Jimmy Westlake: Don’t miss Mercury
April 29, 2009
Almost everyone has seen the planet Venus gleaming in the sky as the “evening star” or the “morning star.” Most people probably have spotted brilliant Jupiter or ruddy Mars when dominating the night sky. Many folks might have even found Saturn shimmering against the stars. The one naked-eye planet that most folks probably have not seen is the illusive planet Mercury.
Our solar system’s closest planet to the sun, Mercury, also became the solar system’s smallest planet after little Pluto was demoted in 2006. Both of these items on Mercury’s resume account for its illusive nature.
First, it is small, so it does not reflect very much sunlight our way and doesn’t appear as bright as the other planets in our night sky. Furthermore, as it swings around the sun and approaches Earth, Mercury turns its darkened nighttime hemisphere toward us, causing it to fade.
Second, because it orbits so close to the sun, it moves very fast in its orbit and zips through our sky in only a couple of weeks and then vanishes. It’s no wonder the Romans named it after their swift messenger god! Also, because it hugs the sun so closely, it never wanders very far from the sun in our sky. It always rises or sets within an hour and a half of the sun and seldom is seen in a completely darkened sky. Mercury is the “twilight planet.”
Several times each year, Mercury swings out far enough from the sun that we can get a good peek at it, sometimes in the morning sky, and sometimes in the evening sky. These times of greatest elongation, as they are called, are the times you want to try to spot the innermost planet.
The best evening elongation of Mercury this year is in progress now. You can glimpse it any time in the next week or so, setting shortly after the sun in the west-northwest sky.
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A particularly beautiful sight greeted lucky sky watchers Sunday evening when the waxing crescent moon joined Mercury and the Pleiades star cluster, visible through breaks between the snow clouds. During much of this evening apparition, Mercury will be hanging out near the Pleiades star cluster (also called the Seven Sisters). Binoculars will help pull in the glittering star cluster beside the much brighter planet Mercury. Having reached its greatest elongation 20 degrees east of the sun Sunday, Mercury now will slowly descend toward the sun and the horizon a little earlier each night until it is swallowed by the sun’s glare in mid-May.
Consider yourself very fortunate if you catch sight of Mercury, the illusive “twilight planet” this month. Some of history’s greatest astronomers, including Nicolaus Copernicus, are said to have never been so fortunate.
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 Pilot & Today. His “Cosmic Moment” radio spots can be heard on local radio station KFMU. Also, check out Jimmy’s Web site at http://www.jwestlake.com.
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