Deep sky Ophiuchus
Globular cluster M12 lies some 8° east-northeast of Yed Posterior (Epsilon [ε] Ophiuchi). It glows at magnitude 6.1 and measures 14.5' across, roughly half the width of the Full Moon.
Because globular cluster M10 lies some 14,000 light-years away, intervening dust dims its stars by nearly a magnitude. Still, it glows at magnitude 6.6 and is an easy catch through binoculars.
Ray and Geoff Weavill/Adam Block/NOAO/AURA/NSF
The Box Nebula (NGC 6309) glows softly at magnitude 11.5. However, because it spans only 18", you’ll have to spot it through a 6-inch or larger telescope. Crank the power past 250x to see the Box’s shape; an Oxygen-III filter will help.
The Snake Nebula (Barnard 72) is a cloud of dust and cold gas. Your best views of it will come through a telescope and eyepiece combo that yields a field of view around ½°. To find it, look 1½° north-northeast of Theta (θ) Ophiuchi.
Jim and Janet Castano/Adam Block/NOAO/AURA/NSF
NGC 6384, the single spiral galaxy in Ophiuchus worth observing, is magnitude 10.4. It lies 3.7° northwest of Cebalrai (Beta [β] Ophiuchi) and measures 6.2' by 4.1'. You’ll see its roughly rectangular shape through an 8-inch scope at 150x.
The Captain Hook Cluster (NGC 6633), located toward the upper right of this image, is an open cluster that shines at magnitude 4.6 and measures 27' across. You’ll find it 8° west-northwest of Alya (Theta [θ] Serpentis). Keep the magnification low through large scopes so you don’t look “through” this cluster. Open cluster IC 4756 in Serpens is also visible at left here.
The Emerald Nebula (NGC 6572) lies 2.2° south-southeast of 71 Ophiuchi. Although this planetary is small, it has a high surface brightness and is quite colorful. This shot was taken using a 5.1-inch refractor, but an 8-inch or larger scope will reveal the Emerald’s oval shape.
The Black Swallowtail Butterfly Cluster (IC 4665) — seen here above the cyan-tinted star Cebalrai — is a relatively bright open cluster at magnitude 4.2. It won’t look bright, however, because it measures 70' across. That means it covers 5½ times the area of the Full Moon. Observe it through a low-power eyepiece.
