Catching the Elusive Planet Mercury

By Dennis Mammana

June 20, 2019 4 min read

Week of June 23-29, 2019

Mercury is one of those planets we rarely see.

Unlike Venus, which can dominate our sky with its brilliance, or Jupiter, Mars or Saturn that can shine brightly all night long, Mercury appears for only a few weeks each year and, even then, requires quite a bit of effort to find.

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.

I wouldn't be surprised since, from our terrestrial vantage point, Mercury always appears so close to the sun that it's often lost in its glare. This occurs because Mercury is the innermost world of our solar system, whipping around its orbit once every 88 Earth-days at a distance of only 36 million miles from the scorching face of the sun.

Only when it reaches a significant "elongation" from the sun can we hope to see it, and this occurs only at dusk or dawn. In fact, some of the ancients thought of Mercury as two different bodies. The Greeks, for example, called it "Hermes," the messenger of the Gods, when it appeared in the waning light of dusk and "Apollo," when it shone in the morning before sunrise.

If you've never had the pleasure of spotting this fascinating world, now might be a great time to try.

To find it, head outdoors shortly after sunset and begin scanning low in the west-southwestern sky with binoculars. You may spot Mercury as a fairly bright, flickering "star" only a few degrees above the horizon. About 30-45 minutes after sunset, you should be able to see it with the unaided eye, not far from planet Mars and the bright stars Castor and Pollux.

Keep watch over the next week or so, as Mercury appears to fade significantly as well as descend below the even fainter planet Mars. By July 3, the thin crescent moon will join the scene but will be visible only to those with an extremely low western horizon.

You can aim a small 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 turbulent atmosphere before reaching our eyes.

If you're fortunate enough to see a relatively steady image, you might notice that Mercury now displays a thin crescent phase, not unlike the moon does from time to time.

Mercury is a tiny planet and quite different than any other in our solar system. Because it's much too small and close to the sun to sustain an atmosphere, Mercury's temperature on its daytime side soars to hundreds of degrees and plunges to hundreds of degrees below zero on its nighttime side. And spacecraft photos of this dry, cratered world look remarkably like those of the moon.

If, like the great Copernicus, you've never watched the antics of Mercury, don't miss its brief appearance this week!

 Mercury is one of those planets we rarely see.
Mercury is one of those planets we rarely see.

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