Ancient history

The first of the great astronomers of whom we have knowledge is Hipparchus, who was born in Nicaea in the second century bc. Perhaps his greatest achievement was his catalogue of the positions and brightnesses of 850 stars in the northern sky. The catalogue was completed in 127 bc and represented a quite monumental achievement. A measure of his skill as an astronomer is that he compared his positions with those of Timocharis made in Alexandria 150 years earlier and discovered the precession of the equinoxes, the very slow change in direction of the Earth's axis of rotation relative to the frame of reference of the fixed stars. We now know that this precession is caused by tidal torques due to the Sun and Moon acting upon the slightly non-spherical Earth. At that time, however, the Earth was assumed to be stationary and so the precession of the equinoxes had to be attributed to a movement of the ‘sphere of fixed stars’.

The most famous of the ancient astronomical texts is the Almagest of Claudius Ptolomeaus, or Ptolemy, who lived in the second century ad. The word ‘Almagest’ is a corruption of the Arabic translation of the title of his book, the Megelé Syntaxis or Great Composition, which in Arabic becomes al-majisti. It consisted of 13 volumes and provided a synthesis of all the achievements of the Greek astronomers and, in particular, leant heavily upon the work of Hipparchus.