Al-Kindi took his view of the solar system from Ptolemy, who placed the Earth at the centre of a series of concentric spheres, in which the known heavenly bodies (the Moon, Mercury, Venus, the Sun, Mars, Jupiter, and the stars) are embedded. In one of his treatises on the subject, he says that these bodies are rational entities, whose circular motion is in obedience to and worship of God. Their role, al-Kindi believes, is to act as instruments for divine providence. He furnishes empirical evidence as proof for this assertion; different seasons are marked by particular arrangements of the planets and stars (most notably the sun); the appearance and manner of people varies according to the arrangement of heavenly bodies situated above their homeland.
However, he is ambiguous when it comes to the actual process by which the heavenly bodies affect the material world. One theory he posits in his works is from Aristotle, who conceived that the movement of these bodies causes friction in the sub-lunar region, which stirs up the primary elements of earth, fire, air and water, and these combine to produce everything in the material world. An alternative view found in the treatise On Rays (De radiis) is that the planets exercise their influence in straight lines; but this treatise, written by a Latin author, probably around the middle of the 13th century, is apocryphal. In each of these, two fundamentally different views of physical interaction are presented; action by contact and action at a distance. This dichotomy is duplicated in his writings on optics.
Some of the notable astrological works by al-Kindi include:
*The Book of the Judgement of the Stars, including The Forty Chapters, on questions and elections.
*On the Stellar Rays (spurious)
*Several epistles on weather and meteorology, including De mutatione temporum, ("On the Changing of the Weather").
*Treatise on the Judgement of Eclipses.
*Treatise on the Dominion of the Arabs and its Duration (used to predict the end of Arab rule).
*The Choices of Days (on elections).
*On the Revolutions of the Years (on mundane astrology and natal revolutions).
*De Signis Astronomiae Applicitis as Mediciam On the Signs of Astronomy as applied to Medicine
*Treatise on the Spirituality of the Planets.