The Sky This Week, April 21 – 28, 2015 !

The Sky This Week, 2015 April 21 – 28

It’s spring! Get out and gaze!
Jupiter & Io, 2015 April 13

The Moon returns to the evening sky this week, making a final pass through the departing stars of winter before joining the stars of spring.  First Quarter occurs on the 25th at 7:55 pm Eastern Daylight Time.  Luna forms an attractive triangle with the bright star Aldebaran and dazzling Venus on the evening of the 21st.  On the 23rd she slides by the second-magnitude star Alhena in the constellation Gemini.  On the 25th and 26th you’ll find the Moon close to giant Jupiter. Finally, on the 27th, the Moon lies just four degrees south of the first-magnitude star Regulus.


This is a great week to take up some of the lunar observing challenges offered as a part of Global Astronomy Month.  Getting to know one’s way around our only natural satellite is one of the best ways to become involved in amateur astronomy.  Whether you have binoculars, a small telescope, or a behemoth Dobsonian reflector there’s something for everyone to discover among the mountains, plains, and craters of the lunar surface.  Use the online finder charts and guide to track down the Moon’s most interesting formations as the terminator line slowly reveals more of Luna’s disc on successive nights.  On the 24th, join others for lunar exploration via the Virtual Telescope Project and explore the moon through your Web browser.  And on the evening of the 25th, find your local amateur astronomy club and join in on the Global Star Party as astronomers around the world celebrate “One people, one sky”.  Here in the Washington, DC area you can join members of the Northern Virginia Astronomy Club for a public viewing session at C.M. Crockett Park in Fauquier County, or venture out to Paris, Virginia to join other amateur astronomers at Sky Meadows State Parkfor the first of this year’s series of star parties.


As the trees bloom and the air grows milder the last of winter’s constellations make their last stand.  Evening twilight now ends at around 9:30 pm, and the bright stars of Orion and Canis Major only have an hour or so to shine before they slip below the southwestern horizon.  In the meantime, two signature constellations of spring now straddle the meridian.  High in the south you’ll find Leo, the Lion, just east of the bright glow of Jupiter.  Leo’s brightest star, Regulus, marks the Lion’s heart, while an arc of second- and third-magnitude stars curves off to the north, delineating the Lion’s head.  To the east of this asterism, popularly known as the “sickle”, is a right triangle representing the big cat’s haunches.  The star at the eastern tip of the triangle is called Denebola, which translates to “The Lion’s Tail”.  Now turn to face north and you’ll see the familiar stars of the Big Dipper, although they will appear upside-down as if water is pouring from the dipper’s bowl.  These seven stars form part of the much larger constellation of Ursa Major, the Great Bear.  Five of the seven stars in the dipper form a physical association, moving through space together, and it is thought that our Sun may be a part of this sparse, far-flung star cluster.


Venus continues to move eastward, gradually gaining altitude above the western horizon.  This week she closes in on the star Al Nath, the northern “horn” of Taurus, the Bull.  She stays in the sky for a couple of hours after sunset, shining her bright glow until well after 11:00 pm.


Jupiter now crosses the meridian as the Sun sets, and begins his journey toward the western horizon as darkness falls.  You’ve still got a few hours to enjoy the view of the giant planet in a telescope, but his disc is gradually shrinking as Earth leaves him in its wake.  Despite the enormous distance between our worlds, Old Jove still presents us with the largest apparent disc of any of the planets, and on nights of steady air you can still glimpse tantalizing views of his distant cloud tops.  On the evening of the 21st his largest moon Ganymede crosses the planet’s face, looking like a large black spot against the brilliant equatorial zone.  At the same time the famous Great Red Spot rotates into view.  You’ll get another good view of this jovian storm on the 26th.  If you’re observing Jupiter during the Global Star Party on the 25th, all four Galilean moons will be string like beads to the west of the planet at 9:00 pm.


By the end of the week Saturn rises in the southeastern sky at around 10:00 pm.  The ringed planet is located in the bright stars of the head of Scorpius, the Scorpion, one of the signature constellations of summer evenings.  Saturn’s rings are now tipped generously toward our line of sight and can be detected in steadily-held binoculars, but use a telescope if you can to get their full spectacular effect.


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