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The Motion of Mars: Part 4


Today we will conclude the astronomical tale of how the motion of Mars arguably sparked the origin of modern astronomy and science.  Last week we discussed how Nicolaus Copernicus presented a heliocentric, or Sun-centered, model of the universe with the all the planets, including Earth and Mars, orbiting the Sun.  But Copernicus’ model was not well received because it did not predict the positions of the planets much better than Ptolemy’s geocentric, or Earth-centered, model, and religious influences during the time period also wanted to maintain that the Earth was the center of the universe.  But enough people were intrigued enough by the heliocentric model that they continued a pursuit of which model was correct.  Tycho Brahe, still today considered the greatest naked-eye astronomer of all time, collected fresh data for the positions of Mars and the other planets as they moved against the background stars.  With this data, Tycho worked with Johannes Kepler, a German mathematician, to determine a correct model for the universe.  Ultimately Kepler was able to figure out that the planets orbited the Sun not in perfect circles, as previously assumed by others like Copernicus, but as ellipses.  Galileo Galilei reinforced this helio-centric model by observing a full set of phases for Venus, which could only be observed if Venus and Earth orbited the Sun.  It wasn’t until Isaac Newton, though, that anyone was able to answer the question “why would Mars and other planets orbit the Sun way they do?”  Kepler guessed it was a magnetism, but Newton determined it was the force of gravity producing the planetary motions observed; Newton also invented calculus to help prove that determination!  And thus the nature of the solar system and the universe was headed down the correct path, and the foundations of the scientific method were strengthened, all because of the mysterious motions of Mars!


Follow your curiosity to the Fred G. Dale Planetarium at Wayne State College.

Dr. Todd Young hails from Minnesota and received his undergraduate degree in Physics & English from the University of Minnesota – Morris, his Master’s degree in Physics from Purdue University, and his Ph.D. from the University of Nebraska – Lincoln in Astrophysics. He has worked at Wayne State College since receiving his doctorate in 1998 and is currently a full professor of physics and astronomy. He teaches a variety of courses at Wayne State College, including university physics, astronomy, general education science, and astrophysics.
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