Hipparchus Greek Astronomer. Considered Greatest Ancient Astronomical Observer. Hipparchus’ precision and astronomical calculations led to his invention of trigonometry and discovery of precession, the compilation of the first Star Catalogue.

Hipparchus (c. 200-126 BC) was a Greek astronomer who worked on the island of Rhodes. Little was known of him; some believe he was probably born in Nicaea, Bithynia, now northwestern Turkey.

Hipparchus is mainly credited for precession, the compilation of the first comprehensive Star Catalogue. It took another three centuries when Ptolemy (Claudius Ptolemaeus) synthesized astronomy that superseded the work of Hipparchus, however, Ptolemy’s work was very much dependent upon the ideas and concepts that were developed by Hipparchus.

Hipparchus estimated the distance from the moon from the earth. He also drew the first accurate star map with more than 1,000 stars that were divided into orders based on their brightness; the fundamentals of this system are in use today.

This ancient Greek thinker also developed an organization of the universe. Although he assumed at that time that the earth was the center, he still provided for accurate prediction of the planets’ positions.

### Hipparchus the Astronomer and Observer

This Greek astronomer was a skilled observer but also drew on the long history of astronomy in the Middle East. In particular, he looked into ancient Babylonian records from the Persian Empire ruins after Alexander’s conquest.

Unusual for the time, Hipparchus spotted a new star (“nova”) in the night sky sometime in 134 BC; an event only followed when Tycho Brahe spotted one in 1572. Inspired by the occurrence, Hipparchus compiled a catalogue of all the 850 stars with known positions. This was the same catalogue that Ptolemy adapted later. It was said to be so accurate that Edmund Halley, of famed Halley’s Comet, was able to compare his own map with Hipparchus’s catalogue almost 2 centuries later.

Hipparchus compared stars by providing each one a magnitude number from one to six, starting from its brightness. For instance *Sirius*, the “Dog Star,” which is the brightest, is called a First Magnitude star, and so on. Present day astronomers still use this concept.

### Hipparchus Precision

His greatest trait was precision in his observation considering he had no telescope and only used his naked eye, and without exact historical records to guide him.

Like the others in his time, Hipparchus made the great mistake in his assumption that the earth is stationary and that the sun, moon, planets and stars revolve around it. Despite this, he was still able to provide calculations with high accuracy.

### Hipparchus Calculations

Today, Hipparchus is regarded as the inventor of trigonometry, the mathematics of triangle. His mathematical skill greatly aligned with his astronomical precision and he developed the chords of the first trigonometrical tables, the tool that aided him in calculating the precise position of a star in relation to the earth and other stars.

Hipparchus and Ptolemy, who followed him, were the greatest ancient astronomers whose work formed the basis of astronomy for almost the next two centuries.

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