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The Sky This Week, 2015 November 3 - 10

Some basic geometry in the night sky.
Messier 31, the Great Andromeda Galaxy
Imaged 2015 August 8 with a Canon EOS Rebel T2i DSLR, 80mm f/6 Antares Sentinel refractor,
20 90-second subframes @ ISO 3200 at Fishers Island, New York

The Moon wanes in the morning sky this week, passing through the gathering of planets in the pre-dawn hours. New Moon occurs on the 11th at 12:47 pm Eastern Standard Time. Look for Luna just over two degrees from bright Jupiter before sunrise on the 6th. The next morning the Moon provides an excellent photo opportunity with brilliant Venus and the more subdued ruddy Mars. The three objects will form a tight triangle spanning just over two degrees. In the middle of this triangle you’ll find the third-magnitude star Zavijah.

Late autumn nights are characterized by large geometric asterisms that dominate different times of the nighttime hours. The early evening is marked by the lingering stars of the Summer Triangle, Vega, Deneb, and Altair, hanging high in the western sky. From dark-sky locations this group of bright blue-white stars is pierced by the wafting glow of some of the brighter star-clouds of the Milky Way. There are a number of interesting objects to look at here if you have a small telescope. The star Albireo lies in the center of the triangle and resolves into a fine pair of blue and golden-hued stars in almost any telescope. Near the bright star Vega a pair of binoculars will reveal a close pair of white stars. Looking at this wide pair of stars with a three-inch or larger aperture telescope shows that each component is itself a close double star.

By 9:00 pm another geometric figure may be found crossing the meridian high in the south. This is the so-called "Great Square" of Pegasus. Even though none of the square’s stars are brighter than second-magnitude, they are the brightest stars in this part of the sky. You can get a good idea of the quality of your sky by counting the faint stars inside the square. Urban skywatchers will be lucky to see one or two, but those well away from city lights may be able to see up to a dozen! If you look at the upper left star in the square, Alpheratz, you’ll see two diverging "chains" of stars; follow the lower, brighter chain to the second star, then hop up past the second star in the fainter chain. From a dark site you’ll see a fuzzy patch of light with your unaided eye, and even from the city binoculars will show a glowing luminous patch. This is the Great Andromeda Galaxy, the closest large external galaxy too the Milky Way. It represents the combined light of some 200 million stars and lies at a distance of 2.5 million light years!

By midnight our last geometric figure is climbing in the east. The Great Winter Circle surrounds the familiar outline of Orion, the Hunter, and here you’ll find nine of the 25 brightest and most colorful stars in the sky. This is another area that’s a treat to look at in binoculars.

Early risers will find the Great Winter Circle sliding past the meridian as the stars of the springtime sky move into the east. This is where you can see the season’s bright planets. Jupiter is the highest of the three worlds in this part of the sky. Venus is the brightest of the three, and you’ll find the dazzling planet pulling away from the much fainter glow of Mars. For added drama, the Moon glides through these assembled worlds for what will be one of the best astro-photo opportunities of the year.

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