Al-Bitruji: He pointed out many errors in Ptolemy’s hypothesis of
solar system and in 1150 proposed a new system for the planetary
motion.
Ibn al-Alam: Determined the stellar motion by observing that the
stars traverse one degree in 70 solar years. He also determined the
latitude and longitude of many stars and measured the greatest
declination of the planet Mercury, he discovered the moons
(satellites) of Jupiter, discussed the motion of sunspots and
determined the eccentric orbits of the comets.
Ibn-ul-Hassan:Discovered that the moon’s distance from the sun is
not constant as measured by Ptolemy.
Umar Khayyam: He was the court astronomer of Malik Shah
Saljuq. He reformed the old Persian calendar, in such a way that the
solar calendar proposed by him is more accurate than any calendar
proposed either before of after his time.
