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The Sky This Week, 2016 January 12 - 19

Winter's brightest stars in prime time.
Orion, Sirius, and Aldebaran
Imaged on 2016 January 2 from Morattico, Virginia

The Moon waxes in the evening sky this week, wending her way northward along the ecliptic to join the stars of the bright winter constellations. First Quarter occurs on the 16th at 6:26 pm Eastern Standard Time. Luna passes in front of the bright star Aldebaran on the evening of the 19th. The star will disappear behind the Moon’s dark limb at 9:28 pm EST and reappear on the bright limb at 10:36 pm. The disappearance should be easily visible with the unaided eye, but you’ll probably want to use a small telescope to observe the reappearance. Residents along the northern Gulf Coast and the Florida-Georgia state line will see a spectacular "grazing" occultation where Aldebaran will seem to "flicker" as it passes behind lunar peaks and valleys along Luna’s southern limb.

As the Moon waxes she brightens the evening sky, gradually obscuring most of the fainter stars of the autumnal constellations that grace the western half of the celestial sphere in the early evening. Fortunately, these stars soon set, and by 9:00 pm the bright stars of the Great Winter Circle take over as they approach the meridian. The circle is centered on Orion, The Hunter, perhaps the single most recognized constellation in the sky. Orion is visible from every inhabited part of the planet, and virtually every civilization that has left us records of their sky lore has a name for this prominent group. An imaginary line drawn through the Hunter’s three bright "Belt" stars points southeastward to Sirius, the brightest star in the sky. Moving clockwise from Sirius the circle passes through the stars Procyon, Pollux, Castor, Capella, and Aldebaran before winding up at Rigel, one of Orion’s blue "kneecaps". Near the center of the circle is the star Betelgeuse, one of the most colorful stars in the sky. The star’s warm orange tint contrasts with the cooler ice-blue hues of Rigel and the constellation’s other bright stars. The star’s unusual name is a corruption of its Arabic name, Ibt-al-Jauzah, which, loosely translated, means "The Armpit of the Central One".

The confines of the Great Winter Circle contain many of the sky’s brightest stars, which makes it a welcome sight for those of us in the Northern Hemisphere who face long nights during our winter season. Most of these stars are relatively close to us on the cosmic scale. Sirius lies a mere 8.5 light-years away from us, while Procyon is just 11 light-years away. The most distant of the Winter Circle’s stars is Aldebaran at 67 light years, but then we get to Rigel. This star, the 7th brightest in the entire sky, is nearly 1000 light-years away! This means that Rigel must be an immensely bright star with a luminosity some 60,000 times greater than our Sun’s! If we could somehow throw a giant lasso around Rigel and drag it to the nearby distance of Sirius it would shine with the apparent brightness of the first-quarter Moon. Our winter nights would be very different in that case!

The planets are now beginning to span more of the night. Leading off is giant Jupiter, which now rises at around 10:00 pm. He’s nestled under the hindquarters of Leo, the Lion, one of the signature constellations of the coming spring. The best time to view him is in the wee hours of the morning, but he’s high in the southwest in the hours before sunrise. Through the telescope you can enjoy the antics of his four bright moons, first documented by Galileo 405 years ago this month. On the morning of the 15th three of them will seem to clump together to the west of the planet.

Mars continues to drift eastward toward the star Zubenelgenubi in Libra, a pale ruddy beacon in the southeastern pre-dawn sky. Its small pink disc is gradually beginning to grow in size as Earth begins to catch up to the red planet, but you’ll still be hard-pressed to see much detail other than its bright north polar cap.

Saturn is next up, having been passed by Venus last week. You should be able to see his wide-open rings before he gets washed out by encroaching twilight.

Finally, bright Venus crests the southeast horizon as the sky brightens before sunrise. It should be visible up to the time of sunrise, a dazzling beacon in the pale blue light of dawn.

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