Seeing may be believing, but believing is not necessarily understanding. A most important puzzle was misunderstood for nearly 1400 years. As viewed from Earth, Mars sometimes appears to change direction and move backward. Ptolemy in around 150 A.D. explained the observations with Mars orbiting Earth. The only problem was that Mars had to periodically go through smaller orbits within its main orbit around Earth. This felt right, but was complicated and of course was incorrect. No harm no foul, unless a correlation with the dark ages is found.
Eventually Kepler in the 16 hundreds gave a simpler explanation for Mar's sometimes backward motion. He put the sun at the center of the solar system. The fact the Earth moved faster with a shorter orbit explained everything.
Mar's apparent motion is determined by the line passing through Mars and Earth.
The point (D,y) is a point
on the line determined by P1 and P2. It moves up,down, and then back up as Earth
passes Mars. The motion against the background of stars is what gives Mars the
appearance of changing direction. A problem lasting centuries is explained in
part by the simple equation of a line.
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Instant Physics, by Tony Rothmon, PH.D. |
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