An image of a 'zodiac man', showing the parts of the body governed by the various signs of the zodiac.
Image by kind permission of the Master and Fellows of Trinity College, Cambridge.
Astrology - belief in the physical influence of planetary rays on earth - is one of the most important historical contexts in which astronomy developed.
Astrology served as a motivation as well as a means of gainful employment for astronomers.
The Babylonians meticulously compiled tablets of the position of Venus, as it was believed to signify omens for weather, war, famine, diseases, rulers and kingdoms.
Ptolemy composed the Tetrabiblos, believing that astrology could be placed on a rational footing, despite being a conjectural art like medicine.
In practice, belief in astrology meant that horoscopes were cast for new-born children, prospective spouses and political enemies, public buildings were opened and marriage and other ceremonies conducted on auspicious days. Numerous records of astrological practice can be found from the Roman times.
Several important Arabic authors on astronomy, such as al-Kindi, Masha'allah and Abu Ma 'Shar were astrologers: Abraham ibn Ezra and Ibn Yunus discussed astrology in a scholarly manner.
In the Latin West, the terms astrology and astronomy were interchangeable for a long time.
In the arts faculties of medieval universities, the theory of planetary motion of Sacrobosco, Ptolemy and Gerard
of Cremona (later Georg Peurbach) was always taught alongside guides for interpreting the influence of planetary configurations, through texts such as Alchabitius' Introduction to Astrology, Ptolemy's Tetrabiblos and Centiloquium and Albumazar's Great Conjunctions.
Johannes Kepler believed that he could set astrology onto a surer footing, and his astrological beliefs were fundamental to his heliocentric cosmology.
