Weekend Stargazer: August 19 – 21

Dark Nebula chart
Use this illustration to identify the Northern Coal Sack and Barnard’s E. Base chart courtesy Glenn LeDrew

This weekend is one of the year’s prime, moonless periods. Indeed, were it not for the eclipse, many more star parties would have been scheduled for this weekend. But no matter if you’re on the road somewhere for the eclipse, or staying closer to home, this is a great observing window.

One class of deep-sky object demanding moonless country skies is the so-called dark nebulas. Indeed, if you can’t see the Milky Way really well from your observing site, these opaque interstellar clouds of dust and gas are impossible to spot. Two interesting examples are well placed for evening viewing this weekend.

When you look along the band of the Milky Way, you’ll notice numerous dark rifts and patches. One conspicuous area, known as the Northern Coal Sack, hides in the celestial weeds southeast of 1.2-magnitude Deneb, the brightest star in Cygnus. This feature is part of a much larger dark assemblage known as the Great Rift, which bisects the summer Milky Way for much of its length.

Another well-known dark nebula is Barnard’s E, located a few degrees northwest of 0.9-magnitude Altair, the brightest star in Aquila. Use your binoculars (or a small, wide-field telescope) to detect a ragged, E-shaped blackish blob about one degree due west of 2.7-magnitude gamma (γ) Aquilae. Observing the ghostly “E” takes some getting used to, but once you train your eye to look for an absence of starlight, you’ll be surprised at the number of other dark nebulas you can pick up with binoculars.

To read about more events, be sure to check out my regular This Week’s Sky column at SkyNews.ca.