A Perihelion Sunday

 Today the Earth reaches the point in its orbit where it is closest to the Sun. This often seems ironic to some northern hemisphere dwellers, since for them it is also the coldest time of the year. In fact we are 3.3 percent closer to the Sun then when the Earth is farthest from the Sun in July. This point in the Earth's orbit is called perihelion and our planet is 91.4 million miles from the Sun. It may seem even more ironic to northern hemisphere residents that the Sun's disk actually appears 7 percent brighter than in the Summer. In freezing temperature weather, it is a small consolation to a Sun that remains low in the sky for so fewer hours than summer! All of this change in distance from the Sun results from the fact that the Earth's orbit is not a circle, but an ellipse. We have known this since 1606, from a man named Johannes Kepler

 Johannes Kepler proved mathematically that all the planets moved in elliptical orbits. This was no small feat in itself, and it was not immediately accepted by all. During this time, astronomy was in a transitional phase, and it was not a smooth one. For a very long time, for nearly two thousand years, certain beliefs had been held about the workings of the universe. It began about 355 BC, when Aristotle taught that the Earth sat, imperfect and changing, in the center of the universe. All the planets, the Moon, Sun and stars, moved in perfect spheres around the Earth. Aristotle's beliefs were reinforced in 140 AD by a Greek mathematician called Ptolemy. Ptolemy developed a model of the universe based on the teachings of Aristotle, again, the planets moved in uniform circular motion around the Earth. These views, this model, were to be held and supported by the church, then the leading authority.

 There were many problems with this model of the universe. It in no way accurately described the motions of the planets. However, the Catholic church had adopted Ptolemy's model as part of church dogma. It fit so perfectly into their vision of heaven and hell, with the heavens being perfect and unchanging and the least perfect place being the Earth. In 1543, the year of his death, the astronomer Nicolaus Copernicus published a book challenging that the Sun, and not the Earth, was the center of the universe. Fearing the wrath of the church, he refused to have the book published until he was dying. The Earth and other planets, he claimed, moved around the Sun. This part was, of course, correct, however, he still had the planets moving in perfect circular orbits. Sadly, the book got little attention. .One of Copernicus'  believers was Johannes Kepler, who worked under the great observational astronomer, Tycho Brahe.

 If ever there was a character, it was Tycho. He overate, he drank too much, he partied often, but he was one of the best astronomers there was. So accurate was Tycho's data, that it was used even in this century. One of the most unusual things about Tycho was that he had a good portion of his nose cut off while dueling with swords (drunken, of course) in a graveyard. The duel was over who was the better mathematician!  Compared to Tycho, Kepler was a wimp.

 Kepler was, unlike most of the astronomers in his time, born into a poor family. His mother was nasty, his father shiftless and seldom home. He was never healthy and became somewhat obsessed with his health in later years, nearly to the point of being a hypochondriac. Kepler did manage to work his way through the universities during which he became a believer in the Copernican theory of a Sun centered universe.

 In 1600, Kepler caught the attention of Tycho, who invited him to Prague. Kepler was thrilled to work for Tycho for several reasons. Tycho was famous for his accurate observational data, and Kepler wanted away from the area of Germany he was living in. Kepler was a protestant, and there was a great deal of persecution against Protestants during this time. Kepler's own mother was accused of witchcraft by the Catholic church and though Kepler was able to successfully defend her in a trial that lasted 3 years, she died the year after. Kepler had no reason to stay in Germany. Tycho represented a way to both escape and to work with good data.

Tycho was only interested in Kepler's mathematical abilities, not in sharing data. He set Kepler to work on the orbit of Mars. Tycho had a number of assistant working for him, but he was careful that they never got all the data. Tycho had no intention of painting the entire picture for lowly assistants and sharing  glory with anyone! It frustrated Kepler, who was trying to solve the mystery of planetary orbits.

 Kepler knew that uniform circular motion would not explain the motions of the heavens. He adopted the Sun centered model of Copernicus, and then added elliptical instead of circular orbits. All he needed now was to get the rest of the data on the other planets and see if it all fitted together. Unfortunately, it did not fit in with Tycho's plans, who refused to give up data to Kepler.

 As fate would have it, Tycho's greed would be his own undoing. In November of 1601, Tycho was invited to a nobleman's house to dine. In short, Tycho ate until he collapsed, and died 9 days later. Though on his deathbed Tycho asked the Holy Roman Emperor Rudolph II that Kepler be named royal mathematician in his place, Kepler was taking no chances. One night, shortly after Tycho's death, Kepler simply stole all the data! For Kepler, it was an incredibly brave deed, but it did enable him to publish a book about the elliptical orbits and Sun centered universe.

 It is Kepler's laws of planetary motion that allow astronomers to plot orbits and send spacecraft out into the solar system. We know when the planets rise and set because of Johannes Kepler's brillance.