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The Sky This Week, 2019 October 15 - 22

Summer stars on autumn nights.
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NGC457, the 'Owl Cluster' in Cassiopeia, imaged 2019 September 27 from Blackwater Falls State Park, West Virginia.
NGC457, the 'Owl Cluster' in Cassiopeia
imaged with an Explore Scientific 10.2-cm (4-inch) f/6.5 refractor
and a Canon EOS Rebel SL2 DSLR from Blackwater falls State Park, Davis WV.

The Moon moves into the late night and early morning skies this week, waning to Last Quarter on the 21st at 8:39 am Eastern Daylight Time.  Luna eases into the rising winter constellations, passing through the heart of the Great Winter Circle for early risers to enjoy.  Look for the Moon between the Pleiades and Hyades star clusters before daybreak on the 17th.  

As the week progresses the Moon rises later each successive evening.  This allows more time in the evening hours to enjoy the spectacle of the late summer Milky Way.  These early fall evenings are my favorites for viewing the many interesting sights in our home Galaxy.  There’s no more summer haze and humidity, the mosquitoes are gone, and the conditions aren’t too frigid for an evening’s stargazing session.  Astronomical twilight now ends at around 8:00 pm EDT, so there are several hours of darkness for a galactic tour before the Moon comes up.  From a dark location, the Milky Way runs from the southwest to the northeast, with the bright stars of the Summer Triangle asterism high overhead.  The brightest part of the Milky Way stretches from the Triangle toward the southwest horizon, where you can still see the “Teapot” asterism of Sagittarius.  The center of the Galaxy lies just above the Teapot’s “spout”, so when we look in this direction we are looking through clouds of countless stars.  A good pair of binoculars will start to reveal the nature of these clouds, and as you sweep back up toward the Summer Triangle you will see a number of luminous knots that betray the presence of bright star clusters and star-forming regions called “nebulae”.  My favorite instrument for exploring this region is a relatively small 4-inch refractor telescope that I use with a low-power eyepiece.  Many of these fuzzy knots resolve into stars with this instrument, and the star clouds themselves begin to show their stellar nature, interspersed with dark voids that indicate the presence of dark clouds of cold gas and dust.  These “dark nebulae” obscure the light of more distant stars, but eventually they will begin forming their own stars, evolving into more star clusters for future skywatchers to enjoy.  Continue sweeping along the Milky Way to the northeast and you will continue to see star clusters embedded in the soft background of the Milky Way.  By the later evening the W-shaped constellation of Cassiopeia is high in the northeast, and this is one of the best areas of the sky to look for star clusters.  The small telescope will reveal dozens of clusters of varying size, brightness, and star density.  One of my favorites can be found by drawing a line from the left-most star in the “W” through its nearest neighbor to the southwest.  Extend that line to the next bright star and you will run into NGC457, popularly known as the “Owl Cluster”.  Once you get the cluster in the eyepiece you will see why it gets its name.  Two bright stars mark the owl’s “eyes”, and the scattered fainter stars give a god resemblance to the owl’s body with outstretched wings.

Toward the end of the week look just east of the meridian at around 10:00 pm for a well-defined square-shaped asterism.  This distinctive pattern is known as the Great Square, and it outlines part of the body of Pegasus, the legendary Flying Horse of Greek mythology.  This pattern will be the focus of the October campaign of the Globe at Night citizen-science program, which runs from the 19th to the 28th.  The Great Square has long been used as a gauge of sky darkness, since the number of stars that can be seen within its bounds increases as sky brightness decreases.  Most of us in cities and suburbs won’t see any stars inside the Square, but travel well away from city lights and the asterism starts to fill with fainter luminaries.  I was able to spot ten stars inside the Square on a recent trip to Blackwater Falls in West Virginia.

It’s time to start looking for Venus in the bright glow of early evening twilight.  Half an hour after sunset look just above the southwest horizon for the planet’s bright glimmer.  She will gradually increase her distance above the horizon over the next few weeks, then she will vault into the evening sky as November turns to December.

Jupiter is also prominent in the deepening twilight, visible in the southwest as the sky darkens.  The giant planet quickly descends toward the horizon over the next couple of hours, setting before 9:30 pm.

Saturn follows Jupiter in the southwestern sky, but lags behind Old Jove by about an hour and a half.  He thus still spends a fair amount of time in a dark sky, so you still have a good “window” of time to view him before he settles into the turbulence above the horizon.  As twilight ends you will find the ringed planet just east of the “Teapot” of Sagittarius.