In the classical scheme the Sun is one of the seven planetai, the wandering stars, and is called a luminary rather than a planet proper, sharing that rank with the Moon. It rules Leo as its sole domicile and takes its exaltation in Aries, with the fall in Libra and detriment in Aquarius. Ptolemy gives it the nature of hot and dry, and it is the chief of the diurnal or day sect, the sect division being one of the strongest interpretive tools in Hellenistic practice: a planet of the same sect as the chart is judged more favourably than the same planet in a chart of the other sect. Its natural significations are the father in a day chart, the ruler or sovereign, authority, the eyes, the heart, gold, and the vital principle by which a thing is what it is. Its apparent motion through the twelve signs is what defines the tropical zodiac in the first place.
Ptolemy's Tetrabiblos gives an exact reason for each planet's elemental quality rather than simply asserting it, and for the Sun the text states that its heat is heating and, to a certain degree, drying, a formula built from the same four-quality physics, hot, cold, wet, dry, that runs through the whole of ancient medicine and natural philosophy, not a claim peculiar to astrology. The Sun's place among the seven planetai reaches the Hellenistic synthesis, dated to roughly the first century BCE through the second century CE in Greco-Roman Egypt, from a much older layer of Babylonian celestial omen-reading and horoscopy stretching back to perhaps 1000 BCE, in which the Sun's behaviour, eclipses above all, was read for the fate of kings and states centuries before the Greek apparatus of houses, aspects and personal nativities gave it the individual, chart-based meaning it carries today.