Each Monday I pick out the northern hemisphere’s celestial highlights (mid-northern latitudes) for the week ahead, but be sure to check my main feed for more in-depth articles on stargazing, astronomy and eclipses. 

What To Watch For In The Night Sky This Week: August 17-23, 2020

This week is all about the absence—and then the dramatic and delicate reappearance—of the Moon. Its absence from the night sky is a boon for stargazing, making it much easier to see deep sky sights such as star clusters, galaxies and nebula (but also more stars).

It also means that for most of this week we can see—from a dark sky site—the Milky Way arcing across the sky and streaming down to the southern horizon right after dark. Look for Jupiter and Saturn in the south; the Milky Way is right there!

However, who doesn’t like to see a super-slim crescent Moon emerge in the western sky during twilight? 

After a New Moon this Wednesday, watch out for a crescent Moon hanging in the west after dark on Thursday through Saturday. 

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Wednesday, August 19: ‘Black Moon’

What is a “Black Moon?” Although it can also be the second New Moon in a single calendar month—which happens sometimes—a “Black Moon” is better defined as the third New Moon in a season with four New Moons.

Either way, it’s a calendar quirk. More importantly, the New Moon occurs at 02:41 UTC and makes sure that this week is perfect for stargazing and looking for the Milky Way. 

Thursday, August 20 through Saturday, August 22: A crescent Moon in the west

In the nights after New Moon our satellite gradually moves away from the Sun and becomes slightly more illuminated by it each night. It will be a fabulous, but fleeting (and ultra-slim) 5%-lit sight on Thursday, August 20—look just above the western horizon at dusk.

The following night, on Friday, August 21, look to the west again, this time slightly higher, to see a 12%-lit crescent Moon. Even on Saturday, August 22, the crescent Moon—by now 20% illuminated—will remain a delicate and fascinating sight, this time with bright star Spica just below it (see above). 

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Constellation of the week: the ‘Great Square’ of Pegasus 

Or is it the “Great Diamond” of Pegasus? Rising on its side in the eastern post-sunset night sky is a vast—and one of the most geometrically precise—asterisms (shapes) in the night sky. Part of the constellation of Pegasus, the winged horse, the “Great Square” is easy to find because its corners are marked by four stars of roughly equal brightness. 

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The highest “top” star is Scheat, which is flanked by Alperatz (below, left) and Markab (below, right), with Algenib at the bottom, near to the horizon. 

Once found, you can use the “Great Square” to gauge the darkness of your location. If you can see more than five stars within its boundaries, it’s pretty dark! 

If you’re looking an hour before midnight, look underneath the “Great Square”—down to the eastern horizon—and you’ll see the planet Mars rising.

Wishing you clear skies and wide eyes.