Aristarch is Copernic of Classic World.

Aristarch (near 310 - 250 years - III c. B.C.) was born in Samos island. Aristarch's teacher belonged to Aristotel school.

Aristarch tried to determine the distance to the sky solids with the help of observation. First Aristarch determined the fact for how many times the Sun was father then the Moon and then he compared the Sun and the Moon with the Earth. He proved that the Moon was smaller than the Earth in three times and the Sun was in six times more than the Earth. What was the most important that Aristarch's work was not the result but the fact of realization showed that it is possible to cognize the world of celestial solids.

Aristarch came to the conclusion that the great Sun could not revolve around the small Earth. Only the Moon rotates around the Earth. The Sun is the centre of Universe. All planets turn around the Sun. This theory is called heliocentric.

Aristarch contemporaries rejected heliocentrizm. The change of epochs would be required in order heliocentrizm came into people awareness.

Gipparch.

Gipparch was born in Nikeja town in small Asia. The main part of his life he spent on the Rodos island in Aegean Sea. There he built an observatory. Gippagch systematically observed the celestial solids. He was the first who introduced the geographical coordinates network of meridians and parallels which helped to determine the latitude and longitude on the Earth as well as the astronomers determined the stars coordinates (slope and ascent) on the imaginary sky sphere.

Gipparch suggested that the Sun turned around the Earth steady and in circumference but the Earth is displaced according its centre. Gipparch called such an orbit eccentric and the value of the centres displacement (according to the radius) - eccentricity. He discovered that for explaining of different year duration (spring duration - 94,5 days, summer - 92,5 days, autumn - 88 days, winter - 90 days), the eccentricity 1/24 should be taken. The orbit point in which the Sun is nearer to the Earth Gipparch called perigee and the most remote one he called apogee. The line connected the perigee and apogee was called apsid (from Greek "apsidos" - "vault", "arch").

Gipparch compose a star catalogue where the coordinates of 850 stars were registrated according ecliptic (the line of a year Sun movement). Comparing his results with the coordinates of some stars measured by Aristotel and Timokcharis (the contemporaries of Aristarch Samossky) Gipparch discovered that ecliptic longitudes increased equally and latitudes were not changed. He came to the conclusion that the sky equator was slowly displacing. Gipparch discovered that the lunar orbit is crossed with the ecliptic plane in the two points junction and eclipses might occur if the Moon was in these points of its orbit.

1, 2 - the angular tools, which Gipparch used to measure the sky coordinates. Transverse beam on the astronomic staff (1) was set in such a way that rays from two celestial bodies coming through sighting holes on the beam get to the sighting hole on the staff and to the observer eye. The vertical circle (2) was used to measure the hight of the celestial body above the horizon. 3 - geometrical scheme of the Moon eclipse, which Gipparch used for valuing the distance the Earth - the Sun and the Earth - the Moon. He measured the angular dimensions of the Sun 2a and the Earth shadow 2b. Using the geometrical scheme Gipparch discovered that the distance to the Moon is about 60 terrestrial radiuses.

Gipparch was the first who used the ancient babylon astronomers achievements. This allowed him to determine a year duration. Gipparch could forecast the moon eclipses within an hour accuracy.

Gipparch found that planets' movements are very complicated and could not be described by simple geometrical models. But at that time it was impossible to find the way out. Only three ages later "the celestial legacy" of the great astronomer was taken by Ptolemei who could build the world scheme according to the observations.