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The Sky This Week
U.S. Naval Observatory's Weekly Blog
Sights for the Coming Autumn Nights
by Geoff Chester, USNO Public Affairs
30 August 2022
Summer Milky Way composite, from Sagittarius to the Summer Triangle, imaged 2022 August 22
from Thoroughfare Mountain Overlook, Mile 39, Skyline Drive, near Luray, Virginia.
Canon EOS Rebel SL2 DSLR, 18mm @ f/4, ISO 3200, 90-second exposures using an Omegon LX-2 MiniTrack mechanical star tracker.
The Moon waxes as she wends her way along the southern reaches of the ecliptic. First Quarter occurs on September 3rd at 2:08 pm Eastern Daylight Time. Look for Luna just to the west of the three stars that form the “head” of Scorpius, the Scorpion on the evening of the 2nd. On the 5th she lies within the bounds of the asterism known as the “Milk Dipper” in the constellation of Sagittarius, the Archer.
As September opens we enter the time of year when the length of daylight changes at its most rapid pace. On September 1st the length of day here in Washington is 13 hours, and by the 25th it will be just 12 hours. Each day is now about 2.5 minutes shorter than its predecessor. This is a boon to skywatchers, who don’t have to wait until the evening is half over to enjoy the starry sky, but it also means that it’s darker in the mornings when we get up for work or school. September is also the month when we begin to lose the haze and humidity of high summer, making for very pleasant evenings at the telescope eyepiece. As if to reward us for tolerating the short summer nights, September nights offer us some of the best sights in the sky.
The Labor Day weekend is usually the last opportunity to head for darker skies at the beach or in the mountains before kids return to school and the rest of us settle into our daily routines of jobs and home. If you are headed for that favorite vacation spot, take advantage of stargazing away from city lights. The waxing crescent Moon shouldn’t add too much light to the sky for the first half of the week, offering a good opportunity to see the magnificent arc of the summer Milky Way. As you follow the Galaxy’s glowing ribbon of light toward the southern horizon you are looking in the direction of the Milky Way’s center, gazing at vast star clouds and obscuring clouds of cold gas and dust. We can’t actually see the center, which is located some 30,000 light years away, due to the sheer volume of stars and dark matter that intervenes. However, if you scan the glowing band with binoculars, your eyes will be filled with innumerable stars, star clusters, glowing gaseous nebulae, and mysterious dark voids. Spend some time scanning the Milky Way from the southern horizon up through the stars of the Summer Triangle and back toward the northeast to the “W”-shaped constellation of Cassiopeia.
If you can’t get away to see the Milky Way, enjoy the colorful stars sprinkled along its path. In the south you can find the red-tinted star Antares, the “heart” of Scorpius, the Scorpion. The star’s name means “Rival of Mars”, and it is an apt descriptor. Antares is a cool red supergiant star similar to Betelgeuse in Orion. High overhead are the bright stars of the Summer Triangle asterism. Two of these stars, Vega, the brightest of the group, and Altair, the southernmost, are relatively near to us at distances of 25 and 16.7 light years, respectively. Deneb, the faintest of the three, is actually 100 times farther away from us than Vega, which means that it must be some 200,000 times more luminous than the Sun. If Deneb was located at the distance of Altair our summer nights would be very different. Its apparent brightness would rival the first quarter Moon, and we would never see the Milky Way!
Saturn is now well established in the southeastern sky as evening twilight fades. The ringed planet is gradually drifting westward among the stars of the constellation Capricornus. He is in the same binocular field as the Sea-Goat’s brightest star, Deneb Algeidi and its widely spaced companion Nashira. Saturn crosses the meridian at local midnight, so you have a lot of time to study his dazzling rings through the telescope.
Giant Jupiter now rises shortly before 9:00 pm, and as late evening becomes early morning he climbs higher in the eastern sky. Old Jove is about one month away from opposition, but you should have no trouble finding him among the dim stars of Pisces, The Fish. With Venus all but invisible now, Jupiter is the brightest object in the sky after the Sun and Moon.
Ruddy Mars now peeks above the northeast horizon shortly before midnight, but the best time to see him is in the early morning. This week the red planet passes above the Hyades star cluster in Taurus, the Bull, and seems to give the beast a second fiery red “eye”.
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