# Who is the founder of trigonometry 1

## Hipparchus of Nicaea

Hipparchus (180 - 125 BC) is best known for his contributions to astronomy. For example, he determined the duration of a year to within 6.5 minutes, the inclination of the ecliptic, i.e. the angle between the annual solar orbit and the celestial equator, the annual precession of the equinox, i.e. the intersection between the solar orbit and celestial equator, to 46 '' (modern Value: 50.26 ''), the parallax of the moon and the eccentricity of the sun's orbit. He observed a nova for the first time in Europe and knew that the moon was only approximately in a circular orbit and suggested epicycles as a better approximation for its orbit (and the orbits of the planets).

Hipparchus also put together the most extensive star catalog of antiquity, in which 1080 fixed stars were recorded in 49 constellations, which he already divided into 6 size classes, and which the British astronomer Halley still used. In contrast, only 1022 fixed stars appear in the *Almagest* of Ptolemy.

Hipparchus was the founder of the *trigonometry*, and, as an aid for his astronomical calculations, set up the first table for the chord length in a circle as a function of the central angle *Chord board*. Here he used formulas that we would write today as addition theorem for the sine and in the form, but without explicitly knowing these trigonometric functions. From the Babylonians he took over the sexagesimal system, which has been preserved to this day in the degree measurement, in which a full circle in (degrees),

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