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The Sky This Week, 2012 March 27 - April 3

Elongation for Venus, swan song for Jupiter.


The Moon, Venus, & Jupiter
Imaged 2012 March 26, 19:50 EDT
at the U.S. Naval Observatory

The Moon climbs rapidly in the western sky this week, arcing high through the stars of the Great Winter Circle before entering the more sparsely populated springtime constellations. First Quarter occurs on the 30th at 3:41 pm Eastern Daylight Time. Luna pulls away from Venus and Jupiter, perching between the Pleiades and Hyades star clusters on the evening of the 27th. On the 29th she passes well north of the bright stars of Orion, and on the 31st forms an almost perfect line between Procyon in Canis Minor and the Twin Stars of Gemini, Castor and Pollux. Luna wraps up the week passing nine degrees south of ruddy Mars on the night of April 3rd.

We’ll have to wait quite a while before we see as dazzling a gathering of planets in the western twilight sky as we have seen for the past few months. Now that Venus has left Jupiter in her wake the duo seem to go their separate ways, and their next close conjunction at such a prominent altitude in the evening sky won’t occur until the year 2036. However, early risers in the midsummer months will have a chance to enjoy the pair in close proximity in the morning sky for several weeks in late June and July before they ultimately part company. They will meet about once each year, either before dawn of after sunset, between now and 2036, but most of these encounters will occur in twilight within 15 degrees of the horizon. Favorable evening elongations of Venus, similar to the one she’s undergoing now, occur at eight year intervals, while Jupiter takes about 12 years to go once around the sky. Thus every third favorable elongation of Venus occurs when Jupiter has completed two orbits, and a dramatic conjunction occurs high in the post-twilight sky. Yes, the end of March 2036 should be quite spectacular, with Mercury, Venus, Mars, Jupiter and the Moon all visible in the western sky for your entertainment. Better mark those calendars now!

Getting back to the present, time is rapidly running out on Jupiter for the current apparition. Even though Old Jove is visible in the west almost immediately after sunset, by the time there’s enough contrast in the twilight sky to view him in the telescope he is wallowing in the turbulence boiling off the western horizon. Trying to find detail on his surface is a bit like trying to read a book that’s located on the bottom of a swimming pool. By mid-April he sets at the end of evening twilight, and by early May he’s too close to the Sun to observe. You won’t have to wait too long to see him again, though, since he’ll rise in the wee hours beginning in the summer months.

Venus continues to climb higher in the evening sky, reaching her greatest elongation east of the Sun on the 27th. She will continue to pace Old Sol’s eastward progression through the stars for several more weeks before she begins to gradually begin slipping back toward the day-star. Through the telescope her disc resembles a featureless first-quarter Moon, and as the weeks progress her apparent diameter will increase as her phase begins to slim to a crescent.

Mars is seemingly in Venus’ sights as the dazzling planet presses eastward against the stars, but before Venus can get close to the red planet she will drop from the sky like a stone. Mars continues to drift westward among the stars of Leo, the Lion, and even though he’s barely a month past opposition he’s already dropped half a magnitude in brightness and lost a full arcsecond of apparent diameter. Mars has been a difficult target to observe during this current opposition, but amateur astronomers equipped with modern CCD camera technology and powerful image-processing tools are still obtaining images comparable to those from the spectacular close oppositions of 2003 and 2005. Mars’ thin atmosphere has been particularly active this year, with many spectacular cloud formations appearing in amateur images.

As April opens the planet Saturn prepares for his opposition appearance in the middle of the month. The ringed planet now rises at around 8:30 pm, and you can get a decent view of him a couple of hours later as he shares the southeastern sky with the bright star Spica. The two form an interesting pair in an otherwise sparsely-populated part of the sky. Saturn’s rings are now tipped about 17 degrees to our line of sight, so even a good three-inch telescope should reveal the Cassini Division that bisects the brighter sections. A six-inch telescope should reveal several of the planet’s icy moons as well. When you tire of trying to eke out detail on Mars, Saturn will be a fine reward for your patience.

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