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The Sky This Week
U.S. Naval Observatory's Weekly Blog
Falling Stars and Mad Dogs...It Must Be August!
by Geoff Chester, USNO Public Affairs
02 August 2022
Orion and Sirius rising over the Catalina Mountains, 2019 January 14
imaged from Catalina, AZ with a Canon EOS Rebel SL2 DSLR
The Moon waxes as she cruises through the southern reaches of the ecliptic, coursing her way through the heart of summer’s signature constellations. First Quarter occurs on the 5th at 7:07 am Eastern Daylight Time. Luna passes three degrees north of the bright blue-tinted star Spica on the evening of the 3rd. On the 6th her growing gibbous passes through the stars that form the “head” of Scorpius a few degrees west of the Scorpion’s ruddy heart, Antares. As the week ends she moves through the “Teapot” asterism formed by the brighter stars of Sagittarius, the Archer.
Many people associate August with the annual Perseid meteor shower, which is usually the most consistent of the annual displays of “shooting stars”. The shower typically peaks around the 12th and 13th, when a single observer at a dark-sky location may see between 50 to 100 meteors per hour. Unfortunately, this year the shower’s peak will be washed out by the Full Moon, whose bright light will be above the horizon throughout the best meteor observing hours. However, the shower is active for several days before and after the peak, so you can try spotting them almost any clear morning this week. The shower’s radiant point lies in the constellation of Perseus, the Hero, which rises above the northeastern sky by around 10:00 pm. The best time to look for early Perseids is between 3:00 and 5:00 am local time. The waxing Moon will have set by then, and the radiant will be high in the northeastern sky. By the mornings of the 8th and 9th the shower should reach a quarter to half of its peak strength, so you should be able to spot several before morning twilight interferes. The meteors are the dusty residue of Periodic Comet Swift-Tuttle, which orbits the Sun with a 133-year period. One of its co-discoverers, Horace P. Tuttle, would go on to work as an astronomer at the U.S. Naval Observatory in the latter part of the 19th Century.
Another astronomical association with August are the so-called “Dog Days”, which typically bring the summer’s hottest weather to Northern Hemisphere locations. The term originates with a phenomenon that was first widely observed by the ancient Egyptians over 5,000 years ago. They noticed that when the bright star they called Sopdet, known to us today as Sirius, rose just before the Sun the annual life-giving flood of the Nile valley soon followed. This phenomenon, called a “heliacal rising”, became the benchmark for their agricultural calendar and continued to foretell the inundation for the entirety of their long history. The personification of Sopdet was a goddess with the bright star over her head. When Egypt was conquered by Alexander the Great, Sopdet became Sothis in the Greek pantheon and was subsequently identified as Sirius, the brightest star in the constellation of Canis Major, the Greater Dog. The name “Sirius” derives from the Greek word for “scorcher”, and to the Romans its heliacal rise corresponded to the hottest days of the year. These days became known to them as the Dies Canicularis, or “Dog Days”. As Rudyard Kipling once wrote, “Only mad dogs and Englishmen go out in the midday Sun” during the “Dog Days”!
Evening skywatchers can finally welcome a bright planet to their skies as Saturn trudges resolutely toward opposition on the 14th. This week you will find the golden glow of the ringed planet low in the southeast as evening twilight ends. He is located among the dim stars of the constellation Capricornus, and by 11:00 pm he is well-placed for viewing with a telescope. His dazzling rings are tilted about 14 degrees to our view.
Bright Jupiter rises shortly before 11:00 pm, so he’s still best seen during the morning hours, but by the end of the month he’ll join Saturn for evening perusal. Early risers can see Old Jove situated between Saturn to the west and ruddy Mars to the east. Look for the bright glow of Venus in the gathering morning twilight.
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