Kepler Compendium

Today on Fizzix Phriday, it's time for some physics phistory (the p is silent). Let's take a jaunt back in time to the year 1571. Nicolaus Copernicus (born Mikolaj Kopernik) had published his revolutionary work, De revolutionibus orbium coelestium (in English: On the Revolutions of the Celestial Spheres) just 23 years ago, where he described, mathematically, a universe where the Earth was not the center, and all the planets revolved around the Sun, rather than the Earth. While this was a revolutionary idea, it was largely seen as incorrect or ignored, due in no small part to Copernicus's death around the time of its publication, and being therefore unable to defend his work from criticisms that arose from going against the established ideas in science and religion. Even worse, a note was prepended to his work before publication that basically said "everything in here about the Earth revolving around the sun and not the other way around is just a neat mathematical exercise, not the truth of things." This was likely added by the person he sent the manuscript off with to be published as an attempt to protect Copernicus, as the Pope had declared any view other than the geocentric (Earth-centered) one to be heretical. However, it did no good to protect him (as he died before his manuscript's widespread distribution), and it prevented the ideas within from being taken too seriously.

However, in this year, a man named Johannes Kepler was born. Fascinated by astronomy from an early age, he spent his years in seminary also studying the works of Copernicus, and coming to the conclusion that they were likely correct. In 1595, he published Mysterium Cosmographicum (in English: The Cosmographic Mystery), in which he defended the heliocentric (sun-centered) point of view. This was not, however, widely distributed or read, in part because Kepler was not a well-known astronomer, and had no foothold in high society, as he was born into a poor family. However, he was to encounter a stroke of luck.

Tycho Brahe was a noble-born astronomer, and probably the best when it came to observational astronomy. As telescopes had yet to be invented, everything had to be seen via the naked eye, and Tycho had one of the best. He was also a bit of a character, as he once was involved in a duel, allegedly over mathematics, where he lost his nose. He wore a metallic one which was made to look approximately flesh-toned and was glued weakly to his face. His lavish observatories were both scientifically wonderful and a hedonist's dream, if tales are to be believed. It was in 1600 that Kepler first met Tycho Brahe, and in 1601 he was brought on to work as his assistant. Tycho, however, did not have any intentions of keeping such a low-born man around for two long, only a few years at most. What was fortunate for Kepler was what happened on October 24th, 1601.

In October, Tycho was at dinner with a Baron and drank too much (which was not uncommon for him). However, he refused to excuse himself before the Baron left the table, and, as a consequence, developed a urinary issue which developed into an infection that finally killed him on October 24th. Reportedly, he uttered the phrase "May I not have lived in vain" multiple times on his deathbed. He didn't live in vain, as Kepler now was able to seize all of Tycho's detailed observations of the planets and use them to propel astronomy forward.

Ultimately, eight years later, in 1609, Kepler published Astronomia Nova seu physica coelestis, tradita commentariis de motibus stellae Martis ex observationibus G.V. Tychonis Brahe, or Astronomia Nova for short (in English: The New Astronomy). This book is regarded as one of the greatest and most influential astronomical books ever. In it, with no ifs, ands, or buts, he explicitly refuted the geocentric view of the universe in favor of a heliocentric universe, and gave both the math to prove it and the observational data that fit the math. In this volume, he explained the first two law of planetary motion, which form the basis of all modern astronomy and physics:

  • Each planet moves in an elliptical orbit with the sun at one focus. The orbit of each planet, including the Earth, is around the sun. These orbits are not perfect circles, as everyone wanted them to be (because circles were "perfect," and the universe should abide by "perfect" principles), but are ellipses. The sun is at one of the focii of the ellipse.
  • Each planet sweeps out equal areas in equal time. During its orbit, a planet will move faster when closer to the sun and slower when further away. The area of a "slice" of the ellipse, with the point of the slice being the sun and the edges being a part of the planet's orbit is what governs how much time the planet takes to traverse that outer edge of the slice. The distance of the outer edge (or the path of the orbit) doesn't matter, only the overall area of the slice of the ellipse created by the orbit.

Oh, boy, was that stuff important. Those laws are Earth-changing. And, what was best about it, is that he had Tycho's data to back him up. Now, of course, we tend to take for granted what Kepler had worked out. But keep in mind, before this, every main theory of the heavens involved planets moving in circles. Circles were the thing. They were where it was at. Kepler sat down, looked at the data, did the math, and said "No, that's not right. You can't make it work with circles. But here's how it does work. Also the Earth isn't the center of the universe."

This should have been Earth-shattering. Kepler was right about all of this. But the fact that Astronomia Nova went against every bit of established doctrine at the time means that it garnered little attention. He received praise for his mathematics and the ability of his equations to accurately predict the planetary motions, but was told, essentially "you need to figure out how to make it work with circles." The astronomical and religious community simply couldn't deal with the universe not being perfect, according to their preconceived notion of perfection. Even when Galileo, a rather popular scientist, affirmed Kepler's work later after the invention of the telescope, it still wasn't widely accepted (and Galileo was put under house arrest by the Pope). It wasn't really until Newton laid down the Law (that Law being the Law of gravity) that people finally accepted the Keplerian principles.

Because no one really wanted to discuss his most important work, Kepler explored other avenues of math and science. After the telescope was invented, he showed how to make a better, multi-lens version due to his heavy study of optics. He proposed the idea of a magnetism-like force that would keep the planets in their orbit, which was later affirmed beyond all doubt by Newton (man, Newton was a machine. I'll talk about him at some point). He wrote a treatise on the hexagonal symmetry of snowflakes, proposing what may be the cause of them. He also came up with what has come to be known as the Kepler Conjecture, which describes the most efficient manner of packing spheres in an enclosed space. It was not until 1998 that this conjecture was "proven" (in this case, with only 99% certainty, as it was a proof by exhaustion) by Thomas Hales.

In short, Kepler was one of the most influential astronomers in history, giving us the first correct and complete model of a heliocentric universe. His work influenced countless others, and today NASA has named a space observatory after him, which currently is sitting in space finding exoplanets. Though he may not have been seen as such in life, he was definitely the greatest astronomer of his time. He literally wrote the book on planetary orbits, and it's stuff we still learn in physics today, over 400 years later.

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