Science Source ftp Apr 2015

Hipparchus in his observatory in Alexandria. In the center is an armillary sphere (spherical framework of rings, centered on Earth, that represent lines of celestial longitude and latitude and other astronomically important features such as the ecliptic). Hipparchus (190-120 BC), was a Greek astronomer, geographer, and mathematician of the Hellenistic period. A methodical observer, Hipparchus compiled the first known star catalogue, listing some 850 stars, as well as their celestial coordinates and magnitude. His work profoundly influenced that of Ptolemy. He is considered the founder of trigonometry. Hipparchus is considered the greatest ancient astronomical observer. He was the first whose quantitative and accurate models for the motion of the Sun and Moon survive. He developed trigonometry and constructed trigonometric tables, and he solved several problems of spherical trigonometry. With his solar and lunar theories and his trigonometry, he may have been the first to develop a reliable method to predict solar eclipses. His other reputed achievements include the discovery of Earth's precession (precession of the equinoxes is a slow motion of the place of the equinoxes through the zodiac, caused by the shifting of the Earth's axis) and possibly the invention of the astrolabe and the armillary sphere.