Greatest astronomer of his time. Al-Battani determined more accurate and improved time-tables of the position of the sun and the moon. His remarkably accurate calculation of the solar year as 365 days, 5 hours, and 46 minutes and 24 seconds is very close to the latest estimate. Al-Battani revised orbits of the Moon and the planets and proposed a new and very ingenious theory to determine the conditions of visibility of the new moon. Dunthorne, in 1749, used al-Battani's excellent observations of the lunar eclipses to determine the acceleration of motion of the moon. Al-Battani's fame came also in Mathematics with the use of trigonometric ratios as we use them today. He was the first to replace the use of Greek chords by Sines, with a clear understanding of their superiority. He also developed the concept of Cotangent and furnished their tables in degrees. Al-Battani wrote many books on astronomy and trigonometry. His most famous book was an astronomical treatise with tables, which was translated into Latin in the 12th century and printed at Nuremberg in 1537 and 1645 and is known by the title: 'De Scienta Stellarum - De Numeris Stellarum et motibus.' His another book 'al-Zij' was published by C A Nulino in Rome in 1899. Copernicus in his book 'De Revolutionibus Orbium Clestium' expresses his indebtedness to Al-Battani. Al-Battani, known in the west as Albategnius, whose full name was Abu Abdullah Muhammad Ibn Jabir Ibn Sinan al- Battani, was born in or near Battan, in state of Harran, Turkey. He was the son of a well-known scientist. At the end of the ninth century he migrated to Samara, where he worked until his death.