Alchemy, astrology and Magic always seem to go together. They were combined in the early renaissance as a deliberate act, but early on they were informally combined as they all fit the same cosmology and religion.

We have seen a hint of this in Plato, where he had the Gods living far outside the sphere of the earth, and by the rotation of the planetary spheres have some influence over the earth. Aristotle made this a central aspect of his cosmology. But the origins are earlier.

From Persian Zoroastrianism (600 B.C., note the date relative to the conquest of the old world by the Persians) came the love of wisdom and the idea that all the world seeks to be like God. As these ideas were carried to Greece by Heraclitus (500 B.C.) he brought with it some mathematics which inspired Pythagoras, the eastern forms of astrology, and the practice of natural magic brought to Greece by Ostanes.

Astrology was practiced by everybody by about 2000 B.C. The astrologers controlled the calendar, and most religions incorporated astrology as the means of finding out which gods were influencing you right now. Egyptian religion went as far as to enumerate the "siderial gods" 36 in number, who rule each 40-minute block of each day.

Magic was not the black magic we play with on Halloween, it was the natural magic of using herbs to heal. It was a forerunner of medicinal alchemy and medicine. It required a vast understanding of the plants and how to prepare them so they would heal.

As these arts were practiced, the astrologer would calculate which planets were in the sky at your birth. Since you came from heaven, your soul needed to pass through each planetary sphere, picking up the vice associated with each one (pride, envy, wrath, sloth, greed, gluttony, lust) each associated with a particular body in the cosmos. As these influence us, some have greater influences than others. That imparts our character. 

These vice-like aspects can be overcome. It requires that the astrologer find the "antidote" by finding the planets, stars, plants, shapes, objects that will undo our vices, then at the correct time of year, at the feet of the correct statue of deity, imbue a talisman that can help undo our vices. Potion making worked the same way. 

An astrologer would need to be a magician and later an alchemist to perform astrology. Alchemists relied on astrologers to get the timing right, and later some would become makers of medicines.