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The Sky This Week, 2019 October 22 - 29

Sparkling stars on crisp autumn nights
The Perseus/Cassiopeia Milky Way, imaged 2019 September 28 from Blackwater Falls State Park, West Virginia.
The Perseus/Cassiopeia Milky Way
imaged with a Canon EOS Rebel SL2 DSLR from Blackwater Falls State Park, Davis WV.
Note the Perseus "Double Cluster" to upper left of center.

A waning crescent Moon graces the early morning sky this week, coursing her way through the rising springtime constellations.  New Moon occurs on the 27th at 11:38 pm Eastern Daylight Time.  Look for the bright star Regulus, heart of Leo, the Lion, southeast of the Moon before dawn on the 23rd. 

The October observing campaign for the citizen-science “Globe at Night” program continues this week.  The featured constellation of the month is Pegasus, the Winged Horse.  You’ll have to exercise a considerable amount of imagination to trace the ancients’ interpretation of Pegasus in the sky; the classical depictions show only the beast’s front half, and it is depicted upside down to boot.  Far easier is to look for a nearly perfect square of stars high in the east at 9:00 pm.  While none of the stars is brighter than second magnitude, the “Great Square” should nevertheless be easy to spot from urban skies.  From darker skies, however, more stars start to appear inside the square, providing a good indicator of local sky brightness.  Use the sample star charts on the Globe at Night website to compare your view of Pegasus and his environs and report your findings.  If you are under particularly dark skies you should be able to spot a number of stars inside the square’s boundaries.

Northeast of Pegasus lies the small but distinct constellation of Cassiopeia, the Queen.  Like Pegasus its brightest stars are second magnitude and form an asterism that resembles the letter “W”.  Cassiopeia is firmly set in a dense Milky Way star field, and it is one of my favorite parts of the sky to explore with binoculars and low-power telescopes.  There are dozens of star clusters liberally sprinkled throughout the constellation’s brighter stars that appear as small knots of fuzzy light in binoculars, and these begin to resolve as you move to telescopes of increasing aperture.  If you continue past Cassiopeia toward the northeastern horizon, you will come across the bright star Mirfak, brightest star in the constellation of Perseus, the Hero.  Mirfak is surrounded by a number of bright blue-tinted stars that, together with Mirfak, form one of the closer galactic star clusters to the solar system.  Known as Melotte 20, it is a splendid sight in binoculars.  Halfway between Mirfak and Cassiopeia your binoculars will reveal two closely-spaced knots of light, which a small telescope will resolve into two distinct clusters of dozens of stars.  These are collectively known as the Perseus Double Cluster, and they are one of the true showpieces of the night sky.  With each increase in telescope aperture more faint stars appear in each cluster, and more background Milky Way stars dot the surrounding field.  That said, I enjoy the view in my small 3-inch travel telescope just as much as I do with my 14.5-inch “light bucket”.  The pair are located some 7500 light-years away, and they contain some of the youngest stars known in the sky, having formed just over 12 million years ago.  Some of the individual stars in each cluster are highly luminous and hot, shining with a luminance some 100,000 times that of our Sun!

Venus can now be spotted in the evening twilight, low in the southwestern sky.   Look for her about half an hour after sunset south of the point on the horizon where Old Sol disappears.  Despite the brightness of the sky you should still be able to see the dazzling planet if you have a good view with a flat horizon.  She currently sets shortly after 7:00 pm, but by this time next month she will set at the end of astronomical twilight.

Jupiter lingers in the early evening sky, first appearing in twilight about 20 minutes after sunset.  He spends the next few hours settling toward the southwest horizon, where he sets at around 9:00 pm.

Saturn still offers a few hours of good viewing time before he follows Jupiter’s path toward the southwest horizon.  As evening twilight ends you will find the ringed planet below a small asterism in Sagittarius that is popularly called the “Teaspoon”.  Over the course of the next few weeks watch his slow eastward progress against this fine binocular grouping.

Finally, here is a note to my readers.  Due to a directive from our superior Command, many of USNO’s Web services will be unavailable beginning on October 24th.  We anticipate a six-month lapse in these services while our systems and software are upgraded.  The availability of “The Sky This Week” may be affected, but we are actively exploring workarounds should this be the case.  Thank you for your patience and support while we undergo this upgrade process.

 
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