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The Sky This Week, 2016 November 22 - 29

A cornucopia of celestial morsels
NGC 869 & NGC 884, the Perseus Double Cluster
Imaged from Fishers Island, NY on 2013 April 15
with an Antares Sentinel 80mm (3.1-inch) f/6 refractor
and a Canon EOS Rebel T2i DSLR

The Moon greets early risers as a waning crescent in the pre-dawn sky this week. New Moon occurs on the 29th at 7:18 am Eastern Standard Time. Look for the Moon near bright Jupiter on the mornings of the 24th and 25th.

The absence of the Moon finds us in the middle of the November observing campaign for the international "Globe at Night" campaign. This global "citizen science" effort is dedicated to determining the effects of light pollution around the world, and it is very simple for anyone to participate. This month the effort focuses on the constellation of Perseus, the Hero, which may be found high in the northeastern sky at around 9:00 pm. If you face north at his time you’ll see the "W"-shaped constellation of Cassiopeia on the meridian; she’ll actually look a bit more like an "M". Perseus occupies the space just to the right of Cassiopeia and is centered on the second-magnitude star Mirfak. I think of Perseus as resembling the "winner’s" portion of a wishbone, which seems quite appropriate for this time of year. The top of the wishbone points back toward Cassiopeia while the longer tine follows a gentle arc that will lead you to the Pleiades star cluster. The shorter, upper tine ends in a most unusual star, Algol. Its name derives from ancient Persian and means "the head of the demon", and it represents an eye on the severed head of the Gorgon Medusa that Perseus dispatched in one of his many adventures. The star is unusual in that its apparent brightness dims by over one magnitude every 2.87 days, as if it was slowly winking at us. This was noticed by the classical Arab astronomers in the first millennium, who thus gave it a very descriptive name. The reason for this unusual behavior is that Algol is an "eclipsing binary" star, in which a dim companion star periodically blocks the light from the brighter component. The next minima of Algol occur on the 26th at 10:44 pm and on the 29th at 7:33 pm EST. You should have little trouble in finding Mirfak and Algol from suburban skies, although Algol may be difficult when it is at a minimum. To make a measurement for Globe at Night, compare your view to the online charts on the project’s website and add your data to the growing knowledge base.

Just below Perseus you’ll find a bright star that has a very distinctive golden tint. This is Capella, the brightest star in the constellation of Auriga the Charioteer. Capella’s name is derived from the Latin word for "goat", and it represents Amalthea, the she-goat who nursed the infant Zeus as he was hidden from his father Cronus. In one legend the young Zeus accidentally broke off one of the goat’s horns which then became the source of boundless nourishment, the Cornucopia. Fittingly in our modern traditions Capella is close to the meridian at midnight when we take the time to celebrate the bounty and nourishment in our lives with the Thanksgiving feast.

Venus is trekking through the stars of Sagittarius, starting the week near the constellation’s brightest star Nunki. She is now beginning to move northward along the ecliptic, and sets well over an hour after the end of evening twilight.

Mars spends the week crossing through the heart of the dim autumn constellation of Capricornus. You’ll find him in the early evening sky in the southwestern sky, a solitary ruddy beacon in an otherwise bland star field. He keeps a steady pace against the advancing Sun and sets at the same time, 9:48 pm, each night this week.

Jupiter is very well placed for early rising skywatchers, high in the east as morning twilight begins to lighten the horizon. He gets a visit from the Moon on the 24th and 25th, and on the latter morning there will be a fine grouping of Luna, Old Jove, and the first-magnitude star Spica.


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