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The Sky This Week, 2010 March 30 - April 6

A star winks out, bright planets parade.
mars12_100320_0259_01small.jpg sat12_100320_0241_01small.jpg
MARS, 2010 MAR 20, 02:59 UT SATURN, 2010 MAR 20, 02:41 UT
Images made with the USNO's 12-inch (30.5-cm) f/15
Clark/Saegmüller refractor

The Moon wanes in the late evening and early morning sky this week, diving southward along the Ecliptic to strike a path through the late-rising summertime constellations.  Last Quarter occurs on April 6th at 5:27 am Eastern Daylight Time.  During the morning hours of April 3rd Luna lies within one degree of the ruddy star Antares, heart of Scorpius, the Scorpion.  About an hour and a half after the Moon rises, beginning at 1:50 am EDT, Luna will pass in front of the third-magnitude star Al-Niyat, one of two prominent stars that flank Antares.  Just over an hour later, at 2:56 am, the star will re-appear from behind the Moon’s dark limb.  This event is best observed with binoculars or a small telescope, and gives a nice demonstration of Luna’s ever-changing position against the background stars.

As the Moon wends her way into the morning sky, the late evening plays host to spring’s arriving constellations.  The bright star Arcturus beams in the eastern sky, while the stars of the Great Winter Circle begin to wink out in the west.  High in the northeastern sky you’ll find the familiar seven star asterism we call the Big Dipper, part of the much larger constellation of Ursa Major, the Great Bear.  The two stars at the end of the Dipper’s “bowl” point in the direction of the North Star, Polaris as you face northward.  Follow their line to the south and you’ll run into Regulus, the bright star marking the heart of Leo, the Lion.  Under dark skies the region of the sky bounded by Arcturus, the Dipper, and Leo is awash with hundreds of faint smudges of ghostly light that generally can be seen with modest telescopes.  These smudges are the glimmers of far-off galaxies belonging to the Virgo Cluster, of which our Milky Way is an outlying member.  This “Realm of the Nebulae” is one of the favorite targets for amateur astronomers in the warming nights of early spring.

Evening twilight provides a very special treat this week, as the fleet planet Mercury seems to leap into the sky to join the dazzling planet Venus.  The two planets spend the entire week separated by just over three degrees, with reddish Mercury visible a bit below and to the right of Venus.  As the week presses on, both planets inch a bit higher into deeper twilight, and Mercury fades from a bright -1 magnitude to zero magnitude.  However, his proximity to the extremely bright Venus means that he should be easy to spot every night about half an hour to an hour after sunset.

Mars crosses the meridian at around 9:00 pm EDT.  The planet has faded considerably since his opposition back in January, but he still holds a prominent spot near the Twin Stars of Gemini, Castor and Pollux.  His reddish tint stands out well in a sparse field of stars, especially when you compare him to the blue tint of Regulus to the east.  Mars’ apparent diameter is shrinking rapidly, and only owners of moderate-sized telescopes are attempting to view him now.

Fortunately, Saturn is now in prime viewing position for owners of smaller instruments.  The view of Saturn almost never disappoints, since his rings are visible with very modest optical aid.  The rings are tipped nearly edge-on right now as spring is slowly advancing on Saturn, but they still present a mysterious sight in the eyepiece.  Increasing aperture brings out more detail in the planet’s sphere, and more of his small icy moons also pop into view.  A 12-inch telescope at a dark location may reveal up to eight of these attendants.  Before 1980 only 10 moons were known to orbit the ringed giant.  Today there are 62 recognized satellites circling the planet!