The Sky This Week, March 24 – 31, 2015 !

The Sky This Week, 2015 March 24 – 31

A sure sign of spring.
The Moon & Venus, through the clouds
2015 March 22, Alexandria, Virginia

The Moon waxes in the evening sky this week, passing through the heart of the Great Winter Circle before joining the springtime constellations.  First Quarter occurs on the 27th at 3:43 am Eastern Daylight Time.  Luna passes through the Hyades star cluster and approaches the bright star Aldebaran on the evening of the 24th.  Look for bright Jupiter to the northeast of the gibbous Moon on the 29th.  She finishes the week in the company of Regulus, brightest star in the constellation of Leo, the Lion.

This is a great week to examine our only natural satellite with a telescope.  The days before and after First Quarter phase reveal a wide array of interesting lunar landscapes and formations.  You’ll soon find that the southern region of the Moon is packed shoulder-to-shoulder with hundreds of impact craters, stark evidence of the violence that led to the formation of the planets four and a half billion years ago.  The northern half of the Moon shows more of the smooth-floored so-called lunar “seas”.  These vast lava plains formed after the impacts of large asteroids early in the Moon’s long history; the enormous craters formed by these cataclysms filled with molten rock from the Moon’s interior, then were randomly peppered by random impacts from other small planetessimals.  The Moon presents a stunning view in the smallest of telescopes, but each increase in aperture will reveal more and more fine-structure detail…to a point.  Earth’s turbulent atmosphere ultimately limits the size of the smallest details you can resolve.  The best I’ve ever been able to see with our vintage 12-inch refractor here at the USNO are features on the order of a kilometer across.  That’s about the size of Meteor Crater not far from our Flagstaff Station in Arizona!

While the daffodils and tulips are struggling to let us know that spring is really here, I’ve been noticing a sure sign in the sky each night over the past week.  Rising at the end of evening twilight, the bright star Arcturus is now well up in the east at around 10:00 pm EDT.  Arcturus leads the somewhat obscure constellation of Boötes, the Herdsman and is easily found by following the “arc” formed by the “handle” of the Big Dipper.  The constellation resembles an ice cream cone with Arcturus marking the tip of the cone.  Its rosy tint tells us that it is a star in the later stages of its evolution, and its brightness indicates that it is relatively nearby.  At just under 37 light-years distance, it is the closest star of its type to the solar system.  Arcturus is the brightest star in the northern hemisphere of the sky and is fourth brightest overall.  Get used to seeing it as the nights (hopefully) become warmer.

Dazzling Venus is now catching the eyes of even the most casual skywatchers.  Her bright glow is impossible to miss in the western sky as twilight deepens to night.  She is moving through the stars of Aries, the Ram and is drawing a bead on the Pleiades star cluster, which she’ll pass around April 10th.  Venus now sets at around 10:30 pm, so you’ll have a couple of hours to enjoy her glimmer.

Jupiter crosses the meridian at around 10:00 pm, so you’ll have him in ideal viewing position for all of the evening hours.  The giant planet is still slowly creeping westward against the stars, but he’s approaching the second stationary point of the current apparition.  A modest telescope will reveal good detail in the planet’s cloud belts, which parallel the equator.  Jupiter’s most famous feature, the Great Red Spot, borders the Southern Equatorial Belt.  It will be best seen this week on the evening of the 26th, crossing the central meridian at around 9:30 pm EDT.

Saturn still greets early risers from his perch among the stars of Scorpius.  He now rises at around midnight, but you’ll have to wait a few hours to see him due to his southerly declination.  Give him a quick look now just before sunrise; it will be a great preview for the nights you’ll be watching him this summer.


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