Mars is approaching Earth in our morning sky, and as it does, it will drift past the glittering stars of the M35 star cluster on the morning of Aug. 29, just as it did in March 2008, as shown in this image. But don't expect Mars to appear as large as the full moon, as an Internet hoax would have us believe.

Jimmy Westlake/courtesy

Mars is approaching Earth in our morning sky, and as it does, it will drift past the glittering stars of the M35 star cluster on the morning of Aug. 29, just as it did in March 2008, as shown in this image. But don't expect Mars to appear as large as the full moon, as an Internet hoax would have us believe.

Jimmy Westlake: Planets of fire and ice

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Jimmy Westlake

Jimmy Westlake's Celestial News column appears Tuesdays in the Steamboat Today.

Find more columns by Westlake here.

— Fire and ice. These two words succinctly describe the difference between the two terrestrial planets Mercury and Mars, both of which are visible in Colorado skies this month.

Mercury, our solar system's innermost world, bakes under a sun that is only 35 million miles away and looms three times larger than in earthly skies. Daytime temperatures on the surface of Mercury can reach a blistering 800 F, while the nighttime low can dip to minus 300 F. This staggering 1,100-degree diurnal variation in temperatures is in part because Mercury has no atmosphere to insulate its surface and in part because of a very slow rotation on its axis. One solar day on Mercury lasts for 176 Earth days. This might be the last place you would expect to find ice, but that's exactly what astronomers think they have found in the floors of some deep craters near Mercury's poles. When NASA's MESSENGER spacecraft drops into orbit around Mercury in March 2011, it will try to confirm this suspicion. MESSENGER will make one more close flyby of Mercury on Sept. 29 before it returns in March 2011 for final orbital insertion. You can spot Mercury this month low in the western sky as it reaches its greatest angle east of the sun Monday. See if you can spot Mercury and Saturn just to the right of the crescent moon Saturday evening, about 30 minutes after sunset. Mars has been hovering in the distance on the far side of the sun from Earth for the past several months, but the gap between the two planets is shrinking, and the Red Planet now is growing brighter in our predawn sky.

Daytime temperatures on Mars struggle to get above freezing, even in the summer months at its equator, and at night, the thermometer regularly plummets to near minus 200 F. Earth will pass closest to Mars, at the safe distance of 61.7 million miles, near the time of its next opposition Jan. 29.

I've had many excited people calling me recently to find out when they can go outside and see Mars "as big as the full moon," as described in an e-mail that is circulating around the Internet. Truth is, this is the same e-mail hoax that has been making the rounds every summer since 2003, getting folks all excited about a once-in-a-lifetime opportunity for an eye-popping view of Mars. Let me be very clear: Even when as close to the Earth as possible, Mars can never appear as anything other than a bright point of light without the aid of a telescope. So, we'll all have to be satisfied with seeing Mars as that bright reddish "star" that wanders through our night sky. Catch Mars in the early morning before sunrise this month as it drifts through the stars of Taurus and Gemini. On Aug. 29, watch Mars with your binoculars as it drifts past the glittering star cluster M35.

Professor Jimmy Westlake teaches astronomy and physics at Colorado Mountain College's Alpine Campus. He is an avid astronomer whose photographs and articles have been published all around the world. His "Celestial News" column appears weekly in the Steamboat Today newspaper and his "Cosmic Moment" radio spots can be heard on local radio station KFMU. Also, check out Jimmy's astrophotography Web site at www.jwestlake.com.

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