During the continuous scrutiny of the early models of the solar system, there was little explanation for the ethereal bodies that roamed the night sky. Gravity was not to be discovered until Newton gave Halley (the guy that discovered the comet) a helping hand in August 1684[5], and so a solution came about in the form of early mythology.

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Within the field of astrology, it was taught that the planets had great influence over the Earth, being able to affect both our moods and personalities. It was deduced that the higher a planet was in the sky at the time of our birth, the more affected we were by its pull. For example, those born under the rule of Saturn are susceptible to gloomy thoughts of apathy – bad news if you’re a Capricorn.
Under this train of thought, it was also possible to determine how an individual might react to certain, unspecified looming events. Furthermore, by following the paths of planets, one could also determine how that individual could best approach these situations; waiting to react until a certain, unhelpful planet had passed across the sky, or until a countervailing one had ascended.
 

This was all very well and good, and for a considerable amount of time not many people cared very much for the true nature of the planets or how they came to be. Not many, but Johannes Kepler was a man who definitely did.
A professor of Mathematics and an ardent astronomer, Kepler’s prime motivation was in trying to find a way to shield people from the sometimes inconvenient effects of the planets[6], but it was also his fervent belief in the Copernicus system which made him look to uncover the movement of the planets.
Sure, he was as religious as the next guy back then, and his belief that the sun was at the centre of the solar system had more to do with the linguistic implications of the term ‘Son of God’, than it having any grounds in actual science[7]. Nonetheless, it spurred him on to assess Tycho Brahe’s observational data of Mars[8], determining that its apparent backward trajectory was in fact a working of its own ellipses and Earth’s spinning axis[9]. These combined made it appear to move backwards across the sky at different times of the year. This planetary ellipse was thus seen to be an occurrence reflected across all of the planets, and so confirmed the heliocentric view that the Sun was indeed the central point around which all of the planets orbited.

In uncovering this elliptical information, Kepler went on to attribute the movements of the planets to three mathematical laws, all of which are still in use today:

1. All planets move in elliptical orbits, with the sun at one focus - that one’s pretty self-explanatory.

2. A line that connects a planet to the sun sweeps out equal areas in equal times - when it’s closer to the sun, it sweeps around faster, when it’s further away, it slows down.

3. The square of the period of any planet is proportional to the cube of the semimajor axis of its orbit. This law arises from Newton’s law of gravitation - don’t even expect me to explain this just yet, because I don’t think I can.[10]

And so it was that we understood the paths of the planets. Still, this didn’t explain why they perpetually circled the sun. And so let us refer back to that fateful summer of 1684, when a member of the Royal Society reached out to Isaac Newton for help understanding the ‘why’ behind Kepler’s three laws.

In truth, Mr. Newton was more into his alchemy than he was his astronomy, but after being hounded by Halley, Hooke and Wren, who needed help in calculating the precise force which determined a planets distance from the sun, he went on to not only successfully provide them with the correct calculations, but most prominently to ascertain that this force was Gravity[11].

From here, Halley went on to measure his comet’s movement around the sun, and many more astronomers and physicists made great contributions to our understanding of the Milky Way.

So it was that astrology began to fall out of favour as an explanation for the Natural World. Still, it was an important precursor to the understanding of the cosmos, and is still widely revered to this day.