The Sky This Week, 2012 October 23 - 30
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Clearing sky, waxing Moon, 2012 October 19 |
The Moon continues to brighten the evening sky as she moves eastward and northward along the Ecliptic through the dim stars of the autumn constellations. Full Moon occurs on the 29th at 3:49 pm Eastern Daylight Time. She courses a lonely path this week, with no bright companions to call upon until she encounters Aldebaran and Jupiter next week. October’s Full Moon is known as the Hunter’s Moon, with similar orbital geometry to last month’s Harvest Moon. Just as the Harvest Moon provides a little extra light to help farmers bring in their crops, the Hunter’s Moon gives hunters a little extra light to pursue game across the stubble of the harvested fields. The difference between times of successive moonrise around the time of Full Moon is about half an hour here in Washington, and it becomes less at higher latitudes. For comparison on most nights Luna rises about an hour later.
The bright moonlight washes out all but the brightest stars in this week’s sky. In some ways this is a good thing, since it accentuates the simpler patterns of bright asterisms that are sometimes lost in a sea of fainter stars. The easiest stars to locate are the bright stars of the Summer Triangle, which may be found high overhead just west of the meridian in the early evening. Vega, Deneb, and Altair each lead their own separate constellations, but many of their companions are lost in the bright wash of Moon glow. It’s much easier to recognize the bright stars and their simple geometric figure under these conditions. By 10:00 pm the triangle has settled farther west, and a square-shaped group approaches the meridian. This figure isn’t as prominent as the triangle, being composed of second-magnitude stars, but it shouldn’t be too challenging even under the brightness of the Full Moon. The "Great Square" is a part of Pegasus, the mythical flying horse from the ancient Greek tale of Perseus and Andromeda. Both Perseus and Andromeda are nearby, but perhaps the easiest character to recognize from the story is Andromeda’s mother, Queen Cassiopeia. You’ll find her to the northeast of Pegasus as a compact grouping of stars resembling the letter "W". By midnight Cassiopeia straddles the meridian and the eastern sky brightens with the rising stars of the Great Winter Circle. This asterism is very hard to miss, since nine of the 25 brightest stars in the sky may be found within its bounds.
By the end of the week we finally have two planets occupying the evening sky at the same time…for about three minutes! Ruddy Mars sets as bright Jupiter rises, but for the bulk of the evening hours neither one is particularly well-placed.
Mars continues his steady march eastward along the Ecliptic, pulling away from his rival star Antares. He spends the week passing above the back of Scorpius as he works his way toward the stars of Sagittarius. You’ll need a clear night and a low southwest horizon to see him in deepening twilight before he sets shortly after 8:00 pm.
Jupiter continues to rise earlier each night, and by the end of the week you should be able to spot him in the east by 9:00 pm. He rises along with the red-hued first-magnitude star Aldebaran and golden Capella, harbingers of the Great Winter Circle. Old Jove will reach opposition in early December, but if you find yourself up at midnight it will be worth your while to train the telescope on him
Venus continues to welcome us before dawn. In the last few days before we return to Standard Time her cheery glow is greeting many of us as we rise for the work day. Venus is also moving rapidly eastward against the stars. Just a few weeks ago she blew by Regulus in the constellation of Leo, the Lion. Leo is now quite high in the east as morning twilight gathers, a reminder that springtime isn’t all that far off in the future.
