Thursday, February 4, 2010

Why Mars is bright

A few days ago (January 29), I posted about how Mars was nice and bright and located near the full Moon.  Mars has been about as bright as the star Sirius which is the brightest true star in the sky (planets sometimes get a little brighter).  A student asked me today why Mars was so bright lately.  The following figure should illustrate the reason:
Looking down on the inner solar system, we see that Mars and Earth are lined up on the same side of the Sun.  Astronomers would say that Mars is at opposition (opposite from the Sun).  It's relatively close to us and catching lots of sunlight to reflect back so we can see it so brightly as a reddish "star" in the night sky.

It's currently in the constellation of Cancer, halfway between Regulus in Leo and Castor and Pollux in Gemini (about half-way up in the eastern sky around 8 pm in our area).  Go out and take a peek, it's unmistakable.

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