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The Sky This Week, 2012 January 17 - 24

Giants in the sky, and counting stars for science!

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How many stars can you see in Orion?
Report your count to "Globe At Night"!


The Moon wanes through her crescent phases in the pre-dawn sky this week, with New Moon occurring on the 23rd at 2:39 am Eastern Standard Time. Luna dives down to the southern reaches of the Ecliptic, where she will mingle with the first rising stars of the summer sky. On the morning of the 19th look just three degrees below the Moon to spot the ruddy star Antares in the constellation of Scorpius. You’ll find them in the southeastern sky at the beginning of morning twilight.

The star Antares bears a striking resemblance to the star Betelgeuse in the constellation Orion, and with good reason. Both luminaries are so-called "red-supergiant" stars which have reached the end of their evolutionary tracks. Such stars have exhausted the nuclear fuel in their cores and fuse elements in nested shells surrounding their centers. As a result their outer layers balloon do diameters of hundreds of millions of miles, all the while cooling to a dull red glow. Antares and Betelgeuse are the two most prominent member of this class of stars, and by a quirk of mythological fate are among the brightest stars in their respective constellations whose figures are sworn enemies of each other. It was a lowly scorpion which dispatched the boastful Orion, who claimed dominion over all earthy animals. The two were placed in the sky on opposite sides in such a way that they would never occupy the heavens at the same time. To this day Antares rises when Betelgeuse sets, and vice-versa.

This week is the first of four opportunities you’ll have in early 2012 to do some "citizen science". From now until the night of the 23rd you’re invited to count stars and report your findings to the international "Globe At Night" campaign. The concept is simple: find the constellation Orion, count how many stars you see in the Hunter’s vicinity, visit the GAN website, and report your results using their online comparison charts. If you have a "smart phone" they even have an app you can use to make your report right from the field. The organization hopes to collect 15,000 observations worldwide, and they will use these data to determine the extent of light pollution on the global night sky. It only takes a moment of your time, and you can submit multiple reports based on weather and different locations you may encounter. If you miss this week there will be other campaigns in February, March, and April so you’ll have plenty of chances to contribute.

Skywatchers living under the brightest of urban skies should have no trouble spotting bright Venus in the evening twilight. The dazzling planet is high in the southwest at sunset, and keen-eyed observers on a clear day should be able to spot her well before sunset. Venus now sets about an hour and a half after the end of evening twilight, so folks who live in dark-sky locations should start looking for faint shadows cast by the planet’s glow.

Jupiter pops into view shortly after Venus, straddling the meridian as the Sun sets. Old Jove reaches "quadrature", the point where he is 90 degrees east of Old Sol, on the 22nd. At this time his shadow and phase angle are at their farthest extent west of the planet, which causes some interesting eclipse phenomena with the moons Europa and Ganymede. You still have several hours in the early evening to enjoy viewing Jupiter in the small telescope, but time is beginning to run out on the current apparition.

Mars now rises under the tail of Leo at around 9:30 pm EST. The red planet continues to brighten as he moves toward opposition in early March. Modest telescopes should be able to easily show the planet’s bright north polar icecap, and by the week’s end his most prominent albedo feature, the Syrtis Major, should be on the disc’s central meridian at around midnight EST.

Saturn is now well-placed for viewing during the gathering morning twilight. The ringed planet rises shortly after midnight and sits on the meridian at dawn. The planet’s rings are now tipped about 18 degrees to our line of sight, offering a good glimpse of some of their finer details. A good 4-inch telescope should reveal the Cassini Division, a gap in the rings slightly smaller than the diameter of Mars.

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