Today’s dive into my GCSE book on Astronomy, lead me into the life of Johannes Kepler (1571-1630). He was assistant to Tycho Brahe, studied previously. Tycho “could not accept the heretical idea that the Earth moves round the Sun, and preferred a weird hybrid system according to which the planets moved round the Sun while the Sun itself was in orbit around the Earth.”
Kepler, however, “soon found that the movements of Mars, in particular, could not be explained” in this way. For ten years he studied the movements of Mars.
Those that know the planets as we understand them know that Mercury and Venus orbit closest to the Sun, then there is the Earth, and further out is Mars; the closer the planet lies to the Sun, the quicker it orbits (Mercury takes just three Earth months, whereas Mars takes almost two Earth years). [link]
Having astronomical software freely to hand, rather than having to hope for clear skies and freeze one’s socks off outside (as it is rather chilly out now), means we have it easy, the laborious work done for us in plotting the positions of the planets.
A year’s observations producing this illustration in Stellarium (with the added luxury of being able to remove the ground):
Mercury is in yellow and Venus is white, and their orbits we can see in their entity, squiggling about (again, this is as viewed from here on Earth). The orbit of Mars, in red, is incomplete because it takes longer than a year, so we can appreciate why it took Kepler ten year’s worth of observations to properly realise and explain what was going on. Below is what then years of Mars orbits would look likes (this time in yellow):
Pretty stuff. It was in late 1604 that Kepler at last hit upon the idea that the orbit of Mars was that of an ellipse, rather than the perfect circle. He had previously assumed an ellipse to be too simple a solution for earlier astronomers to have overlooked. “Finding that an elliptical orbit fit the Mars data, Kepler immediately concluded that all planets move in ellipses, with the Sun at one focus*…” Here is an illustration from his work:
It appears to me quite telling that the diagram is formed within the twelve signs of the zodiac, rather than say something more specific, calculated and mathematical like degrees. (It’s a shame I’m not adept enough with Stellarium to produce something akin to this.) Kepler studied the skies in a time when there was little difference between astronomy and astrology. Indeed, he was an advisor to (Holy Roman) Emperor Rhudolf II:
Kepler’s primary obligation as imperial mathematician was to provide astrological advice to the emperor. Though Kepler took a dim view of the attempts of contemporary astrologers to precisely predict the future or divine specific events, he had been casting well-received detailed horoscopes for friends, family, and patrons since his time as a student in Tübingen. In addition to horoscopes for allies and foreign leaders, the emperor sought Kepler’s advice in times of political trouble. Rudolf was actively interested in the work of many of his court scholars (including numerous alchemists) and kept up with Kepler’s work in physical astronomy as well. – Wikipedia
Here is such a horoscope/chart he produced, this one being for General Wallenstein:
Here’s some more on Rhudolf himself:
Astrology and alchemy were regarded as mainstream scientific fields in Renaissance Prague, and Rudolf was a firm devotee of both. His lifelong quest was to find the Philosopher’s Stone and Rudolf spared no expense in bringing Europe’s best alchemists to court, such as Edward Kelley and John Dee. Rudolf even performed his own experiments in a private alchemy laboratory. When Rudolf was a prince, Nostradamus prepared a horoscope which was dedicated to him as ‘Prince and King’. In the 1590s Sendivogius was active at Rudolph’s court.
Rudolf gave Prague a mystical reputation that persists in part to this day, with Alchemists’ Alley on the grounds of Prague Castle a popular visiting place and tourist attraction.
Here is where things get somewhat strange. Kepler is “best known for his laws of planetary motion, and his books Astronomia nova, Harmonices Mundi, and Epitome Astronomiae Copernicanae. These works also provided one of the foundations for Newton’s theory of universal gravitation.” So?
The Epitome Astronomiae Copernicanae was an astronomy book on the heliocentric system, the first volume of which just so happened to land itself on The Index Librorum Prohibitorum (“List of Prohibited Books”) in 1619. It was a list of publications deemed heretical or contrary to morality and Catholics were forbidden to read them without permission.
To me this looks like a case of royalty using occult systems whilst trying to ban such things among the general public. This may have been the 1600s but I wonder how much has changed since then.
Just prior to this prohibition, in 1617, Kepler’s own mother was accused of witchcraft and imprisoned for fourteen months, even though there was little to no evidence. This was at a time when witchcraft trials were relatively common in central Europe. It took an extensive legal defence drawn up by Kepler to see her released, not before being subjected to attempts to obtain a confession.
*Regarding the elliptical orbits of the planets
That an ellipse is drawn with the Sun at one focus makes me wonder what is at the other**! Curiously, while the orbits of the planets are elliptical, the depiction of this is often exaggerated to make the point, but the fact is, they’re only slightly elliptical (therefore, if there were something at this other focus, it would be close to the Sun). This makes me wonder how the discovery of the elliptical orbits of the planets came about and why that’s such a key point in the development of astronomical laws.
**Answer: “Due to the force of gravity, which goes as the inverse of the square, planets trace out an ellipse in space as they orbit around the sun, which is located at a single focus. The other focus is unphysical.” [link] No Nemesis Sun here.