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The Sky This Week, 2020 August 18 - 25

A cosmic chase that never ends.
Scorpius and the summer Milky Way, imaged from Mollusk, Virginia, 2020 July 26.
Scorpius and the summer Milky Wa7
imaged from Mollusk, Virginia, 2020 July 26

The Moon returns to the evening sky this week, waxing through her crescent phases to First Quarter, which occurs on the 25th at 1:58 pm Eastern Daylight Time.  As she dives southward along the ecliptic, you will find her just over five degrees north of the bright star Spica on the evening of the 22nd.  She ends the week among the stars that form the “head” of Scorpius, the Scorpion.

For those of you who like stargazing in the evening sky, you may have noticed that sunset here in the Washington area now occurs before 8:00 pm.  That’s about 40 minutes earlier than the time of sunset at the summer solstice.  This means that for many of us in urban and suburban locations we can enjoy dark (ish) skies at around 9:00 pm.  If you’re in a darker location the sky is fully dark by around 9:30 pm.  We are currently losing about 2.5 minutes of daylight per day, so it’s becoming easier to enjoy your summer favorites and still get to bed at a decent hour.

Speaking of Scorpius, you will find this signature summer constellation crossing the meridian at 9:00 pm local time.  While it is placed in the southernmost reaches of our Washington skyline it is still one of the showpieces of the sky.  If you can find a spot to see it in all of its splendor you won’t need a lot of imagination to understand how it got its name.  Scorpius is a very ancient constellation, depicted in records of ancient Egypt and Mesopotamia that date back well over 5000 years.  It is led by a prominent red-hued star known as Antares, which translates as “rival of Mars”.  Antares is a red supergiant star, a highly evolved example of a star that is nearing the final stages of its life.  Like its counterpart Betelgeuse in Orion, Antares is vast, with a girth that spans hundreds of millions of kilometers.  If Antares occupied our Sun’s place in the solar system, the orbit of Mars would be inside of it!  Scorpius shares some other details with Orion as well.  Many of its stars are hot blue giant stars that share a common origin, much like the bright blue stars in Orion.  While the two constellations share similar physical characteristics, their mythology is also linked, but in an unusual way: you will never see the two in the sky together at the same time.  

Our Greco-Roman skylore tradition paints Orion as a boastful hunter who claimed that he could kill all the animals on Earth.  His pride and arrogance didn’t sit well with Gaia, goddess of the Earth, so she sent a scorpion to teach the hunter a lesson.  The scorpion’s powerful sting dispatched Orion, but he was saved “in the nick of time” by Ophiuchus, the Serpent-bearer, whose large constellation appears above Scorpius in our summer sky.  To appease both parties Zeus placed both Orion and the scorpion in the sky, but opposite each other so that they would never have to face off again.

Early in the week you can still see the bright stars-clouds of the Milky Way from dark-sky locations.  They rise up from the vicinity of Scorpius and arc overhead through the bright stars of the Summer Triangle.  Mild summer evenings make them particularly attractive to scan with binoculars or small telescopes.  The sheer number of stars that you can see is mind-boggling.  Also note the dark, seemingly empty regions of the Milky Way’s band.  These are clouds of non-luminous gas and dust that feed the formation of stars along the Galaxy’s plane.

Jupiter now shines brightly in the southeastern sky as soon as evening twilight starts to fall.  Old Jove is now in prime viewing position for evening stargazers, offering a variety of sights for the small telescope owner.  His constantly shifting bright moons and changing atmosphere can be studied with telescopes of four-inch aperture or larger.  On the evening of the 23rd you can watch his innermost moon Io drag its shadow across the planet’s disc, and on the following evening you can get a fine glimpse of the famous Great Red Spot rotating across his face.

Saturn should be your next stop after Jupiter.  I have been looking at this planet for decades through dozens of different telescopes and I still get a chill when I view it.  There is something about the view of Saturn that defines “other-worldly” and keeps me at the eyepiece.  One glimpse for yourself and I think you’ll see why.

Ruddy Mars waits in the wings, now rising at around 10:30 pm.  That’s still a bit late for me, but with later times of sunrise it’s now not unreasonable to take a look at the red planet in morning twilight.  He is steadily brightening and his visible disc is steadily growing as we near opposition, set for early October.

Venus accompanies Orion and the other rising winter constellations as morning twilight brightens the sky.  You should have no trouble spotting her beaming down from the stars of Gemini.