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Spotting Mercury, the Messenger
Week of May 3-9, 2015
In Roman times, it was known as the god of commerce, travel and thievery. The Greeks called it Hermes, the messenger of the Gods, when it appeared at dusk and Apollo when they saw it at dawn.
Today we know it as Mercury — the nearest planet to the sun — and it's back in our evening sky this week for all to enjoy.
If you've never seen Mercury, you're certainly not alone. Many stargazers have never spotted it, including the great 16th-century Polish astronomer Nicolaus Copernicus. But, since this week marks the year's best opportunity for Northern Hemisphere stargazers, now's the time to check out this elusive planet.
I call Mercury "elusive" because it whips around the sun in only 88 days and, as a result, it never stays in our sky for long, and never strays far from the sun's glare. Even under the most ideal conditions, we can never see Mercury more than 28 degrees from the sun, which means it cannot ever appear in a completely dark sky.
This week, however, you can find the planet as long as clear weather extends all the way to the horizon at dusk.
Shortly after sunset, you'll see a brilliant light midway up in the western sky. It's been there for a few months already; that's the planet Venus. Now, with your eyes or binoculars, scan below and to its right low Mercury will appear as a much fainter star-like object in that part of the sky, and will be shining with a distinctly yellowish cast.
And don't be surprised if it twinkles; the thick column of air through which its light must pass will do that even to a planet, despite what we might have learned in school.
Mercury is a world quite different than all others in our solar system. Spacecraft photos of this dry, cratered world look remarkably like those of the moon. Because it's much too small and close to the sun to have an atmosphere, temperatures on its daytime side soar to hundreds of degrees, and on its nighttime side plunge to hundreds of degrees below zero.
Now, while it's true that Mercury is the closest planet to the sun, it isn't the hottest of our planetary family. That honor belongs to Venus; even though it lies twice as far from the sun as Mercury, its thick cloud cover acts as a blanket and holds the planet's temperature at a toasty 900F — hot enough to melt lead.
If the western sky is clear at dusk this week, try aiming a small telescope in the direction of these two planets, but don't expect to see much.
Venus, of course, is a good place to start; it will appear significantly larger than Mercury and, this week, will appear nearly in a quarter phase.
Mercury is relatively small, some two and a half times smaller than the Earth, and its light will be significantly distorted by air turbulence near the horizon. But if you're fortunate enough to see a steady image, might notice that Mercury appears not round but rather in a thick crescent phase.
Visit Dennis Mammana at www.dennismammana.com. To read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.
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