56 Facts About Hipparchus

Hipparchus is considered the founder of trigonometry, but is most famous for his incidental discovery of the precession of the equinoxes.

Hipparchus was born in Nicaea, Bithynia, and probably died on the island of Rhodes, Greece.

Hipparchus is considered the greatest ancient astronomical observer and, by some, the greatest overall astronomer of antiquity.

Hipparchus was the first whose quantitative and accurate models for the motion of the Sun and Moon survive.

Hipparchus developed trigonometry and constructed trigonometric tables, and he solved several problems of spherical trigonometry.

Hipparchus is sometimes called the "father of astronomy", a title first conferred on him by Jean Baptiste Joseph Delambre.

Hipparchus obtained information from Alexandria as well as Babylon, but it is not known when or if he visited these places.

Hipparchus is believed to have died on the island of Rhodes, where he seems to have spent most of his later life.

Hipparchus made a list of his major works that apparently mentioned about fourteen books, but which is only known from references by later authors.

The first trigonometric table was apparently compiled by Hipparchus, who is consequently now known as "the father of trigonometry".

Hipparchus seems to have been the first to exploit Babylonian astronomical knowledge and techniques systematically.

Eudoxus in the 4th century BC and Timocharis and Aristillus in the 3rd century BC already divided the ecliptic in 360 parts of 60 arcminutes and Hipparchus continued this tradition.

However, Franz Xaver Kugler demonstrated that the synodic and anomalistic periods that Ptolemy attributes to Hipparchus had already been used in Babylonian ephemerides, specifically the collection of texts nowadays called "System B".

Hipparchus was recognized as the first mathematician known to have possessed a trigonometric table, which he needed when computing the eccentricity of the orbits of the Moon and Sun.

Hipparchus tabulated values for the chord function, which for a central angle in a circle gives the length of the straight line segment between the points where the angle intersects the circle.

Hipparchus could have constructed his chord table using the Pythagorean theorem and a theorem known to Archimedes.

Hipparchus was the first to show that the stereographic projection is conformal, and that it transforms circles on the sphere that do not pass through the center of projection to circles on the plane.

Besides geometry, Hipparchus used arithmetic techniques developed by the Chaldeans.

Hipparchus was one of the first Greek mathematicians to do this and, in this way, expanded the techniques available to astronomers and geographers.

Hipparchus studied the motion of the Moon and confirmed the accurate values for two periods of its motion that Chaldean astronomers are widely presumed to have possessed before him.

Hipparchus used the multiple of this period by a factor of 17, because that interval is an eclipse period, and is close to an integer number of years.

Hipparchus is the first astronomer known to attempt to determine the relative proportions and actual sizes of these orbits.

Hipparchus devised a geometrical method to find the parameters from three positions of the Moon at particular phases of its anomaly.

Hipparchus used two sets of three lunar eclipse observations that he carefully selected to satisfy the requirements.

Hipparchus found inconsistent results; he later used the ratio of the epicycle model, which is too small.

Hipparchus used old solstice observations and determined a difference of approximately one day in approximately 300 years.

Hipparchus's solution was to place the Earth not at the center of the Sun's motion, but at some distance from the center.

Hipparchus undertook to find the distances and sizes of the Sun and the Moon.

Hipparchus measured the apparent diameters of the Sun and Moon with his diopter.

Hipparchus thus had the problematic result that his minimum distance was greater than his maximum mean distance.

Hipparchus was intellectually honest about this discrepancy, and probably realized that especially the first method is very sensitive to the accuracy of the observations and parameters.

Hipparchus's results were the best so far: the actual mean distance of the Moon is 60.3 Earth radii, within his limits from Hipparchus's second book.

Apparently Hipparchus later refined his computations, and derived accurate single values that he could use for predictions of solar eclipses.

Hipparchus must have been the first to be able to do this.

We do not know what "exact reason" Hipparchus found for seeing the Moon eclipsed while apparently it was not in exact opposition to the Sun.

Hipparchus is credited with the invention or improvement of several astronomical instruments, which were used for a long time for naked-eye observations.

Hipparchus applied his knowledge of spherical angles to the problem of denoting locations on the Earth's surface.

Hipparchus wrote a critique in three books on the work of the geographer Eratosthenes of Cyrene, called Pros ten Eratosthenous geographian.

Hipparchus apparently made many detailed corrections to the locations and distances mentioned by Eratosthenes.

Late in his career Hipparchus compiled his star catalog.

Hipparchus constructed a celestial globe depicting the constellations, based on his observations.

In Raphael's painting The School of Athens, Hipparchus is depicted holding his celestial globe, as the representative figure for astronomy.

Hipparchus is conjectured to have ranked the apparent magnitudes of stars on a numerical scale from 1, the brightest, to 6, the faintest.

Ptolemy's catalog in the Almagest, which is derived from Hipparchus's catalog, is given in ecliptic coordinates.

Hipparchus probably marked them as a unit on his celestial globe but the instrumentation for his observations is unknown.

Delambre in his concluded that Hipparchus knew and used the equatorial coordinate system, a conclusion challenged by Otto Neugebauer in his A History of Ancient Mathematical Astronomy.

Hipparchus seems to have used a mix of ecliptic coordinates and equatorial coordinates: in his commentary on Eudoxus he provides stars' polar distance, right ascension, longitude, polar longitude, but not celestial latitude.

Hipparchus's celestial globe was an instrument similar to modern electronic computers.

Hipparchus compared the lengths of the tropical year and the sidereal year, and found a slight discrepancy.

Hipparchus insists that a geographic map must be based only on astronomical measurements of latitudes and longitudes and triangulation for finding unknown distances.

In geographic theory and methods Hipparchus introduced three main innovations.

Hipparchus was the first to use the grade grid, to determine geographic latitude from star observations, and not only from the Sun's altitude, a method known long before him, and to suggest that geographic longitude could be determined by means of simultaneous observations of lunar eclipses in distant places.

Hipparchus opposed the view generally accepted in the Hellenistic period that the Atlantic and Indian Oceans and the Caspian Sea are parts of a single ocean.

Hipparchus's ideas found their reflection in the Geography of Ptolemy.

Hipparchus was in the international news in 2005, when it was again proposed that the data on the celestial globe of Hipparchus or in his star catalog may have been preserved in the only surviving large ancient celestial globe which depicts the constellations with moderate accuracy, the globe carried by the Farnese Atlas.

Hipparchus was inducted into the International Space Hall of Fame in 2004.