Hipparchus (c. 190-120 BC) was the most important Greek astronomer of his time. Hipparchus was extremely accurate in his research, a record that was kept by the astronomer Ptolemy, who was greatly influenced by Hipparchus.

Hipparchus’s calculation of the length of the year measured by the sun was within 6.5 minutes of modern measurements.

Hipparchus devised a method of locating geographic positions by means of latitudes and longitudes.

He cataloged, charted, and calculated the brightness of perhaps as many as 1000 stars.

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