Sunday, May 11, 2008

Passing Mars

Earth orbits around the sun a bit more quickly than Mars. Most of the time, the apparent motion of Mars, as seen from Earth, has Mars slowly making steady progress across the background starfield. Over the past few months, however, Mars has appeared to be traveling backwards. This is because Earth caught up to, and passed the point of Mars orbit around the sun. The Astronomy Picture of the Day has an annotated version of this photo. It's an interesting astronomical phenomenon.

See Mars from Whidbey Island.


Bunk said...

Aw B.S. Mars can't travel backwards any more than... ooh... wait... it is! How'd you do that?

David said...

Mars' retrograde motion lead Johannes Kepler to discover that all planets have elliptical,and not circular, orbits. It's a pretty interesting story, actually.

His mentor, Tycho Brahe, believed that the problem of Mars' retrograde motion was unsolvable, so he gave it to Kepler to keep him out of the way. That backfired, however, because it was exactly the information Kepler needed to prove his theory.

Cool post, Dad!

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