The Sky This Week, 2012 November 27 - December 4

Jupiter, with Io and the Great Red Spot Imaged 2012 NOV 23, 03:43 UT

The Moon starts the week high among the stars of the Great Winter Circle, then presses eastward into the rising stars of spring. She wanes from the Full phase to Last Quarter, which occurs on December 6th at 10:31 am Eastern Standard Time. Look for Luna less than two degrees southeast of the bright planet Jupiter on the night of the 28th. On the following night she passes less than a degree south of Zeta Tauri, the star that marks the southern "horn" of Taurus, the Bull. By the end of the week she rises shortly before midnight among the dim stars that comprise cancer, the Crab.

The bright Moon limits the view of the sky’s fainter splendors this week, but the long winter nights are punctuated by a bevy of bright stars that not only penetrate the bright moonlight, they also overcome the light pollution that pervades the skies over our major urban areas. We’re approaching the time of the year when we experience the longest nights here in the northern hemisphere, and by a strange quirk of fate Mother Nature has seen fit to populate this part of the heavens with a bevy of bright objects. This year these bright stars are led into the sky by the bright glow of the planet Jupiter, who seems to herald the arrival of some of the sky’s most-recognized patterns.

By 9:00 pm the distinctive outline of the constellation Orion is well clear of the eastern horizon, easily visible above a typical city skyline. Most of the stars that comprise Orion all share a common origin and lie at a similar distance. If you examine the constellation with binoculars you’ll notice their icy-blue colors, with the exception of one bright star which marks one of the Hunter’s shoulders. This "outlier" is the star that goes by the name of Betelgeuse, one of the most unusual stars visible to the naked eye. Betelgeuse is a highly-evolved "red supergiant" star located some 650 light-years from the Earth. It is near the end of its lifetime, having exhausted the hydrogen in its core; this has caused its girth to swell to enormous proportions. If Betelgeuse occupied the Sun’s place in our solar system its outer layers would engulf all the inner planets out to the orbit of Mars! Since its surface is so large its surface temperature is comparatively low, with most of its radiation emitted in the infrared part of the spectrum. To our eyes it glows with a distinctive red tint, which is enhanced by contrast with the other bright stars of the constellation. In Greek mythology Orion is connected to another constellation with a distinctive reddish star. According to legend the Hunter, who was a mere mortal (albeit a very big and strong one) boasted that he held dominion over all the creatures on the Earth, a claim which upset Diana, goddess of the hunt. To put Orion’s ego in its proper place Diana sent a scorpion to challenge the boastful giant; the scorpion stung Orion in the heel as he tried to squash it with his foot. To her dismay Diana realized that she had a "crush" on the now-defunct Hunter, so she placed both victims in the sky in such a way that they would never be seen at the same time. The scorpion is, of course, the constellation Scorpius, and its brightest star is the red supergiant star Antares.

Speaking of Antares, the red planet Mars passed this star in evening twilight several weeks ago. The star has now vanished into the solar glare, but plucky Mars may still be spotted low in the southwest as twilight fades into night. This week he passes above several of the brighter stars of the constellation Sagittarius. These stars form the "handle" of the asterism commonly called the "Teapot". Act quickly if you want to see them since they disappear by 6:30 pm.

Far and away the dominant star-like object in the sky is Jupiter, which reaches opposition on December 3rd. On this night Old Jove rises at sunset and sets at sunrise, culminating near midnight high in the southern half of the sky. The giant planet is closest to the Earth on December 1st, and we’ll have to wait until the year 2021 to see him this close again. However, Jupiter’s vast size means that he always presents a generous disc for telescopic examination, so any time he’s in the sky he’s worth a look. Small telescopes will easily show his prominent equatorial cloud bands and four bright Galilean moons, but instruments of six or more inches aperture will begin to bring out a wealth of detail in his turbulent cloud tops on nights of steady air. I have been known to spend hours at the eyepiece of my 8-inch scope enjoying the constantly changing aspects of this amazing world.

The pre-dawn sky features three planets for you perusal. You’ll have no trouble finding brilliant Venus, and early in the week she’s cozying up to the more subdued glow of Saturn. By the week’s end Venus will lie almost exactly halfway between Saturn and the reddish glimmer of Mercury, which reaches his greatest elongation west of the Sun on December 4th. If you have a clear view of the eastern horizon, this will be a planetary show worth getting up on a chilly morning for!