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The Sky This Week, 2015 April 7 - 14

Tracking down a hairy tale.
Jupiter & Io, imaged 2015 April 5, 02:27 UT

The Moon wanes in the morning sky this week, skirting the southern horizon as she passes through the signature constellations of summer.  Last Quarter occurs on the 11th at 11:44 pm Eastern Daylight Time.  Look for Luna close to golden Saturn among the stars of the head of Scorpius on the morning of the 8th.  On the 10th and 11th she passes over the “teapot” asterism in Sagittarius before drifting eastward into the fainter stars of the autumnal sky.

As we mentioned last week, April is Global Astronomy Month, a program sponsored by Astronomers Without Borders.  Starting on the evening of the 9th, the April session of the Globe at Night begins, lasting until the return of the waxing Moon on the 18th.  This month the featured constellation for northern hemisphere observers is Leo, the Lion.  While not as prominent as Orion in terms of bright stars, Leo is nevertheless quite easy to find and identify thanks to the nearby presence of bright Jupiter.  Leo crosses the meridian at around 10:30 local daylight time and can be distinguished by two asterisms.  Closest to Jupiter is a “backwards question mark” consisting of the first-magnitude star Regulus, the second-magnitude star Algieba, and four other third-magnitude stars which together form the Lion’s “head”.  Eastward of this group is a right triangle made up of second-magnitude Denebola (“The Lion’s Tail”), and the third-magnitude stars Zosma and Chort.  From my light-polluted suburban yard I can just make out all of these principal stars.  How many can you see from your site?  Count them and report them here!

As the Moon retreats into the morning sky we have our last chance to say goodbye to the stars of winter.  At 9:00 pm, just as evening twilight ends, you can still see all of the stars in the Great Winter Circle surrounding the central figure of Orion.  One by one the bright stars set during the course of the evening, with Orion taking his bows at around 11:30 pm.  You’ll have about an hour or so after the end of twilight to explore the rich starfields of the Milky Way to the east or Orion before the region gets too close to the horizon.  By midnight the dominant “deep-sky” objects become distant external galaxies, many of which can be found in modest telescopes sprinkled among the stars of Leo, adjacent Virgo, and the faint constellation Coma Berenices.  This latter star pattern is almost impossible to see from urban site, but is quite prominent when seen from a good dark place.  Consisting of a scattering of 4th- and 5th-magnitude stars, it is an actual star cluster located some 250 light years from the Sun, once of the closest of its kind to us.  It is named in honor of Queen Berenice II, wife of King Ptolemy III of Egypt, who cut off her “golden tresses” as a sacrifice to ensure her husband’s safe return from battle.  When the offering disappeared from the temple, the court astronomer Conon pointed the star cluster out to the royal couple and convinced them that the queen’s hair had been transferred into the sky.

Venus continues to move eastward against the stars, and you can easily watch her progress this week as she glides just to the south of the Pleiades star cluster.  She is just under three degrees from the Seven Sisters on her closest approach on the evening of the 11th.  You will have no trouble finding Venus as she dominates the western twilight sky, but you may want to use binoculars to get a good look at the Pleiades.  They are among the best sights for this type of optical aid, and you should see many more stars than the seven attributed to it by the ancients.

Jupiter now crosses the meridian at around the end of evening twilight.  This is the best time to get a good look at him, but he’s still well-placed for viewing until around midnight.  Nights of steady air will reveal a wealth of detail on the giant planet’s face, and careful scrutiny will show subtle changes over the course of an hour or so as the planet’s fast rotation constantly brings new features into view.  Look for the planet’s famous Great Red Spot at around 9:00 pm on the evening of the 7th and 10:30 pm on the evening of the 9th.  The moon Io drags its shadow across Old Jove’s face between 9:30 and 11:00 pm on the 11th.

Even though Saturn now rises before midnight, his southerly declination doesn’t allow him to clear the trees and horizon haze until the wee hours of the morning.  The best time to observe him is still in the hours before sunrise.  Morning twilight now begins at around 5:30 am, so he’s now well-placed for early risers.  He receives a visit from the Moon before dawn on the 8th, and spends the rest of the week among the second-magnitude stars in the “head” of Scorpius.



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