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Hipparchus was the most important Greek astronomers of his time. He very accurately cataloged over 1,000 stars and invented the mathematical science of trigonometry. Ptolemy was a great admirer of Hipparchus's research and recorded some of it in his book the "Almagest". Hipparchus studied the finding of earlier astronomers and compared them with his own. He discovered the procession of the equinoxes and was able to calculate the tropical year within 6.5 minutes of modern measurements. The tropical year is the length of the year measured by the Sun. Hipparchus devised a method of locating geographic positions by means of latitudes and longitudes which is still in use today....



Hipparchus was the most important Greek astronomers of his time. He very accurately cataloged over 1,000 stars and invented the mathematical science of trigonometry. Ptolemy was a great admirer of Hipparchus's research and recorded some of it in his book the "Almagest". Hipparchus studied the finding of earlier astronomers and compared them with his own. He discovered the procession of the equinoxes and was able to calculate the tropical year within 6.5 minutes of modern measurements. The tropical year is the length of the year measured by the Sun. Hipparchus devised a method of locating geographic positions by means of latitudes and longitudes which is still in use today.... More • http://library.think ... rchus.html
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