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Saturday, May 23, 2015

Earthsky Tonight – January 28, 2010: Does Mars ever appear as large as the full moon?

Courtesy of EarthSky
A Clear Voice for Science

Mars big and bright
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Tonight, the planet Mars will be at at its biggest and brightest until the year 2014. Does that mean that Mars will be as large as the moon tonight?

Check it out for yourself. This evening, look to the lower left of tonight’s almost-full waxing gibbous moon for a ruddy-colored “star.” That “star” is actually Mars, the 4th planet outward from the sun, shining most brightly in Earth’s sky for several years to come. Even so, Mars is nowhere as the large as the moon. The diameter of the moon spans over 1/2 degree, whereas Mars’ diameter measures only 1/140th of the moon’s diameter. In other words, you would have to line 140 Mars side by side to equal the diameter of the moon.

Without doubt, many of you will receive an email later this year, telling you that Mars will appear as large as the full moon on August 27. Don’t believe it! Mars will be even smaller and fainter in August 2010 than it will be tonight.

However, on August 27, 2003, Mars came marginally closer to Earth than it had since Stone Age times. But even if Mars were to come that close to the Earth tonight, its diameter would only be 1/80th the diameter of tonight’s moon.

Written by Bruce McClure

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