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Use Venus to find Mercury in March

For the Northern Hemisphere, this month presents the best evening apparition of Mercury for the year. Moreover, you can use the dazzling planet Venus, the third-brightest celestial object after the sun and moon, to find Mercury, the solar system’s innermost planet. Both Venus and Mercury are emerging from the sunset glare day by day, and these two worlds should become visible at evening dusk in a week or so. Some intrepid sky watchers might even catch Venus and Mercury after sunset this evening, on March 3.

Do you have binoculars? They’ll come in handy, as Venus and Mercury are only a little more than one degree apart for the next several days. (One degree is about the width of your little finger at an arm length.) But that’s not all. Venus and Mercury will remain close enough together on the sky’s dome to fit inside a typical binocular field of 5o for the first three weeks of March 2018. So if you spot Venus, but not Mercury, aim binoculars at Venus to see both worlds taking stage in the same binocular field.

Find a unobstructed horizon in the direction of sunset, and then seek for Venus and Mercury near the sunset point on the horizon around 30 to 40 minutes after sundown. At mid-northern latitudes, Venus and Mercury set about one hour after sunset. At the equator, the twosome sets about 45 minutes after the sun; and at temperate latitudes in the Southern Hemisphere, Venus and Mercury barely stay out longer than one-half hour after the sun goes down. Click here for a sky almanac that’ll give you Venus and Mercury’s setting times for your sky.

By the way, Mercury isn’t difficult to see because it’s dim. Although Venus is about 12 times brighter than Mercury, the innermost planet is actually the third-brightest celestial object to light up the (very early) evening sky right now, as it’s just a touch dimmer than Sirius, the brightest star of the nighttime sky. However, Mercury has to contend with the dusky thickness of the Earth’s atmosphere near the horizon. Binoculars, though, can help you to reel in Mercury from the evening twilight.

Throughout the month, Mercury will dim somewhat (because of its waning phase). Even so, Mercury will climb up higher up in the sky at sunset and stay out longer after sunset. Venus will do likewise. So both worlds should be easier to view later this month. In fact, Mercury will reach its greatest eastern elongation (maximum angular distance from the setting sun) on March 15, 2018. At that juncture, Mercury and Venus will stay out about 80 minutes after the sun at mid-northern latitudes.

Last but hardly least, watch for the young waxing crescent moon to sweep by Mercury and Venus on March 18, 19 and 20, as shown on the sky chart below. Think photo opportunity!

Look for the young waxing crescent moon to pair up with the planets Mercury and Venus on or near March 18, 2018!

In the meantime, we’ll be eagerly awaiting to see how many EarthSky viewers will catch the two inferior planets – Venus and Mercury – after sunset on March 3, 2018.

Bruce McClure

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