1. Retrograde Motion of the Planets

2. Planetary Motion  Venus and Mercury stay near the Sun.  Can only be seen in early evening, early morning  In comparison, on any given night, Mars, Jupiter and Saturn move westward along with the fixed stars due to Earth’s rotation.  But! At certain times, these planets appear to “wander” against their starry background in a slow, looping motion that lasts several weeks.

3. Retrograde Motion  Def: the movement of an object in the sky from east to west rather than its normal motion from west to east.  A change of direction  Retrograde motion is produced when Earth catches up with and passes an outer planet in its orbit.  Earth is on an inside track and moves faster than outer planets.  Think of a 400m track.

5. Retrograde Motion  Every time Earth catches up to an outer planet and moves between the outer planet and the Sun, the planet appears to make a loop.

6. Copernican Model – Retrograde Motion

7. Watch this (it will make much more sense!)  Retrograde motion:  http://www.youtube.com/watch?v=72FrZz_zJFU http://www.youtube.com/watch?v=72FrZz_zJFU  Also interesting…  Relative size of stars and planets  http://www.youtube.com/watch?v=7T1LO6nOUdw&feature=rel ated http://www.youtube.com/watch?v=7T1LO6nOUdw&feature=rel ated