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Follow that Swan!

by Geoff Chester, USNO Public Affairs | 05 September 2023

by Geoff Chester, USNO Public Affairs | 05 September 2023

NGC 6888, the Crescent Nebula in Cygnus, imaged 2023 August 12 from Mollusk, Virginia
with an Explore Scientific AR102 10.2-cm (4-inch) f/6.5 refractor,
Optolong L-eNhance dual bandpass filter, and a ZWO ASI183MC CMOS color imager

The Moon wanes in the morning sky this week, arcing high along the ecliptic as she passes through the rising stars of the winter sky.  Last Quarter occurs on the 6th at 6:21 pm Eastern Daylight Time.  Early risers can see an attractive triangle formed by the Moon, the bright star Aldebaran, and the Pleiades star cluster during the pre-dawn hours of the 6th.  On the morning of the 10th Luna forms a line with the Gemini twins, Castor and Pollux, in gathering morning twilight.

The September observing campaign for the citizen-science Globe at Night program kicks off on the evening of the 5th and lasts through the 14th.  This month’s target constellation is Cygnus, the Swan, a staple for summer stargazers.  

Cygnus occupies much of the space bounded by the “Summer Triangle” asterism and passes directly overhead at around 10:00 pm local time.  Its brightest star, Deneb, is the northernmost and faintest star in the Summer Triangle, and to the ancient Greeks marked the Swan’s tail.  

In urban skies on a very transparent night you may be able to make out a cross-shaped grouping of stars that delineate the Swan’s long neck and wings.  This figure becomes much easier to see as you move farther away from bright city lights.  Under dark rural skies the Swan’s figure is very easy to see, as it seemingly flies southward along the diffuse light of the Milky Way.  

To the ancient Greeks the Swan represented Zeus in one of his many guises to promote his amorous adventures among goddesses on Mount Olympus.  To the Inuit of the arctic regions the figure represented a man in a kayak paddling along the “Pebbly River” of the Milky Way.

Once you have located Cygnus, go to the Globe at Night web app and follow the directions to make your observation.  Compare your observation with the star charts on the site, answer a few questions about your location and sky conditions, and submit your sighting.  Your information, along with that of thousands of other citizen-scientists, will help astronomers to map the overall brightness of the sky and how it is evolving.

Cygnus and the adjacent constellations offer an abundance of sights for amateur astronomers.  My favorite ways to explore these regions is with binoculars or a small, low-power telescope.  Star clusters abound in the Milky Way star clouds, along with faintly glowing patches of interstellar gas.  If you point your binoculars toward the star Sadr, which marks the intersection of the Swan’s “wings” and “body”, look for a moderately bright star just to the southwest of Sadr.  This is P Cygni, one of the most luminous stars in the galaxy.  It is a very rare type of star known as a Luminous Blue Variable (LBV), of which only a handful are known in our galaxy.  It is a star on a very short fuse that emits well over 600,000 times the energy of the Sun.  Its life span is measured in a few million years, and it will end with a spectacular supernova explosion.

Just over two degrees west of P Cygni is another unusual object known as the Crescent Nebula.  This is a softly glowing oval of gas surrounding another rare kind of object known as a Wolf-Rayet star.  These stars are very luminous and emit most of their light in the ultraviolet part of the spectrum.  This UV light stimulates gas in a surrounding “bubble” to glow, much like gas in a neon tube.

Mars continues to plod eastward along the ecliptic and is theoretically visible in twilight shortly after sunset.  You will need binoculars and a very clear sky with a view to the western horizon to glimpse him at around 8:00pm.

Saturn casts a cheery yellow glow in the southeast as evening twilight fades.  The ringed planet should be very prominent by 10:00 pm before Jupiter rises in the east to steal some of his thunder.  A small telescope will show his famous rings and his brightest moon Titan.  A good six-inch telescope will show the Cassini Division in the rings and several more moons.

Giant Jupiter rises at 10:00 pm local time as the week opens.  Old Jove is passing through the diminutive constellation of Aries, the Ram, and he will spend the majority of the current apparition there.  He dominates the eastern sky as midnight approaches and maintains a steady presence until sunrise.

Dazzling Venus greets early risers as morning twilight begins to brighten the eastern horizon.  The planet is very hard to miss as she outshines everything else in the sky after the Sun and Moon.


Commander, Naval Meteorology and Oceanography Command | 1100 Balch Blvd. | Stennis Space Center, Mississippi 39529

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