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About Astronomy
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Short Description: make the most detailed map in the history of astronomy, a map that ... In two thousand years of astronomy, no one ever guessed that the universe might be ...
Content Inside: About Astronomy Gazing up at the sky on a clear moonless night, you can see about two thousand stars. In the 2nd century B.C., Hipparchus, an ancient Greek astronomer, gazed at the sky and saw the same stars. Hipparchus spent years carefully observing the stars, and he became one of the first people to make a map of the sky. Using his map, together with observations made by the ancient Babylonians, he discovered that if you look at the positions of the stars on the first day of spring every year, they will have shifted slightly from the year before. His discovery ranks as one of the greatest discoveries in the history of astronomy. But he could not have made it without his map. Today, astronomers are on the verge of many other exciting discoveries. They have found objects called quasars, the size of the Solar System but brighter than an entire galaxy, that are the most distant objects in the universe. They have found faint failed stars called brown dwarfs, a missing link in the evolution of stars. And they are constructing a map of the entire universe that might shed light on the universe's origins fifteen billion years ago. But like Hipparchus, modern astronomers cannot continue to make these discoveries without an accurate map. Over the next few years, the Sloan Digital Sky Survey will make the most detailed map in the history of astronomy, a map that astronomers will use for decades to come. The History of Sky Surveys Sky surveys have had a long history, and have led to some of the most important discoveries in astronomy. The next major systematic sky survey was not begun until 1700 years after Hipparchus. Tycho Brahe, a 16th Century Danish nobleman, studied the motions of the planets from an observatory on his property. Brahe and his assistants made naked eye observations with the help of a large sextant, a tool that sailors used to find stars. Brahe's survey took decades, and was more precise than any survey before. After Brahe died, data from his survey was passed on to his assistant, Johannes Kepler. Using Brahe's data, Kepler deduced that all the planets travel around the Sun in elliptical orbits - forever laying to rest the idea that the Earth was at the center of the universe - and derived his famous three Tycho Brahe's observatory laws of planetary motion. Kepler's work, based entirely on Brahe's map, stands as one of science's crowning intellectual achievements. For three hundred years after Kepler's time, astronomers thought the universe consisted of only the stars in our the Milky Way, along with a handful of faint, fuzzy, and mysterious objects they called "nebulae." Most astronomers believed these objects were interspersed among the stars. Later, it was found that most of these objects were actually
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