On combinatorial arithmetic in antiquity, see A. The radius of the circle is then 360. It consisted of no less than 850 stars, with all their positions and movements accounted for. Hipparchus active 2nd century bc Greek astronomer. In devising a model to account for the inequity of solar motion, Hipparchus was more successful than with the planets and the moon.
Hipparchus holds the distinction of developing trigonometry. Hipparchus is the first Greek known to have used this material. Hipparchus was also the first person to bring to Greece the idea of dividing a circle into 360 degrees. With respect to the moon and sun, Hipparchus was indebted to the Babylonians, but he improved upon earlier estimates of the size and distance of the two bodies. Born at Nicaea in Bithynia, Hipparchus studied astronomy, perhaps under Theodosius, and made some of his early observations in his native city. Like many another, his greatest achievement was to make it possible for his successors to eclipse him and relegate his works to oblivion.
Hipparchus was able to prove that the direction of this rotation changed slowly in time. Gundel, Neue astrologische Texte des Hermes Trismegistos Munich. Since Hipparchus did treat these subjects, the question arises whether he used spherical trigonometry. Let us first summarise the main contribution of Hipparchus and then examine them in more detail. Furthermore, for one of the observations Ptolemy says Hipparchus used instruments plural. Because of these accordances Delambre, P.
© 2017 All Rights Reserved. Notably that for his observation of 2 May 127 B. Ptolemy cites more than 20 observations made there by Hipparchus on specific dates from 147 to 127, as well as three earlier observations from 162 to 158 that may be attributed to him. Hipparchus criticized severely the geographical work of Eratosthenes c. We believe that Hipparchus's star catalogue contained about 850 stars, probably not listed in a systematic coordinate system but using various different ways to designate the position of a star. He was eventually able to come up with a means of predicting solar eclipses thanks in large part to his knowledge about astronomy and his innovative discoveries in trigonometry. This last point shows that in any detailed discussion of the achievements of Hipparchus we have to delve more deeply than just assuming that everything in the 's Almagest which he does not claim as his own must be due to Hipparchus.
About he made the first astrolabion, which may have been an or the predecessor of a planar instrument , which was improved in 3rd century by Arab astronomers and brought by them in in. He also applied his methods to the solution of the problem of determining planetary positions. Hipparchus found 71 as the least distance. In discussing lunar latitude, he used data from the eclipse of 502, derived from cuneiform sources; he determined the inclination of the lunar orbit to the ecliptic to be 5 °. At the end of book 3 is a list of bright stars that lie on or near twenty-four-hour circles, beginning with the hour circle through the summer solstice.
If this was so, we can explain more easily how Ptolemy was able to select eclipses with very special circumstances to suit a particular demonstration : he was using material already digested by Hipparchus. The true value is about 60 times. Whether Hipparchus gave such coordinates for every star in the catalog or only for some selected stars remains uncertain. This table provided an effective method to solve trigonometric problems. This model of the Sun's motion described the actual motion of the Sun fairly well. By means of his trigonometric calculations he was able to determine, with greater accuracy than ever before, right and oblique ascensions and declinations, as well as simultaneous risings or settings of stars at different terrestrial latitudes.
This gives his rate of precession of 1° per century. Since when refers to results of Hipparchus he does so often in an obscure way, at least he seems to assume that the reader will have access to the original writings by Hipparchus, and it is certainly surprising that neither or fills in the details. Third, there was commentary on Aratus by Attalus of Rhodes, written shortly before the time of Hipparchus. Our knowledge of the work is derived almost entirely from Strabo. There are records of observations he made in his native Bithynia as well as from the island of Rhodes and the Egyptian city of Alexandria. Hipparchus' discussion of the motion of thepoints of solstice and equinox slowly from east to west against thebackground of the fixed stars is perhaps his most famous achievement; he hasbeen therefore credited with the discovery of the precession of theequinoxes.
Hipparchus holds the distinction of developing trigonometry. The reason for this change is an almost imperceptible wobble on the axis of the earth which causes the sun to move backwards as a pointer against the constellations, gradually tracking backwards one degree every 72 years or so. Our planet wobbles like a top as it spins, and over time, this means that the poles of our planet slowly shift the direction in which they point in space. The observer looked through a hole in a block at one end of the rod, and moved a prism that slid in a groove along the top of the rod until the prism exactly covered the object sighted. Sizes, Distances, and Parallax of the Sun and Moon. Dreyer, A History of Astronomy from Thales to Kepler rev. His star map was thoroughly modificated as late as 1000 years later in by A.
He was the first person to record the actual angular positions using the ecliptic as a base line. This gap between theory and observation, though, was not significant among Greeks until conquered the East and Greek geometrical astronomy began to merge with the observational-based Babylonian astronomy. Importance to Astronomy Hipparchus is often called the first real astronomer, as he was the first Greek to actually make systematic observations of the sky. In attempting to construct a lunar theory Hipparchus was faced with much greater difficulties. However, it was a rigid model that could not account for certain observations such as the changes in the brightness of the planets, their retrograde motions, and changes in their speeds: these observations clearly contradicted the Aristotelian model. The references to Hipparchus by name can be found from the index in Manitius or that in J. There is independent evidence that he used this value, and that it is of Babylonian origin.