Parenti’s recent article, Finding the Cosmic Order: The Story of Kepler’s Laws of Motion, appeared in the society’s September newsletter. Kepler was a pivotal figure in the scientific revolution of the 17th century. He’s well known for his laws of planetary motion, which were a foundation for Isaac Newton’s groundbreaking theory of universal gravitation.
The Westchester Academy middle school student, a youthful astronomer himself, states in his article that “we might not have the same understanding of the universe that we do now” without breakthrough scientists like Kepler and Newton.
NASA’s busy Kepler spacecraft is the “in the news” science and astronomy object that the young writer uses to take readers on a journey into Kepler’s discoveries in the fields of science and astronomy.
View the full September issue of the “Guidestar” newsletter:
Clay Parent’s newsletter article can be read here:Page 12, September 2015
Finding the Cosmic Order
By Clay Parenti
The Story of Kepler’s Laws of Motion
NASA’s Kepler spacecraft has made lots of news recently, helping astronomers discover many exoplanets orbiting other stars, such as super-Earth Kepler 452b, which was just found recently. But who was Kepler?
Johannes Kepler’s laws of motion marked a major turning point in the history of astronomy and science. It threw out the old systems of epicycles and orbs and replaced it with a system based on physics and observation that holds true to this day. Kepler’s book on his discoveries, Astronomia Nova, or “New Astronomy” was well named. It was the beginning of a scientific revolution in astronomy that led to Newton and the rest of modern science, astronomy and physics. Without them, we might not have the same understanding of the universe that we do now.
The story of Kepler’s laws of motion begins with Johannes Kepler, a former seminary student and at that times a teacher in Austria. While he was teaching, he had an epiphany. He wondered why there were only six planets and five platonic solids (These solids look like the many sided dice used in the game Dungeons and Dragons). Could they be connected? Could the platonic solids have something to say about the distances between the planets? He named his theory (which was that the spacing of the platonic solids predicted the spacing of the planets) the Mysterium Cosmographicum or “The Cosmic Mystery” and set out to find evidence to prove his theory. His theory somewhat agreed with the rudimentary astronomical observations of the time and disagreed with others. He badly needed good observations. At that time, the best astronomical observations at that time were in the hands of an observational genius named Tycho Brahae, the Imperial Mathematician for the Holy Roman Empire.
Tycho Brahae was a Danish nobleman and astronomer who were renowned for his exceptionally accurate naked eye observations of the night sky. A colorful figure, he had lost his nose in a duel over a mathematical formula and wore an artificial nose. Tycho believed the planets orbited the Sun, which in turn orbited the Earth. Kepler visited Tycho at his observatory in Prague and considered working for him to see if his data confirmed his Mysterium Cosmographicum. After he returned home, Catholics invaded Austria, and Kepler was banished after he refused to convert to Catholicism. He went to Prague and began to work for Tycho.
Tycho, not wanting to be eclipsed by a potential rival, was reluctant to give all of his observations up to Kepler. Instead, he only gave him little bits at a time. With so little data, it was hard for Kepler to progress on his Mysterium Cosmographicum and the projects that Tycho gave him to work on. They constantly fought and quarreled. Then Tycho suddenly died of uremia. His dying words were “Let me not seem to have lived in vain.” Kepler inherited Tycho’s observations and his position as Imperial Mathematician. Now, with Tycho’s observations, he could finally prove his Mysterium Cosmographicum.
After looking at Tycho’s data on Mars, Kepler found that the Mysterium Cosmographicum was wrong. He then tried to explain the movements of the planets, but circular motion didn’t conform with observations. Then he tried motion in an ovoid, but that too failed to conform to observation. Desperately, he tried motion in an ellipse. It fit in perfectly with the data. Using this discovery, he formulated his first law of planetary motion: A planet travels in an ellipse with the Sun at one focus. Next, he found his second law of planetary motion when he compared the motions of planets when in different parts of the sky relative to the Sun. He found that a line joining the planet and Sun sweeps out equal areas in equal times, so that planets move faster when they are closer to the Sun and slower when they are further away. Kepler suggested a force akin to magnetism could be responsible for these motions.
These laws of motion were among the first non-mystical explanations of the movements of the heavenly bodies. Kepler’s laws are obeyed by all bodies in the universe, and have stood up scrutiny for centuries. They were the beginning of a new way of thinking of the universe that the Kepler spacecraft is helping us explore.