From the January 2024 issue

Snake Nebula

By | Published: January 1, 2024

B72, also called the Snake Nebula, in Ophiuchus is another of Barnard’s discoveries. When observing dark nebulae such as this, you’re looking for dark places in the heavens. Such a search requires good skies where the richness of the Milky Way makes it obvious when something is obscuring it. (Earthly clouds don’t count!)

Considered relatively nearby at 650 light-years distant, B72 is compact, running 6′ in a northwest–southeast direction. It is narrow, ranging from 2′ to 3′ thick. The densest part of the dust cloud forms an S; it was called the S Nebula before the moniker Snake Nebula became popular. Its 5-light-year-long sinuous nature appears in small telescopes under skies where the Milky Way glows bright. Look about a degree and a half north-northeast of Theta (θ) Ophiuchi, a magnitude 3.25 multiple star. The area is rich in dark clouds. Look for a set of nearby “holes” (“plugs” might be more apropos) in the background glow: B68, B69, B70, and B74. (Barnard 68 is the densest and darkest of the four.)

The whole region is a wonder to scan with a wide-field telescope or large binoculars. The Snake is at the top of the Pipe Nebula, a large cloud spanning 5° in length and more than 3° in width. That’s large enough to be visible to the naked eye from latitudes with good views of the southern sky. And if the Snake and Pipe aren’t enough, they’re also part of a large nebular complex called the Dark Horse Nebula, which covers a generous 10° by 10°.