Sunday, April 16, 2006

Hipparchus of Rhodes

Hipparchus is considered by many to be the father of trigonometry because he was the first to organize measurements in relation to angles in a trigonometric table. Unfortunately, all but one of his math writings have been lost and the one text that remains is a minor work. Most of what we know today comes from the Greek astronomer Ptolemy.

Hipparchus was born around 190 B.C. in the town of Nicaea and died around 120 B.C. in Rhodes. He may have studied geometry in Alexandria. Unfortunately, not much more is known about his life.

His influence on astronomy and mathematics has been significant. He produced the first trigonometric table based on chords (the table lists the length of the chord that corresponds to a given angle). He discovered the precession of the equinoxes and accurately determined the length of a year to within 6.5 minutes. It is believed that Hipparchus created the first star catalogue which may have consisted of 650 stars. It is believed that he created this around 134 B.C. when a new star was said to have burst across the sky.

He was able to calculate the distance of the moon from the earth and developed a theory of the moon's motions based on epicycles. He also used epicycles to model the Sun's motions. He was perhaps the first to be able to predict solar and lunar eclipses. Hipparchus may have invented the astrolabe and used an equatorial ring to observe the sun's equinoxes.

Most of what is known about Hipparchus is found in Ptolemy's magnus opus Almagest. It was not Ptolemy's intentions to preserve the memory of Hipparchus. In fact, Ptolemy seems to assume that his reader has access to Hipparchus's original works.


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