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The Sky This Week, 2020 July 7 - 14

Thunder Moon, begone!
Jupiter & the Milky Way, imaged 2019 July 5 from Mollusk, Virginia.
Jupiter & the Milky Way, imaged 2019 July 5 from Mollusk, Virginia
with a Canon EOS Rebel SL2 DSLR, 18mm @ f/4, 20 second exposure at ISO 6400, unguided.

The Moon wanes in the late night and early morning skies this week as she climbs northward along the ecliptic into the rising autumnal constellations.  Last Quarter occurs on the 12th at 7:29 pm Eastern Daylight Time.  Look for the Moon near ruddy Mars if you’re up before the Sun on the mornings of the 11th and 12th.

If you find yourself at a location with a flat eastern horizon try your hand at looking for a rare visitor to our skies.  Comet C/2020 F3 NEOWISE has been delighting early risers for the past several days as it drifts above the northeast horizon in the gathering twilight.  It is proving to be a fine sight in binoculars, and observers in dark, open locations have reported it to be visible with the naked eye.  The comet was discovered on March 27, 2020 by the Wide-field Infrared Survey Explorer (WISE), a space-based observatory launched in 2009 to map the sky at infrared wavelengths.  When its supply of liquid helium, used to cool its sensitive detector, ran out in 2011 the spacecraft was put into hibernation.  However, astronomers realized that the satellite could still do useful work, so it was re-activated in 2013 and renamed NEOWISE.  Sine that time the spacecraft has discovered thousands of asteroids and about three dozen comets.  This one passed close to the Sun on July 3rd and is now outbound from the inner solar system.  It should remain visible about 10 degrees above the northeast horizon at around 5:00 am local time for another week or two before it fades below naked eye brightness.

With the Moon’s exit from the evening sky we can once again enjoy another fixture of the seasonal sky, the summer Milky Way.  From a dark location this softly glowing band resembles a faint luminous cloud arcing from the northeast to the southern horizon.  At 11:00 pm local time you can see the densest part of the band just to the east of the bright stars of Scorpius, the Scorpion, which hovers over the south skyline.  The Milky Way is our home galaxy, and from our perch about 30,000 light-years from its center we can see its densest star clouds.  The center itself is invisible at visual light wavelengths, obscured by vast alternating clouds of stars and dark interstellar dust, but you can locate its approximate position by noting the thickest part of the bulge of star clouds near Scorpius.  The vast clouds are bisected by irregular dark patches of cool dust and gas, and from a dark site a small wide-field telescope will reveal intricate detail in the dark voids.  Interspersed among the star clouds are glowing knots of light, the signs of bright star clusters and glowing clouds of nebulosity from which those clusters formed.  Small low-power telescopes of three- to four-inch aperture are ideal for revealing these features as well as the vast swarms of faint stars that make up the galaxy’s glowing bands.

High up in the east as midnight approaches are the three bright stars that delineate the Summer Triangle asterism.  This is another wonderful area to poke around with a small telescope.  The bright stars Vega, Deneb, and Altair gleam bluish-white in color, contrasting nicely with the colors of the star Albireo, which sits almost at the triangle’s center.  Point your telescope at this star and you will be rewarded with a beautiful double star with contrasting colors of blue and gold.  I like to think of Albireo as “the Navy Double” every time I look at it.  

Jupiter and Saturn are both set to command the night’s center stage.  The two gas giants are both nearing opposition, when they are above the horizon all night long.  Jupiter is unmistakable as the brightest object in the sky after the Moon and Venus, and despite his low declination his glow powers through much of the summertime haze and humidity so typical of July skies.  Any telescope will show the giant planet’s four Galilean moons.  It’s fun to follow them as they shuttle back and forth around their hulking master.

Saturn follows Jupiter, and while he’s not as bright, he still should be easy to spot.  Saturn’s main attraction are the tenuous rings, which are still tipped at around 20 degrees to our line of sight.  On moments when the air is steady look for the gap towards the outer edge of the rings.  This gap, known as Cassini’s Division, is some 4500 kilometers (3000 miles) wide, about the distance from the eastern tip of Maine to San Francisco.

Mars gets a visit from the Moon over the weekend.  These events are still best seen in the pre-dawn sky when Mars hangs like a glowing coal over the eastern horizon.  The red planet is now a good target for owners of modest-sized telescopes.  His disc resembles a fat gibbous Moon, and his bright south polar cap should be easy to spot.

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