Abu Rayhan Biruni.

Abu Arrayhan Muhammad ibn Ahmad al-Biruni (973-1048) is a Central Asian scientist- encyclopedist. He was born in the suburb of Khwarazm city, the capital of the ancient state of Khoresm (nowadays a part of Uzbekistan).

Biruni has left us works devoted to medicine, geography, physics, astronomy, and at the same time has written science book about the stars, this book is in a matter of fact the textbook of an astrology for beginners.

Biruni’s science works cover the various fields of knowledge: astronomy and geography, mathematics and physics, geology and mineralogy, chemistry and botany, history and ethnography, philosophy and philology. The basic works (more then 40) are devoted to mathematics and astronomy which had huge practical value for an economic life of Khoresm - for the irrigation in agriculture and business travel.

The major discovery in astronomy was the creation of the calendar and the methods of orientation on the Earth by the stars in the sky. It was necessary to define the precise positions of the Sun, Moon, and stars in the sky and also to measure with the greatest possible accuracy the basic astronomical constants - an inclination ecliptic to equator (A great circle inscribed on a terrestrial globe inclined at an approximate angle of 23°27 to the equator and representing the apparent motion of the sun in relation to the earth during a year), and the length of the solar and stars year, etc.

Biruni has accepted and developed the progressive ideas of the ancient Greeks and the old Indian philosophers on some general subjects in astronomy: approved the identical fiery nature of the Sun and stars, unlike dark bodies - planets; the stars’ movement and their huge sizes in comparison with the Earth; the idea of gravitation. Biruni has stated some doubts about the validity of the geocentric systems of Ptolemy’s world.

In the very first composition “Chronology of ancient people " (1000) Biruni has collected and described all the systems of calendars from the various nations of the world known in that time. Astronomical researches are stated by him in the book of interpretation of the basic beginnings of astronomy and in other science works.