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The Sky This Week, 2020 July 28 - August 4

A comet exits, bright planets enter.
Comet C/2020 F3 NEOWISE, imaged 2020 July 26, 02:51 UT from Mollusk, Virginia.
Comet C/2020 F3 NEOWISE and the Big Dipper, imaged 2020 July 26, 02:51 UT from Mollusk, Virginia
with a Canon EOS Rebel SL2 DSLR, 18mm @ f/5.6, composite of 5 90-second exposures at ISO 3200.

The Moon skirts the southern horizon this week, passing through the southerly summer constellations as she waxes to her full phase.  Full Moon occurs on August 3rd at 11:59 am Eastern Daylight Time.  August’s Full Moon seems to have more popular names than any other month’s.  It is variously known as the Corn Moon, Grain Moon, Red Moon, Dog Moon, and Sturgeon Moon.  Luna lies just over two degrees south of bright Jupiter on the evening of the 1st.  On the following night you can find her southwest of yellow-hued Saturn. 

Comet C/2020 F3 NEOWISE has been delighting skywatchers for several weeks, first as an easy naked-eye object in the pre-dawn sky and more recently at more reasonable evening hours.  Sadly it is now on its way out of the inner solar system, so it has faded below easy “eyeball” visibility except for those folks that live in extremely dark skies.  It is still visible in binoculars provided that you know where to look for it, appearing as a condensed fuzzy ball of light with a slight greenish hue.  I had a couple of very nice views of it this past weekend from Virginia’s Northern Neck using a pair of binoculars and a small spotting scope.  This week it will drift eastward through the dim constellation of Coma Berenices within the bounds of a triangle formed by the bright star Arcturus, Alkaid, the star that marks the end of the “handle” of the Big Dipper, and Denebola, the tail of Leo, the Lion.  Bright moonlight will hamper the view, but it should still be worth hunting it down from a dark-sky location.  It should continue to be visible in binoculars and small telescopes for a few more weeks.  Try to catch it now; it won’t be back to visit us again until the year 8704! 

You may have noticed that one of the names for the upcoming Full Moon is the Dog Moon.  This particular appellation derives from the ancient Roman expression “Dies Caniculares” that were used to describe the hot and sultry weather typical of late July and early August.  These “Dog Days” coincided with an astronomical phenomenon known as the heliacal rising of Sirius, the brightest star in the night sky.  During late July Sirius can be seen rising shortly before the Sun from temperate northern latitudes.  The star was known as the “Dog Star” to the ancient Greeks and Romans, leading them to associate the phenomenon with the heat of high summer.  The heliacal rise of Sirius was also noted by more ancient people.  Sometime around 3000 BCE the ancient Egyptians noticed that the annual appearance of Sirius at sunrise presaged the annual flood of the life-giving Nile.  This was probably the most important event in their annual observances, since the silt brough from the African interior in the floods rejuvenated the fields in the Nile valley, ensuring a successful agricultural bounty to feed the growing population.

Jupiter is now prominent in the southeastern sky as evening twilight fades.  He stands out as the brightest object in this part of the sky and commands attention despite the haze that pervades these sultry nights.  If you have a small telescope Old Jove will provide your best planetary target.  His apparent disc is large enough to resolve in a good 3-inch instrument, and you should be able to see his two dark equatorial cloud belts without difficulty.  Larger telescopes reveal more detail, and careful observation over an hour or so will reveal the planet’s rapid rotation rate as new features cross from west to east.  Jupiter’s most peculiar surface feature, the Great Red Spot, occasionally faces us at convenient times.  You should be able to see it easily in a four-inch telescope.  It is believed to be a persistent storm system in the planet’s atmosphere, but the nature of its striking color remains a mystery.

Saturn tags along about 10 degrees east of Jupiter.  Nearly twice as far from us as Old Jove, Saturn’s apparent diameter is half that of his larger rival.  Saturn’s atmosphere is also much more subdued; individual spots like those on Jupiter are very rare events.  However, Saturn’s real draw are its mesmerizing rings.  Almost any telescope will reveal them, but to really get a good view of them you’ll want at least four to six inches of aperture.  They are currently tipped about 20 degrees to our line of sight, and they will be gradually closing up over the next several years.  As solid as they appear through the eyepiece, they are actually very tenuous, made up of shattered remains of small moons that ventured to far into the planet’s immense gravitational field.  In a few million years the rings will disappear unless another tiny moon ventures too close.

Ruddy Mars now rises before midnight and climbs above the horizon haze by 1:00 am.  He is now wending his way through the faint stars of Pisces, but he has no bright competition in his part of the sky.  He will be entertaining a number of earthly visitors in February, 2021 as space probes from the U.S., China, and the United Arab Emirates will reach his distant shores.  The Chinese and UAE probes were launched last week; America’s “Perseverance” rover is scheduled to take off on the 30th.

Early risers should have no trouble spotting Venus in gathering morning twilight.  She is currently drifting eastward through the stars of Taurus, the Bull, and if your sky is clear enough you may see the rising of the first stars of Orion.  Is winter really that far off?

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