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The Sky This Week, 2013 November 19 - 26

Prowling near Pegasus

Globular Cluster Messier 15 in Pegasus

Imaged at Fishers Island, NY with an 80mm (3.1-inch) f/6 Antares Sentinel refractor
and a Canon EOS Rebel T2i DSLR camera

The Moon wanes in the late evening and early morning sky this week, starting her journey among the bright stars of the Great Winter Circle before drifting into the rising stars of spring. Last Quarter occurs on the 25th at 2:28 pm Eastern Standard Time. Luna passes just over a degree south of the second-magnitude star Alhena in the constellation Gemini during the late night hours of the 20th. On the 21st she may be found some five degrees below bright Jupiter. Early risers will find her five degrees to the south of the bright star Regulus in Leo before dawn on the 25th, and she winds up the week in pursuit of ruddy Mars.

The first hours of darkness on these lengthening autumn nights still give us a good-bye glimpse of departing summer constellations. The Summer Triangle hangs impressively over the western horizon, and you can still catch a number of interesting objects in binoculars or the small telescope before Vega, Deneb, and Altair slip into the horizon haze. By 8:00 pm the fainter constellations of the autumn sky pass through the meridian, bringing views of more distant deep-sky objects interspersed among the more open star fields. At this time look for a large square made up of second-magnitude stars high in the south. This figure is a part of Pegasus, the mythical Flying Horse, which can help you find a number of often-overlooked sky treasures.

If you face south, draw an imaginary line between the two stars on the right side of the square and extend it toward the southern horizon. You’ll notice a lone, bluish star about 20 degrees above the skyline. This is Fomalhaut, the most isolated of the first-magnitude stars and the brightest luminary in the constellation of Pisces Austrinus, the Southern Fish. Fomalhaut was one of the first stars to have a debris disc imaged by the Hubble Space Telescope, and a small moving body within that disc may actually be a planet comparable to Jupiter in mass.

Return to the square and draw a line between the two stars on the left side and extend it down toward the south. You will encounter a second-magnitude star, Diphda, in the constellation of Cetus, the Whale. This star is notable for its orange tint, which contrasts nicely with Fomalhaut. If you live near a dark-sky location, sweep the sky about seven degrees south of Diphda with binoculars or a small telescope. You should run into a very elongated swath of hazy light that betrays the galaxy NGC 253. Popularly known as the Silver Dollar Galaxy, this star system is one of the closer ones to the Milky Way at a distance of about 11.4 million light-years. After the Andromeda Galaxy, NGC 253 is probably the second-easiest external galaxy for northern hemisphere observers to spot.

Finally, go back to the square and extend a line to the right (west) from the bottom two stars.  You'll run into a yellow-tinted second-magnitude star named Enif.  About four degrees further west from Enif you'll see another fuzzy, almost circular blob of light.  This is Messier 15, one of the ancient globular star clusters orbiting around the hub of the Milky Way.  A six-inch or larger telescope will begin to resolve the "fuzz" into a swarm of faint stars that blend into an amorphous haze near the center.

By now you’ve probably noticed dazzling Venus in the southwestern sky at dusk and have seen her linger into the hour after full astronomical darkness. Now that we’re on Standard Time and folks are commuting home in relative darkness Venus is attracting more and more attention. What you’re seeing now will be the norm for the next several weeks. By year’s end she will start to drop precipitously back toward the Sun.

Jupiter continues to edge his way into the evening sky. By the end of the week he rises just before 8:00 pm, and by 10:00 he’s impossible to miss in the eastern sky. Jupiter is the small telescope owner’s favorite planet, revealing his four bright moons and dark cloud belts in instruments of 3-inches aperture or better. If you’re up at 11:00 pm on the night of the 20th, give Old Jove a look. You’ll find the famous Great Red Spot near the center of the planet’s disc, trailed by the tiny black dot of the moon Io’s shadow.

Mars is still best seen just before the start of morning twilight. His ruddy glow is located just below the tail of Leo, the Lion. Mars is beginning to gain in brightness as Earth begins to catch up to him, and his disc is beginning to gain in size for owners of moderate aperture telescopes.

You’ve probably heard some "buzz" about a visitor to our part of the solar system known as Comet ISON. This object is briefly visible before dawn near the bright star Spica over the next few mornings. It is due to pass about 1.12 million kilometers (700,000 miles) above the surface of the Sun on Thanksgiving Day. If it survives this scorching encounter with Old Sol it could become visible to the naked eye in the evening sky in early December. Stay tuned!

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