Sky Watch: Spotting the elusive Mercury
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Amazing how things from our childhood can stick with us throughout our lives.
I was in fourth grade when I learned that Mercury is the nearest planet to the sun, and that it orbits only 36 million miles from our star's scorching face. Pretty heady stuff for a 9 year old. But it wasn't until many years later that I actually got a chance to see Mercury for myself.
Part of the delay came because the planet is quite elusive and can never be seen in a completely dark sky. Its 88-day orbit around the sun causes it to swing from dawn to dusk, or from dusk to dawn, just about every month and a half. And this means that one has to be outdoors at just the right time -- and with sky conditions just right -- to see it.
Its elusiveness is legendary; it's been said that the great 16th-century Polish astronomer Nicolaus Copernicus -- who overturned the long-held notion that the Earth occupied the center of our planetary family -- had never actually seen this world with his own eyes. Now I can't say whether this is true, but it certainly makes sense given what we know about weather conditions in Eastern Europe and how tricky this world is to see.
Well, the next two weeks provide us an opportunity to do what the great Copernicus could not. In fact, this might be our best opportunity of the entire year to see Mercury.
To find it, head outdoors not long after sunset and begin scanning the western-northwestern sky with binoculars. You may spot Mercury as a bright, flickering "star" only about 10-15 degrees above the horizon. About half an hour after sunset, you should be able to see it with the unaided eye, not far beneath and to the right of the bright planet Jupiter. And here, in the same part of the sky, you'll be seeing the largest and smallest planets of our solar system.
Over the next couple of weeks, Mercury will move slightly among the more distant stars, but on May 31 we'll have an easy shot at finding it. Not long after sunset that evening, look for Mercury to lie to the north of the thin crescent moon -- a delightful sight in binoculars during the waning light of dusk.
By the following night, the moon will have moved along its orbit and will appear just to the southwest of Jupiter.
You can also try aiming a small, low-powered telescope in its direction, but you may be disappointed by what you see. First off, this planet is rather small -- barely the size of the continental United States. And secondly, its appearance near the horizon means that its light must pass through a tremendous amount of distorting atmosphere before reaching our eyes.
If you're fortunate enough to get a relatively steady image, you might check it out with a higher-powered eyepiece. You'll then notice that Mercury appears not as a circular disk but as a tiny thin crescent.
It took me many years to finally catch a glimpse of this elusive planet, but, believe me, it is well worth the effort!