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The Sky This Week, 2019 September 24 - October 1

The stories the stars can tell
NGC 869 & 884, the Perseus Double Cluster, imaged 2018 October 7 from Mollusk, Virginia.
NGC 869 & 884, the Perseus Double Cluster, imaged 2018 October 7 from Mollusk, Virginia
with a 102 mm (4-inch) f/6.5 Explore Scientific refractor and a Canon EOS Rebel SL2 DSLR.

The Moon frames the weekend with her waning and waxing crescent phases this week.  New Moon occurs on the 27th at 11:38 pm Eastern Daylight Time.  She has been a striking sight in the pre-dawn sky for the past several days, greeting me each morning when I go out to retrieve the morning paper.  Look for the Moon’s crescent close to the bright star Regulus before sunrise on the morning of the 26th.  

The first full week of autumn presents another opportunity to enjoy cool crisp evenings under the stars while doing a bit of “citizen science” on the side.  The Globe at Night program’s monthly observing campaign once again features the constellation of Cygnus, the Swan for its September target.  Cygnus should be readily identifiable since it passes directly overhead at around 9:00 pm EDT.  Its brightest star is Deneb, easternmost and faintest of the three bright stars than comprise the Summer Triangle asterism.  Deneb marks the Swan’s tail, and his long neck terminates in the third-magnitude star Albireo, which lies about halfway between Vega and Altair, the Triangle’s other bright stars.  Between Deneb and Albireo are three stars that lie perpendicular to the Deneb-Albireo line, forming a large cross-shaped figure that makes an acceptable stick-figure Swan.  This pattern should be visible from most suburban skies, but the view from a dark location is truly breathtaking.  Fainter stars trace out the gentle sweep of Cygnus’ wings, and the soft glow of the Milky Way directs the Swan’s path to the south.  The figure of the Swan reflects the Greco-Roman mythology that dominates the constellations as we know them today, but other cultures see the same patterns in different ways.  One of my favorite bits of sky lore for this constellation comes to us from the Inuit people of the arctic regions.  They see a man in a kayak paddling his craft along the “Pebbly River” of the Milky Way.  Whatever figure you choose to see, take some time this week to find Cygnus and compare your view with charts on the Globe at Night website.  Give your eyes some time to adapt to the darkness, and try to observe from a spot that’s not in the direct illumination from streetlights.  Your observations will help scientists track the spread of light pollution, which is gradually robbing us of our night skies as well as causing disruption to the circadian rhythms of nocturnal animals, birds, and even humans.

By midnight the Summer Triangle occupies the western sky while another geometric figure begins to cross the meridian.  This figure forms an almost perfect square of second-magnitude stars and marks the body of Pegasus, the mythical winged horse of Greek mythology.   Pegasus is one of several related constellations that grace the autumnal sky.  Draw a northward line through the stars on the left side of the square to find the “W”-shaped constellation of Cassiopeia, the Queen.  According to the Greeks, she was a very vain queen, constantly admiring herself in a mirror.  One day she claimed that her beauty surpassed that of the Sea Nymphs, the consorts of Poseidon, god of the oceans.  Poseidon decided to punish the queen by chaining her daughter Andromeda to a rock to be devoured by a fearsome sea monster.  You can see Andromeda’s chains diverging from the upper left corner of the square, marked by the star Alpheratz.  Fortunately, the hero Perseus arrives on Pegasus, kills the monster, and saves the vain queen’s daughter!  Perseus lies just to the northeast of Cassiopeia and is anchored by the bright star Mirfak.  To me the constellation resembles the part of a broken wishbone that the “winner” gets.  The area between Perseus and Cassiopeia is one of the best parts of the sky to scan with binoculars or small telescopes.  The bright star Mirfak is surrounded by a scattered group of fourth- and fifth-magnitude stars that form a loose galactic star cluster known as Melotte 20.  It is located about 560 light-years away.  Buried in the Milky Way between Cassiopeia and Perseus is one of my favorite objects in the entire sky, the “Double Cluster”.  Visible as a pair of fuzzy knots of light in binoculars, its true splendor is revealed in small telescopes of 3- to 4-inch aperture.  View it from a dark site for a truly spectacular experience.

Jupiter continues to hold court in the early evening sky, appearing in the southwest as twilight falls.  Despite his far southerly declination Old Jove remains the brightest object in the evening sky until he sets at around 10:30 pm.  If you want to get a decent view of him in the telescope point your instrument at him as soon as you can see him in twilight.  Atmospheric turbulence will degrade the clarity of his image as he heads toward the southwest horizon.

Saturn crosses the meridian shortly after sunset, and should become visible in deep twilight by 8:00 pm.  The ringed planet is best observed before 10:30 pm, when he, too, will follow Jupiter toward the southwest horizon.  He sets at around midnight, leaving the sky bereft of bright planets for the rest of the night.

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