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The Sky This Week, 2017 November 21 - 28

Enjoy the waxing Moon and the Horn of Plenty.
Crescent Moon, imaged on 2017 FEB 3
with the U.S. Naval Observatory's 30.5-cm (12-inch) f/15
Alvan Clark/George Saegmüller refractor
and Canon EOS Rebel T2i DSLR.

The Moon waxes in the evening sky this week, gradually obscuring the faint autumnal constellations.  First Quarter occurs on the 26th at 12:03 pm Eastern Standard Time.  The timing is perfect for enjoying views of Luna’s surface over the holiday weekend.  After all, there’s only so much football that we can watch, and looking at the Moon is a great distraction from the struggles on the gridiron.  Luna treads a lonely path this week, with no bright objects to visit as she courses through the faint stars of Capricornus, Aquarius, and Pisces.

While most of the autumn constellations will get washed out by the light of the waxing Moon, there are a few which are bright enough to shine through the brightening sky.  The most prominent of these is a large square-shaped asterism that crosses the meridian between 8:00 and 9:00 pm.  Known as the “Great Square”, this star pattern consists of second-magnitude stars that make up a part of the mythical flying horse called Pegasus.  You’ll be hard-pressed to envision a horse from this group, especially since in classical representations half of him is missing and he’s upside down, but he is related in mythology to several other patterns that grace this part of the sky.  Go to the upper-left star in the square and look for two diverging chains of stars.  These represent the chains that bound the beautiful Andromeda to a rock for sacrifice as a result of the vanity of her mother Cassiopeia.  The latter figure is a W-shaped group that’s high in the northeast.  You’re supposed to imagine a queen on a throne admiring herself in a mirror in the five second-magnitude stars in this group!  The brighter chain of Andromeda’s stars point to the rising Perseus, who is the hero that eventually rescues the chained maiden.  All of these constellations play roles in one of the great legends of ancient times, and they still tell the same tale every clear fall night.

If you’re out near midnight after the big feast the eastern sky begins to light up with winter’s bright stars.  After the relatively sparse star patterns of autumn they are a welcome sight to accompany the lengthening nights.  By midnight the parade of first-magnitude stars known as the Great Winter Circle has cleared the eastern horizon, anchored by the striking figure of Orion, the Hunter.  The highest of the stars in the circle is now approaching the meridian in the form of a bright yellow-tinted luminary known as Capella.  The sixth-brightest star in all of the sky, Capella represents the she-goat Amalthea who suckled the infant Zeus.  The strong toddler accidentally broke off one of the goat’s horns, which then was transformed into the Cornucopia, the “Horn of Plenty” that provided its owner with whatever he or she desired.  This star and its associated legend have come to symbolize the bounty that we now celebrate as Thanksgiving.

It’s time to bid a fond farewell to Saturn for 2017.  The ringed planet now sets at the end of evening twilight, so any chance you have of spotting him in the southwest will be thwarted by the Sun’s afterglow.  We’ll now have to wait for Venus to emerge in the evening sky next spring.

After Saturn sets we have to wait until 3:30 am for Mars to rise to see the next naked-eye planet.  The red planet spends the week closing ranks with the bright star Spica in Virgo.  By the end of the week the two objects are about three degrees apart.  They provide a very nice color contrast as morning twilight begins to brighten the sky.

Jupiter rises at around 5:00 am and should be easily visible in morning twilight.  He will be the next target for Mars to set his sights on, and the two planets will steadily converge toward the end of the year.

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