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Nightfall’s Fabulous Conjunction

Mercury joins Mars in its last hurrah

For more than a month now, Mars has been clinging to the southwest horizon in evening twilight. The next couple weeks are your last chance to spot our red neighbor, which has been a fixture in the night sky for more than a year and a half. But he goes out in style, joined this week by much brighter Mercury in a spectacluar conjunction.
    In the early evening of the 7th, within a half-hour of sunset, you’ll find the two planets separated by less than three-quarters of a degree low in the west-southwest. Mars is the higher of the two, but at –1 magnitude, Mercury is more than four times brighter than +1 magnitude Mars, which is still as bright as all but the strongest stars.
    Friday evening, the gap closes to one-half degree, with Mars still a little higher. They are so close that the two appear together within binoculars or even a telescope. By Saturday the planets have swapped positions, with Mercury now more than one degree above ruddy Mars. Come Sunday they are still close, and on Monday they are joined by the ever-so-thin waxing crescent moon. But in following nights, Mars plummets toward the horizon. Mercury, however, arcs higher until reaching greatest elongation — its farthest point from the sun — on the 17th before making its own exit from our night skies.
    Week’s end marks the tail of the current Globe At Night observing session. The goal is to “raise public awareness of the impact of light pollution by inviting citizen-scientists to measure their night sky brightness and submit their observations to a website.” The commons targets are the constellations Leo, Crux and Orion — the quarterback, as I now think of that grand celestial figure (Woo-hoo Joe Flacco!).
    You’re asked to record how many stars you can see within one of the constellations as compared to star charts at the organization’s website. Up for the challenge? Go to www.globeatnight.org.