Hipparchus was an Ancient Greek astronomer and mathematician who made several significant contributions to both subjects. Not only did he compile the first star catalog, and discovered the precession of the equinoxes, he is also considered the founder of trigonometry.
Hipparchus was born in Nicea, in what is now modern day Turkey. It is believed that he was born around 190 BC, although this is an estimate based on clues from his timeline of work. Little else is known about the early life of Hipparchus, such as his education and how his interest in astronomy was formed.
It is known that Hipparchus worked as an astronomer from at least 162 to 127 BC. He spent most of his time working in Rhodes, although he also spent time in Alexandria. During that time, he made great advances in the astronomy field. Through his work and observations, Hipparchus shows a clear dislike for astrology and the popular belief at that time that the Earth was the center of the universe and the sun and moon revolved around it. He also discovered the movement of the measured positions of the stars that resulted from the movement of the ecliptic and celestial equator, known as the precession of the equinoxes. It is not known what tools he used to make this discovery, but it took painstaking work and a sharp mind to discover something so groundbreaking. This discovery led to calculating the length of the year much more accurately.
Hipparchus is also known for the earliest form of trigonometry, due to his studies in astronomy. He formulated a table of geometric chords and developed a method for solving spherical triangles. It is also believed that Ptolemy's Theorem was derived directly from Hipparchus. Other works of Hipparchus includes being the first person to use math principles to determine places along the earth's surface, using latitude and longitude. He also compiled a catalog of all the known stars at the time. Nothing is known of his death, except that he died in about 120 BC.