1. Johannes Kepler’s Planetary Discoveries Jacqueline DePue

2. Thinking Before Kepler’s Discoveries Many astronomers theorized about the planets and stars in the nighttime sky. As astronomical technology increased in accuracy, so did the theories of planetary motion which were mostly driven from observation.

3. PlatoEudoxus 4 th century BC  Plato based planetary motion off of observation and senses: there is no wind and no objects are flying off Earth, therefore Earth is not moving.  He argued that Earth was stationary at the center of the universe and that the sun, moon, and planets revolved around Earth in perfect circles (Celestial Spheres) at a constant velocity.  Eudoxus was a student of Plato.  He also claimed that the solar system was Earth- centered, but it had 26 crystalline spheres to account for motions of the planets, moon, and sun.

4. Hipparchus Ptolemy 2 nd century

5. CopernicusTycho Brahe 1500s  Brahe was well known for his improvements of astronomical instruments which collected extremely accurate data.  However, Brahe tried to disprove Copernicus’s heliocentric theory by explaining that the stars should appear to move due to parallax.  He attempted to measure parallax but could not, therefore he concluded that the Earth was at the center of the universe.

6. Forming His Beliefs Johannes Kepler was born in southwest Germany in 1571. In 1576, he entered Latin school and by 1589 had begun his education as a university student at the Protestant University of Tübingen. Kepler’s most noted mathematics teacher was Michael Maestlin, an astronomer that supported the newer heliocentric theory proposed by Nicolaus Copernicus. At the university Maestlin had to teach the Ptolemaic model. However, Maestlin was able to show his graduate students (one of them being Kepler) Copernicus’s heliocentric system. At this time, Kepler called himself a Copernican for “physical or, if you prefer, metaphysical reasons.”

7. The Cosmographic Mystery

8. Planetary Motion Tycho Brahe, a renowned creator of scientific instruments and observer of the heavens, had collected many observations of the nighttime sky with his high-tech instruments and hired Kepler to deduce new orbits for the planets. Kepler’s main duty was to determine the orbit of Mars…however, he first had to determine the orbit of Earth.

9. The Orbit of Earth Although Brahe believed that the sun orbited the earth and the other planets orbited the sun, Kepler disagreed. Kepler used both Copernicus’s idea that the planets orbit the sun and Copernican values for the periods of the planets. These values were sets of data points, each separated by 687 days which was known to be one Martian year.

10. Law of Equal Areas

11. Law of Ellipses

12. Law of Periods

13. Although there were many theories, each built upon the previous one and new observations made. Kepler’s theories were proposed after Tycho Brahe hired him as an assistant.

14. Impact on Society Through his extensive research, recorded observations, and mathematical calculations, Kepler was able to determine three important laws regarding planetary motion: 1.Law of Equal Areas 2.Law of Ellipses 3.Law of Periods

15. As a Result… Some questions still remained regarding Kepler’s planetary laws:  What force creates the elliptical paths of the planets?  What makes the planets move? Sir Isaac Newton, an upcoming physicist and mathematician, would have been able to prove all of Kepler’s laws through his law of universal gravitation.

16. Gravity is Introduced Even if Kepler had not provided the information he learned about the planets and their motions, Newton still could have predicted his law of universal gravity. However, the important result of Kepler’s laws were that Newton’s proposal of gravity strengthened the laws, mainly the Law of Periods, and made them more accepted in the scientific community. Finally, the remaining questions Kepler left unanswered were resolved: gravity is the force that makes the planet’s orbits elliptical and makes the planets move. Overall, Kepler’s laws of planetary motion heavily supported the new idea of gravity.

18. References Anderson, Scott R. "The Motion of the Planets." Open Course : Astronomy : Introduction : Lecture 5 : Motion of the Planets. The Gateway to Educational Materials, 2002. Web. 26 Feb. 2014. Retrieved from. "Mars' Orbit Is Not a Circle." Mars' Orbit Is Not a Circle. Door to Science, 2007. Web. 27 Feb. 2014. Retrieved from. "Medieval & Renaissance Astronomy up to Newton." Australia Telescope National Facility. CSIRO, 2 Jan. 2014. Web. 26 Feb. 2014. Retrieved from. "The Galileo Project: Johannes Kepler." The Galileo Project | Science | Johannes Kepler. N.p., 1995. Web. 26 Feb. 2014. Retrieved from.