Hipparchus of Nicaea ( Ἴππαρχος, dt Hipparchus, * 190 BC in Nicaea; † around 120 BC in Rhodes probably) was the most important Greek astronomer of his time. He is regarded as the founder of scientific astronomy and was also a mathematician and geographer. Him a Astrometriesatellit Hipparcos (High Precision Parallax Collecting Satellite ) was named in honor.
Hipparchus was going on with the utmost accuracy in his research. When comparing his own heaven to those of previous studies (also Babylonian ) astronomers, such as Aristyllos and Timocharis, Hipparchus discovered the precession of the Earth's axis by means of the slow shift of the equinoxes. His calculation of the tropical year ( the length of the particular seasons of the year ) deviates only 6.5 minutes of modern measurements. Hipparchus devised a method to determine positions on Earth using the latitude and lengths. He cataloged and calculated the brightness of about 900 stars and drew them on a map. Hipparchus also presented a table of trigonometric tendons together ( Chordentafel ), which formed the basis of modern trigonometry.
Life and complete works
The best ancient source to Hipparchus, the Alexandrian astronomer Ptolemy 's Almagest. More information can be found in the works of Pappus of Alexandria and Theon of Alexandria in the 4th century, in the " Geography " of Strabo and the " Naturalis historia " Pliny the Elder in the 1st century.
The survival data Hipparchus ' are unknown, but in the Almagest observations have been handed down by him from the years 147-127 BC. Jean Baptiste Delambre calculated from these and other evidence by Birth about 190 BC, in all probability, at Nicaea in Bithynia. Also indirect considerations lead to a death date to 120 BC There are no contemporary portraits known; antique coins with his image were minted only in the 2nd and 3rd centuries in Bythnien. Since it is known by Ptolemy, that Hipparchus observed from Rhodes, taking the island as a place of death.
Also Hipparchus ' main works are lost. Only a critical commentary in two books about a famous poem of Aratus of Soli is obtained. From later mentions it can be concluded that Hipparchus himself has also written a bibliography of his major works, which consisted of approximately 14 works. His star catalog is incorporated into the catalog of the Almagest, but Ptolemy mentions the sources of the measurements are not individually and sometimes not at all. Nevertheless, Hipparchus ' catalog are indirectly restored at least in broad terms, as the acquired measurements of Hipparchus by a common systematic error caused by the precession between Hipparchus ' ' distinguished work and Ptolemy.
Based on his measurements Hipparchus has made a celestial globe. Although here the original is lost, it is known that this world is copied. A copy of such copy could rest on the shoulders of Atlas in the Farnese collections that represents one of the oldest surviving celestial globes.
Hipparchus is considered the father of scientific astronomy and is considered, along with Ptolemy and Aristarchus of Samos, one of the greatest astronomers of antiquity.
The lunar crater Hipparchus is named after him.
By comparing the position of the main star of Virgo, Spica, with about 150 years previously observed positions he discovered the precession of the equinoxes, which had shifted by about 2 °. Members, resulting Hipparchus this precession of Earth's axis of at least one degree per century; the actual value is at a degree per 72 years. Both the temperature measured by Hipparchus and the earlier position had been determined at lunar eclipses. There was very well known by the Babylonian observations between lunar eclipses elapsed time, Hipparchus concluded that the background of the sky must have moved. He calculated the distance between Earth and the Moon ( Lunar Distance) on 30 the diameter of Earth ( 384,000 km ).
Timocharis of Alexandria and Aristyllos had already BC a compilation of star positions recorded at 300, which, however, was probably incomplete. In the year 135 BC there appeared a new star, possibly a supernova. Since the sphere of fixed stars was considered eternal, hid such new stars explosiveness (as well as in times of Tycho Brahe ). Hipparchus decided to create a more complete star catalog, which must have included approximately between 800 and 1000 stars. The catalog itself is not known, but it is considered very likely that Ptolemy at least partially took over Hipparchus ' positions in the Almagest and corrected for the accumulated precession. Since the precession was only imprecisely known, groups of presumably older measurements in the Almagest to be identified.
The length of the seasons
The different lengths of the seasons were already known to the Babylonians, but Hipparchus improved the values significantly. He created the foundation for accurate position measurements that followed the presentation of the position of the sun. The system introduced by Hipparchus and then generally accepted position measuring device, the armillary sphere, was calibrated by the sun.
Hipparchus also compiled the first known trigonometric table with tendons that formed the basis for trigonometric calculations. In modern notation, this is
The chord ( A) = 2 · sin ( A / 2),
He stated in steps of 7.5 °.