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The Sky This Week, 2015 March 17 - 24

An equinox eclipse, and winter's hidden treasures.
Star clusters Messier 46, Messier 47, and NGC 2423 in Puppis
Imaged 2015 February 15 from Morattico, VA

The Moon returns to the evening sky by the end of the week.  New Moon occurs on the 20th at 5:36 am Eastern Daylight Time.  At this time Luna’s disc will cover the Sun in a total solar eclipse.  The path of totality runs from south of Greenland eastward, passing just south of Iceland and north of the northernmost parts of Great Britain.  Here the path begins to curve northward, passing over the Danish Faroe Islands.  It then passes over the Norwegian archipelago of Svalbard before ending at the North Pole.  The partial phases will be visible from most of Greenland, Europe, northwestern Russia and North Africa.  Luna’s slender crescent should be visible on the evening of the 21st in deepening twilight.  Use binoculars to find the planet Mars just a degree to the north of the Moon that evening.  On the following night you should have no problem locating the waxing crescent close to the bright planet Venus.  Finally, on the evening of the 24th, the Moon should present a fine binocular sight as it approaches the Hyades star cluster and the bright star Aldebaran.

For those of you who have had your fill of winter, take heart.  The Vernal Equinox occurs on the 20th at 6:45 pm EDT, signaling the beginning of the astronomical season of spring in the Northern Hemisphere.  For the next six months the Sun will move along the northern half of the ecliptic and the length of daylight will exceed that of night.  This may be a small comfort to our friends in New England, but at least the crocuses and budding daffodils that I’m seeing in my yard are sure indicators that warmer days are on the way.

Before the Moon returns to the evening sky take advantage of the departing winter constellations as evening twilight falls.  Last week we looked at the obscure constellation of Monoceros, the Unicorn.  This week we’ll look at another interesting star pattern that was once part of the largest star pattern in the sky.  This pattern lies to the east and south of the more well-defined constellation of Canis Major, the great Dog, marked by the brightest star in the sky, Sirius.  The pattern we’re looking for is called Puppis, and marks the stern of the fabled ship Argo, the vessel that bore Jason on his quest for the Golden Fleece.  Argo covered such a vast area of the sky that when astronomers began cataloging stars they ran out of Greek letters to identify them.  To fix this problem they broke Argo into 4 new constellations, of which Puppis is the only one visible from our climes.  Right now Puppis crosses the meridian in the southern sky at around 9:00 pm.  From a dark location you can see some of the brighter star-clouds of the Milky Way as they float above the south horizon.  This is prime territory for exploring with binoculars and small telescopes.  Dozens of star clusters may be found here and in the adjacent Canis Major.  Perhaps my favorites of all of these are located about 12 degrees east of dazzling Sirius.  Messier 46 and 47 should be easy to spot in binoculars as two fuzzy knots, but it doesn’t take a large telescope to see them in their full glory.  M46 is the denser cluster and will challenge resolution in a 3-inch telescope, while M47 is a somewhat more scattered group of brighter stars.  Just north of M47 is another cluster visible in a small telescope, NGC 2423.  If you have a six-inch scope, M46 will reveal a further surprise.  On its northern edge you’ll see a “star” that doesn’t seem to be in focus.  This is a so-called “planetary nebula”, the result of a star in its death throes.  Designated as NGC 2438, this is the only such nebula to be found in a star cluster.  Take the time to explore the area around these celestial gems for more hidden treasures.

Venus is now climbing higher in the twilight sky, slowly outpacing the pursuing Sun.  By the week’s end she sets almost an hour and a half after the end of evening twilight.  Venus is so bright because its dense atmosphere is perpetually shrouded with bright reflective clouds that reflect about 65 percent of the sunlight that strikes them.  If you are in a very dark location, Venus sheds enough light to cast faint shadows.  Try this for yourself over the next couple of months.

Jupiter defers to Venus in the early evening sky, but once Venus sets Old Jove becomes the brightest nighttime object after the Moon.  The giant planet is in prime viewing position starting in deep twilight and crosses the meridian at around 10:30 pm.  A modest telescope will reveal considerable detail in the planet’s turbulent cloud belts, and the four bright moons discovered by Galileo can be seen with almost any optical aid.  This week the planet’s famous Great Red Spot may be glimpsed in steady air on the evenings of the 19th and 21st.  On the former evening you can watch the moon Io cross the planet’s disc beginning at around 8:30 pm EDT.  The moon’s shadow follows beginning at 9:20 pm.  On the 21st the moon Europa transits the planet beginning at 9:30 pm.  Its shadow will follow at 11:20 pm.

Saturn is still best seen before sunrise this week.  At 6:00 am the ringed planet is just west of the meridian hob-nobbing with the stars that form the head of the constellation Scorpius.  The planet’s rings are tipped a generous 25 degrees to our line of sight, and a morning of steady air will reveal their complex structure to bleary-eyed telescopic observers.




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