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The Sky This Week, 2015 September 1 - 8

Spend the last weekend of summer touring the Galaxy.
Summertime Milky Way in the Summer Triangle
Imaged 2015 August 19 with a Canon EOS Rebel T2i DSLR, 24mm @f/5.6, 90 seconds
@ ISO 3200 at Fishers Island, New York

The Moon moves into the morning sky this week, climbing from the autumnal constellations to join the rising winter constellations. Last Quarter occurs on the 5th at 5:54 am Eastern Daylight Time. If you’re up before the Sun look for the Moon close to the reddish tint of the bright star Aldebaran. On the following morning Luna stands above the rising figure of Orion, the Hunter. On the morning of the 7th the Moon passes one degree north of the 2nd-magnitude star Alhena in the constellation Gemini.

As the Moon drifts into the morning sky evening skywatchers can begin to enjoy the best of the summertime sky, just in time for the long holiday weekend. If you’re venturing away from the city to the mountains or the shore, take some time in the evening to look for the fuzzy glow of the Milky Way, our home galaxy. Few urban dwellers are aware of this softly glowing ribbon of light, which bisects the sky at around 10:00 pm, so it’s a treat to be able to find a place to enjoy it. The brightest parts of the Milky Way lie to the south, just west of the "teapot" asterism of Sagittarius. When we look in this direction we are viewing the densest portions of the galaxy, gazing toward its massive core. We can’t actually see the galactic center since it is obscured by vast clouds of dust and gas as well as billions of intervening stars. If you point a pair of binoculars or a small telescope in this direction you’ll see some of these vast star-clouds as well as concentrated smudges of light betraying the presence of star clusters and glowing gaseous nebulae. Following the Milky Way toward the zenith will take you to the bright stars of the Summer Triangle, where you’ll notice a dark "rift" in the Milky Way. This dark patch is actually a vast cloud of cold interstellar gas and dust that’s blocking the light of more distant star clouds. From very dark locations you can trace out a number of intricate features in these dark regions. They were so prominent in pre-Colombian skies that the Inca and related native tribes made constellations out of them instead of the bright stars! Here again binoculars and small telescopes will show bright knots of star clusters, many of which have faint background haze from dimly glowing gas clouds. Continuing to the northeast, you’ll see the "W"-shaped constellation of Cassiopeia, whose Milky Way star clouds are littered with star clusters, including the famous "Double Cluster", one of the best binocular targets in the heavens. Take some time over the weekend to examine some of these sights. On the cosmic scale they are practically in our back yard.

Most of the bright objects you’ll see in the evening sky are stars. High in the west as twilight ends you’ll find the rosy glow of the star Arcturus, the brightest star in the northern hemisphere of the sky. Overhead you’ll find the blue-hued stars of the Summer Triangle, Vega, Deneb, and Altair. Rising in the southeast is the solitary star Fomalhaut, the most isolated of the first-magnitude stars.

The only bright planet left in the evening sky is Saturn, which glows with a yellowish tint in the southwest as evening twilight fades. The ringed planet is still a good target for the small telescope, but his time in the sky is brief, though, since he sets at around 11:00 pm. Just over 10 degrees to the east is the bright ruddy star Antares, the heart of Scorpius, the Scorpion. Saturn will spend next summer in the company of this star.

173 years ago this week President John Tyler signed S.285, the bill that established the first permanent Depot of Charts and Instruments, which ultimately became the U.S. Naval Observatory. The bill appropriated an initial sum of $10,000 for the purchase of instruments and books to establish our Library. A later appropriation of $15,000 provided for buildings and staff to operate the newly purchased instruments. By 1845 we were off and running, and we haven’t looked back since!

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