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27 Feb 2017

March Astronomy: Venus Appears at Both Dawn and Dusk on Some Days, as the Planets Continue Their Cosmic Dance

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This month’s selection of happenings includes the last evening and first morning appearances of Venus; the year’s most favorable apparition of Mercury; early evening moonrises; simultaneous views of planets low above opposite horizons (Mars-Jupiter and Mercury-Jupiter in the evening, with Venus-Jupiter in the morning); and a bright, far southern star, Canopus, reaching its high point very low over our southern mountains.

Venus is still very prominent in the evening sky as this month opens, setting in a dark sky 2 1/2 hours after sunset on March 1. By March 17, Venus sets just one hour after sunset, and by March 21, Venus drops below the horizon barely half an hour after sunset. By that date, Venus is already rising ahead of the sun, and it’s possible to observe it at both dusk and dawn for a few days. Through a telescope or even 7-power binoculars, the planet displays a crescent—best observed in daytime, or in bright twilight.

Our evening sky chart plots daily positions of the brightest objects in the sky at mid-twilight, when the sun is 9 degrees below the horizon, about 40 minutes after sunset. As March begins, the most prominent objects, in order of brightness, are Venus in the west; Sirius in the south-southeast; Canopus very low, just east of due south; Capella just north of overhead; and Rigel in the south. As March runs its course, Venus descends the near side of her orbit and drops below the western horizon, but not before Mercury climbs into view on the far side of his orbit. For a few evenings, both planets are visible. They appear closest to each other on March 18, with emerging Mercury passing 8.5 degrees south (to the lower left) of departing Venus. In the eastern sky just before month’s end, bright Jupiter rises a few degrees south of due east, while golden Arcturus rises in the east-northeast.

Sirius and Capella mark extreme south and north vertices of the huge “Winter Hexagon,” with Betelgeuse and Orion’s belt inside. The belt points the way to Sirius, and in the opposite direction, to Aldebaran. Preceding the Hex across the sky in March is faint Mars, itself preceded by Venus or Mercury, or both planets for a few days starting in midmonth. The trailing Pollux-Procyon side of the Hex reaches due south at mid-twilight at the end of March. Following them is Regulus, heart of Leo, Still farther east, we find Jupiter and Arcturus rising into view later in the evening, or by mid-twilight at month’s end.

In morning twilight: Jupiter, in the southwest to west-southwest as dawn brightens, ranks first in brightness, until Venus emerges north of east late in the month. Before the sky brightens too much, note Spica 4-6 degrees to the lower left of Jupiter. The most prominent stars are golden Arcturus high in the west-southwest to west, far to the upper right of the Jupiter-Spica duo, and blue-white Vega, very high in the northeast. Next in brightness is steady yellow Saturn, in the south-southeast to south. Look also for Altair and Deneb, completing the Summer Triangle with Vega. Find twinkling reddish Antares to the west and south of Saturn.

On March 1, the 15 percent crescent moon appears well to the upper left of Venus and a few degrees left of Mars. The moon climbs much higher each evening, and on Saturday, March 4, the nearly half-lit moon will occult, or cover, the bright star Aldebaran, with a sudden disappearance behind the moon’s leading dark edge slated for 7:12 p.m., and reappearance for 8:30 p.m. Binoculars and maybe even the unaided eye will suffice for the first event, but a telescope will be required to catch the star’s reappearance at the moon’s bright edge.

The moon continues to march eastward, passing between Procyon and the Gemini twins, Pollux and Castor, by March 7, and getting past Regulus, heart of Leo, by the evening of March 10. On Saturday evening, March 11, the almost-full moon rises at 5:14 p.m., still before sunset, which occurs at 5:51 p.m. Remember to set your clocks one hour ahead, and you won’t be surprised by Sunday’s later sunset at 6:52 p.m., and moonrise (just past full) at 7:13 p.m. After moonrise on Wednesday, March 15, look for bright Jupiter nearby, with Spica just a few degrees to the lower right.

With daylight saving time shifting our sunrises an hour later, predawn sky-watching becomes more attractive. Look an hour before sunrise on March 14 and 15 for the waning gibbous moon with Jupiter nearby, in the southwest to west-southwest. Spica is to Jupiter’s lower left. On the weekend of March 18-19, find reddish twinkling Antares near the moon in the southern sky, with brighter, steady Saturn to their left. On Monday morning, March 20, the moon, nearly at last quarter phase and just over half full, will appear closely to the upper left of Saturn. A telescope reveals the planet’s amazing rings, tipped nearly 27 degrees from edge-on this year, the greatest angle possible.

See Venus at both dawn and dusk for a few days! Around March 20, start trying to observe Venus rising before the sun, even though it’s still also visible in the evening, setting after sunset. Binoculars will reveal Venus as a large, thin crescent, as little as 1 percent illuminated on March 23-26.

On March 25, at 6:22 a.m., about 20 minutes before sunrise, find the thin (8 percent) old crescent moon 12 degrees up in the east-southeast. Locate Venus 32 degrees farther left and 10 degrees lower, or 10 degrees north of east and only 2 degrees up. This is the day Venus appears at inferior conjunction, an unusually wide 8.3 degrees north of the sun and 1 percent illuminated. On Friday, March 26, at 6:21 a.m., find the 3 percent crescent moon 12 degrees south of east and 4 degrees up.

The young lunar crescent first appears in the evening on Tuesday, March 28, around 7:29 p.m., nearly due west, just 5 degrees up and a few degrees to the lower left of bright Mercury. The next evening, March 29, look for the 5 percent crescent moon 40 minutes after sunset, 15 degrees up and to the upper left of Mercury. As twilight deepens, look for dim Mars about 10 degrees above the moon and a little right. By Thursday evening, March 30, the moon will climb to the upper left of Mars. Watch for Jupiter rising 7 degrees south of east just more than half an hour after sunset. Can you observe the three evening planets, Mercury, Mars and Jupiter, simultaneously?

The Astronomical Society of the Desert will host the next in our series of monthly star parties on Saturday, March 4, from 6 to 9 p.m., and on Saturday, April 1, from 7 to 10 p.m. They are held at the Visitor Center of the Santa Rosa and San Jacinto Mountains National Monument, on Highway 74, within 4 miles south of Highway 111 in Palm Desert. Check www.astrorx.org. The next high-altitude star party at Sawmill Trailhead (at 4,000 feet—wear warm clothes!) will be held Saturday, March 25. Also, check the link to our “Impromptu Star Parties,” which could be announced on short notice at any time.

Robert C. Victor was a staff astronomer at Abrams Planetarium at Michigan State University. He is now retired and enjoys providing skywatching opportunities for school children in and around Palm Springs. Robert D. Miller did graduate work in planetarium science and later astronomy and computer science at Michigan State University and remains active in research and public outreach in astronomy.

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