Tycho Brahe had a love-hate relationship with his brash young assistant Johannes Kepler. Over the year and a half they worked together, Kepler and Brahe fought, Kepler left in angry fits or Brahe would order him to leave, then one or the other would beg to work together again. For some reason they needed each other. Brahe's observations of the universe were unsurpassed throughout the world. Kepler wanted access to them to devise better descriptions of how the heavens worked. Brahe, in turn, needed Kepler's brilliant math skills to help prove his own theories.
But they rubbed each other the wrong way, and Brahe wanted to keep him occupied and out of his hair. "Describe for me the orbit of Mars," he told Kepler in 1600, knowing full well that all the greats of history had wrestled with the prickly warrior planet and come up short.
"Give me a week," replied Kepler.
Kepler was overconfident. It would take him eight years to hammer out the orbit, but when he did, he turned Ptolemy's model on its head. He described the way the planets move with three laws that are still taught in introductory physics classes around the world.
Brahe and Kepler's names aren't well known outside the world of astronomy, but their contributions to science were as crucial as those of the more famous Copernicus and Galileo. In fact, some historians argue that the vision of a sun-centered cosmos that Copernicus devised in the 1500s wasn't so revolutionary—although Copernicus championed a moving earth, he clung unquestioningly to Aristotelian ideals such as circular motion. He wrote: "It is altogether absurd that a heavenly body should not always move with a uniform velocity in a perfect circle." In fact, Copernicus tried to connect to the ancients by writing his most important treatise, De Revolutionibus Orbium (The Revolutions of the Celestial Orbs), which echoed Ptolemy's Amalgaest, with each chapter of his book correlating to a chapter in Ptolemy. Moreover, Copernicus cited pre-Aristotelian philosophers such as the Pythagoreans to support his ideas for a sun-centered universe. To overturn Aristotle, he reached back even farther in time—not what one would call really taking a leap into the unknown.
Not to belittle Copernicus—he certainly provided a jump from the status quo. He also used a new concept to choose his theory: simplicity. Or even, one could say, beauty. The austerity of the simple Copernican system gave it an aesthetically appealing quality missing from Ptolemy's rings within rings. In modern times, scientists have almost deified this simplicity concept, known as Occam's Razor. If two theories fit the data, choose the simpler of the two. If you can explain the cosmos with just a few orbits instead of all those epicycles, then stick to the former.
But, alas for Copernicus, his simple ring system of planets orbiting a slightly off-center sun didn't correspond to reality substantially better than Ptolemy's model. Sticky Mars was still out of whack. Copernicus's De Revolutionibus Orbium was edited by a man named Rheticus, who, legend has it, became so frustrated with mapping the path of the red planet that he called upon the spirit world to help. A demon appeared, threw him against a couple of walls, and shouted, “Thus are the motions of Mars!"
Until someone decided to map the orbit of Mars first and then determine the math that described it instead of the other way around, no one was going to produce a complete model of the sky. That was not something Copernicus, firmly enmeshed in the philosophies of his day, was capable of doing. It was Brahe and Kepler, with their willingness to really observe what they were studying, to insist that the observations match their theories, who nudged cosmology a little closer to modern-day "science."
That these two characters—for they were definitely both characters—had the chance to come together and collaborate is almost beyond belief. Brahe was of Danish nobility, Kepler of the German lower class, but together they provided the most accurate depictions of the stars until that time.
--'The Big Bang Theory: What It Is, Where It Came From, and Why It Works', Karen C. Fox