Owen Gingerich is the author of one of my favorite books, "The Book Nobody Read", which was my Pick for October 2004 (could it have been that long ago?), which combines astronomy, history research, and bibliophilia. In the current (September, 2011) Physics Today, he clearly but briefly describes the scientific questions that were answered by the observations of Tycho Brahe and the calculations of Johannes Kepler. Brahe's observations were made without telescopes, of course (in 1593, there were no telescopes); his measurements were instead done with a large, high-precision sextant-like instrument called an "equatorial armillary" that he designed and built himself. Kepler was an out-of-work Lutheran high school teacher whose job was a casualty of the Catholic counter-reformation. These guys were able to determine the distance between the Earth and Mars by using geometry and the parallax effect. This article was especially meaningful to me because I was able to visit Brahe's underground observation on the island of Hven during a science history tour in 2007.