, that most of the stars seemed to move through the skies together, as though they were stuck into the sky as a jewel is embedded in metal.

These they called the “fixed” stars. One of these stars never moved at all, but stayed in one place directly to the north; so this was called the North Star, or the Pole Star, and for thousands of years it has helped navigators to guide their ships at sea. The early astronomers also noticed that five of the “stars” were not fixed. Sometimes they rose in one part of the sky, sometimes in another. These bodies they called planets, meaning “wanderers.” Today we know that these planets are not stars at all.

They are bodies similar to our Earth, and revolve around the sun. There are other planets, but only five can be seen with the naked eye. These are Mercury, Venus, Mars, Jupiter, and Saturn. You can read more about them in the article on the solar system . About a hundred years after the birth of Jesus, an Egyptian scientist named Ptolemy wrote a book called the Almagest in which he set down everything that was then known about astronomy, and also his own ideas on the subject. Ptolemy believed that the Earth was the center of the universe, with the sun and stars revolving around it. We know now that this is not so, but for more than 1,100 years astronomers followed Ptolemy’s teaching. Then a great astronomer named Nicolaus Copernicus, of Poland, challenged Ptolemy’s idea. Copernicus showed that the Earth and the other planets actually revolve around the sun. We know now that this is true.