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The Sky This Week, 2018 October 9 - 16

So long, Venus!
NGC
NGC 869 & 884, the "Double Cluster", imaged 2018 October 7
from Mollusk, Virginia with a 4-inch f/6.6 refractor telescope
and a Canon EOS Rebel T2i DSLR.

The Moon returns to the evening sky this week, sticking close to the southern horizon as she grows from a slender crescent to the First Quarter phase, which will occur on the 16th at 2:02 pm Eastern Daylight Time.  Luna may be found just three degrees north of Jupiter during the twilight hours of the 11th.  On the evening of the 14th you’ll find her less than two degrees northwest of Saturn, and she rounds out the week approaching ruddy Mars.

During the first few evenings of the week you can still get a good view of the Milky Way during the evening hours.  Evening twilight now ends shortly after 8:00 pm EDT, and by 9:00 pm the pale glow of our Galaxy’s star clouds bisect the sky from southwest to northeast.  At this time you’ll find the Summer Triangle high overhead as the stars of early summer start to set.  The Milky Way seems to split into two distinct streams in the middle of the Triangle.  This “Great Rift” is a characteristic of spiral galaxies, and there are many examples of this structure that we can see in images of edge-on spirals throughout the cosmos.  The rift is actually a vast cloud of cool interstellar gas and dust that blocks the light of more distant stars in the Milky Way’s plane.  Sweeping the Milky way with binoculars of small telescopes will reveal other deeper pockets of darkness interspersed among the galactic star clouds.  The great 19th Century American astronomer Edwin Emerson Barnard cataloged 370 of these seeming dark “voids” throughout the Milky Way.  As with the dark material in the Great Rift, these areas are not “holes” in the star clouds.  They are actually dense clouds of dark material that will eventually give birth to clusters of bright energetic stars.  You’ll find these clusters throughout the Milky Way, and many of them can be resolved with very modest optical aid.  Some of the best examples may be found in the later evening hours between the bright star Altair, southernmost star of the Summer Triangle, and Capella, one of the first bright stars of the winter sky, which may be found rising in the northeast at around 11:00 pm.  My favorite place to explore with my small refractor telescope is the area around the small “W”-shaped constellation of Cassiopeia.  You’ll find several bright clusters within the constellation’s bounds, and just northeast you’ll find the two spectacular objects known as the Double Cluster.  From a dark location the pair are easily visible to the naked eye as a bright knot in the Milky Way, and binoculars will reveal their stellar nature.  My favorite view of the pair is through my 4-inch refractor at about 36 magnifications.  The clusters fill the field with hundreds of blue-tinted pinpoints of light, with a scattering of a few orange-tinted stars.  The latter are classified as “red supergiant” stars and are among the most luminous stars known in the universe.  At their distance of around 7500 light-years from us, they shine with the equivalent light of over 250,000 Suns!

We now bid a fond farewell to Venus and her bright glow in the evening sky.  If you have an exceptionally clear night and a flat southwestern horizon you might still be able to catch a glimpse of her just after sunset for the first few evenings of the week, but by the 16th she sets with the Sun.  By the end of the month she will seem to vault into the pre-dawn sky where she’ll spend the rest of the year.

Jupiter gets a visit from the young crescent Moon on the evening of the 11th, which should help you spot him in twilight.  By the week’s end he sets before twilight ends, and in another month he, too will be lost in the Sun’s glare.

Saturn lingers in the southwestern sky as darkness falls, and you still have a little time to catch a glimpse of him in the telescope before he sinks into the horizon turbulence.  It’s worth the effort, especially if you’ve never seen the planet before.  Few things in nature elicit the “oohs” and “aahs” of first-time stargazers who catch their first look at the ringed planet.

Mars is tracking eastward through the stars of the faint constellation of Capricornus.  The red planet is doing his best to keep pace with the advancing Sun, and because of this he seems to linger near the meridian when twilight ends.  Even though he’s almost two full magnitudes fainter than he was at opposition, his location in a sky full of much fainter stars make him stand out.  Owners of modest telescopes can still catch glimpses of details on his distant dusty surface.

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