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The Sky This Week, 2015 December 1 - 8

Maidens in chains, flying horses, and a hero with a secret weapon.
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Jupiter & Io, imaged 2015 NOV 27, 11:35 UT

This week we find the Moon waning in the pre-dawn sky, wending her way through the rising stars of spring and the bright planets that may be found among them. Last Quarter occurs on the 3rd at 2:40 am Eastern Standard Time. Luna may be found three degrees south of the bright star Regulus on the morning of the 2nd. On the 4th she shares the limelight with bright Jupiter. On the 6th you’ll find the Moon just over four degrees east of ruddy Mars. The finale of this display falls on the morning of the 7th, when the Moon is situated just two degrees east of brilliant Venus. All of these mornings should offer fine photo opportunities for budding astrophotographers.

This week we enter the month-long sequence of sunrise and sunset phenomena that are associated with the Winter Solstice. From now until the 12th we’ll experience the earliest sunsets for the year at mid-northern latitudes. Here in Washington sunset will occur at 4:46 pm EST. After the 12th we begin to get a little of the evening back; by Christmas sunset will occur five minutes later, and by the month’s end the difference will be 10 minutes.

The early evening still hosts the last of summer’s stars with the Summer Triangle hanging above the western horizon. Vega, Deneb, and Altair steadily move lower as the night passes, while to the east the bright stars of the Great Winter Circle make their appearance. In between, few bright stars dominate the sky along the meridian, with the notable exception of yet another geometric figure crossing the mid-point of the sky. The "Great Square" of Pegasus is made up of four second-magnitude stars and dominates an otherwise barren stretch of the heavens. Pegasus represents the famed winged horse from the ancient legend of Perseus and Andromeda, both of whom are located nearby. Andromeda actually shares the northwest corner star of the Square, Alpheratz. You can see two diverging "chains" of stars trending eastward from Alpheratz, one made up of second-magnitude stars and the other composed of fainter third-and fourth-magnitude stars. These represent the chains that bound the beautiful Andromeda to a rock as a punishment for her mother Cassiopeia’s vanity. If you follow the bright chain of stars from Alpheratz you’ll find that it points to the star Mirfak, the brightest star in the constellation of Perseus, the Hero. Perseus resembles a large wishbone to my eye and hosts a number of bright star clusters for owners of binoculars or small telescopes. It’s most famous object is the star that is normally its second-brightest luminary, Algol. This star is the prototype of an "eclipsing binary" variable star. Over the course of just under three days the star’s apparent brightness drops by over a full magnitude and then brightens back to normal, with each eclipse lasting about 10 hours. This "winking" was thought by the ancients to represent the eye of the severed head of the Gorgon Medusa, slain by Perseus in an earlier adventure. In the Andromeda myth Perseus rides to the maiden’s rescue on Pegasus, using the Medusa’s winking eye to turn her tormentor, Cetus the sea-monster, to stone.

It’s well worth your while to rise before the Sun this week as the Moon glides through the bevy of morning planets. Each morning will bring a different configuration for your enjoyment. It is also a great time to get a telescopic view of Jupiter, who is high in the southeast at 6:00 am. The morning sky is usually when we find the least amount of turbulence in Earth’s atmosphere so it’s a great time to look for fine detail on Old Jove’s banded surface. You might also want to catch glimpses of ruddy Mars and dazzling Venus before the Sun crests the horizon.

If you live near a place with a clear view of the eastern horizon and a relatively dark sky, try to track down Comet C/2013 US10 (Catalina). This week it hangs below Venus about 20 degrees above the horizon at around 6:00 am. By the end of the week the comet will be less than five degrees from the dazzling planet and glowing at around 4th-magnitude.

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