it is important to distinquish the difference between astrology and astronomy. The most basic is that nowadays astrology is no longer science field.
Today I want to talk about astrology when it was mainstream. For this to be true we have to move back few years, I want talk about renessaince, so that is about 400 years.
These days astronomy has gained a great improvement since old times. This improvement is mostly in two things: heliocentric model and first telescope.
There were couple of important people who all worked on this heliocentrism, it whole started with Copernicus, followed by Tycho Brahe, Johannes Kepler and Galileo Galilei. Now I want talk about Tycho and Johannes because both of them were astrologers too.
Tycho Brahe is known as one of the most or simply most precise observer. It is said that he was able to make measurements 10 times more accurate then most other people (means measurement of 1/4 of arcminute). He probably has the least credit for heliocentrims of those four guys because at one point he rejected the idea and rather made his own geo-helio centric model.
Anyway he was working on the court of Rudolf II. The Holy Roman Emperor. Not only that he was making very good measurements but he also created zodiac for the king.
While there are tons and tons of zodiacs, usually it is about the position of celestial objects. Imagine clock laid on the ecliptic. Then switch all the numbers for the signs in zodiac. Then when planet passes in the angle which is for the zodiac you say that for example: “Mars is in the sign of Pisces”. Those are also actuall constellations on sky.
Johannes Kepler is known for his laws of planetary motion. He did not have very good eyesight so when he met with Tycho Brahe he just helped him with math and also with processing all the data that he measured, though Tycho guarded them carefully.
Kepler was also interested in astrology, actually he probably spent the same amount of time on astronomy as on astrology. He worked with Tycho also on the court of Rudolf II. who was very willing to finance their exploration.
It took some more years for people to realise that as astrology also alchemy is not a science and is not worth of time.
Also check out this cool blog about math!