The Sky This Week, 2012 October 2 - 9
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The Great Andromeda Galaxy, Messier 31 |
The Moon wanes in the morning sky this week, passing high over the stars of the Great Winter Circle that now grace the early morning hours. Last Quarter occurs on the 8th at 3:33 am Eastern Daylight Time. Look for the Pleiades star cluster five degrees to the north of the Moon on the morning of the 4th. Luna will straddle Jupiter before dawn on the 5th and 6th.
As the Moon moves into the morning sky it’s time to take advantage of the crisp, clear nights of early autumn. This is my favorite time of the year for observing. The nights are cool but not biting, the hazes of summer are replaced by clear air, and some of the best sights for the telescope are available in the rapidly-lengthening nights. Summer’s constellations are still available for perusal as evening twilight fades, with the bright stars of the Summer Triangle hanging overhead as the last of dusk’s stray light fades. Many amateur astronomers like to seek out specific targets among the star clusters and nebulae that dominate this part of the sky, but quite often I like to simply sweep the sky with a small telescope at low power and see what wafts through the eyepiece. Once something catches my eye I’ll try to identify it on my star charts. At these magnifications many of the familiar Messier objects are little more than fuzzy blobs, but quite often they seem like tiny jewels set in backgrounds of endless star clouds. The small scope offers a wonderful window onto some of the larger features of our Milky Way galaxy that can often be overlooked when one is peering at a specific cluster or nebula with a larger instrument. In addition to the galaxy’s star clouds, keep an eye out for seemingly empty voids. These "holes in space" are in reality vast cold clouds of non-luminous gas that obscure the light of background stars as well as stars that are incubating within. Eventually some of these dark clouds will burst to light as newly-formed star clusters to entertain our distant descendents!
By midnight the scene shifts to a more subdued sky. The Summer Triangle now hangs lower in the west, and now the most prominent stars are mostly second and third-magnitude luminaries of the autumnal constellations. High in the south you should be able to easily find a large square-shaped asterism that forms part of the constellation of Pegasus, the Flying Horse. This part of the sky takes our distant gaze away from the plane of the Milky Way and directs it to deep space. Large amateur telescopes reveal countless small fuzzy wisps of light, the signatures of far-flung external galaxies. However, a simple pair of binoculars or just your unaided eyes at a good dark site can spy one of these galaxies quite easily. Start by locating the Great Square of Pegasus and go to the upper-left corner star, Alpheratz. You’ll see two diverging chains of stars that trend to the northeast. Follow the lower, brighter chain out to the second star, then hop "up" over two fainter stars. You’ll see a faint, elongated swatch of light that resembles a detached portion of the Milky Way. This is the Andromeda galaxy, the closest large galaxy to us in the cosmos. It is the combined light of some 400 billion stars and is generally said to be the most distant object you can see without a telescope. It is a treat for any kind of optical aid whether you’re using binoculars or an observatory-class telescope. Its light stubbornly refuses to resolve into pinpoints of stars, and its texture is unique among the brighter deep-sky objects. In my 80mm (3-inch) refractor I can trace its outer arms out nearly two degrees on either side of its nucleus. In time the view will only get better. Andromeda is approaching us at a velocity of about 120 kilometers per second (80 miles/sec), and in just under 4 billion years will collide with the Milky Way!
Much closer to home, Mars continues to pace the Sun in his eastward trek around the Zodiac. This week you’ll find him approaching the stars that form the "head" of Scorpius. By the end of the week he approaches the second-magnitude star Dschubba. He’ll pass a degree north of the star on the 10th.
Jupiter now rises just before 10:00 pm, and he’ll make steady progress into the evening sky during October. By Halloween he’ll rise about two hours earlier as he prepares to assume his place as king of the night. Of all the planets Jupiter is the most satisfying for the small telescope owner. His disc subtends a generous size which will reveal a substantial amount of detail in instruments of a very modest aperture, while the four bright moons first observed by Galileo shuttle back and forth around their giant master.
With sunrise in Washington now occurring after 7:00 am EDT many of us are being dazzled by the bright glimmer of Venus in the east as we gather the morning paper or walk the family dog. The planet shines at a blazing magnitude of -4.1, which is bright enough to cast shadows in very dark locations. You won’t see your shadow by the light of Venus this week since the Moon gives her fierce competition, but later this month you can try to spot this elusive sight.
