The Sky This Week, 2012 September 4 - 11
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Messier 11, the "Wild Duck" Cluster in Scutum |
The Moon wanes in the morning sky this week, vaulting northward among autumn’s dim stars to finish among the rising stars of the Great Winter Circle in the pre-dawn twilight. Last Quarter occurs on the 8th at 9:15 am Eastern Daylight Time. Look for Luna between the Pleiades star cluster and the bright star Aldebaran in Taurus, the Bull, on the morning of the 7th. The following morning she lies just one degree south of the bright planet Jupiter, and by the week’s end her waning crescent is closing in on dazzling Venus.
By the middle of the week the Moon rises after midnight, kicking off the next good interval to explore the stars of summer and early autumn. As the days rapidly grow shorter the end of evening twilight occurs at around 9:00 pm, and at this time the three bright stars of the Summer Triangle, Vega, Deneb, and Altair straddle the meridian with Vega parked almost directly at the zenith. From a dark location it’s fairly easy to spy the wafting glow of the Milky Way coursing through the triangle and spilling southward toward the horizon. I have spent many hours sweeping through the star clouds of our home galaxy with binoculars and small telescopes, picking out some of the brighter knots and dark voids for closer inspection with larger instruments. In this part of the sky you can see many different types of objects. What look like faint knots of light in binoculars reveal themselves to be luminous clouds of gas and dust lit by the energy of hot young stars that formed in their interiors or older clusters of hundreds of luminous stars just beginning their long evolutionary tracks. Other smudges are globular star clusters containing hundreds of thousands of stars, some as old as the universe itself. Some of these "globular clusters" may be the remnants of dwarf galaxies that collided with the Milky Way eons ago and now orbit in the Galaxy’s vast halo. Then there are the dark areas, many of which are so distinct that the Inca gave them a place in their sky lore. Encountering these clouds with a telescope is almost startling; from an eyepiece field filled with uncountable faint stars you’ll suddenly encounter a field full of blackness! These "dark nebulae" are vast clouds of cold interstellar gas and dust, the stuff that may some day form other new star and planetary systems.
Our evening parade of planets that has graced the sky since the beginning of the year has by now receded into the glare of evening twilight, with one notable exception. Ruddy Mars is now keeping pace with the advancing Sun in the southwestern sky, and he’ll continue to occupy this niche of the sky through the end of the year. You won’t find very much to see through the eyepiece of even the biggest telescopes since his rosy disc is now a mere five arcseconds in apparent diameter. Fortunately we have a new set of eyes preparing to roam the red planet, so we can all follow the exploits of the Mars Science Laboratory "Curiosity" as it roams the floor and central peaks of a large martian crater.
Giant Jupiter rises just before midnight along with the first bright stars of the Great Winter Circle. This puts him in fine position to observe before sunrise for you early risers. Old Jove is a welcome sight in the telescope eyepiece with his ever-changing surface cloud belts and shuttling moons. You’ll never have the same view twice when you look at the solar system’s largest planet!
Venus rises at around 3:00 am, and by the first glimmers of morning twilight she is well up in the eastern sky. This week the dazzling planet moves from the eastern fringes of the Great Winter Circle into the dim constellation of Cancer, the Crab. If you have a pair of binoculars watch Venus close in on the "Beehive" star cluster by the end of the week. She’ll glide just south of the cluster on the morning of the 14th.
