by | Jul 1, 2022 | 0 comments

M12. Photo © Scott Rosen.

Ophiuchus is a large constellation that lies high in the southern sky on midsummer evenings. This constellation lies just north of the constellation Scorpius and just west of the band of the Milky Way.

Ophiuchus contains a couple of large open star clusters that are good targets for a binocular or a telescope at low magnification. One of these clusters, IC 4665, lies about 1.5° northeast of the star Cebalrai, in the northern part of Ophiuchus. IC 4665 is a sparse cluster with relatively bright component stars, so it is fairly easy to resolve with binoculars.

Another open cluster, NGC 6633, lies about 10° east of IC 4665. Like IC 4665, many of the component stars of NGC 6633 are relatively bright. However, the NGC cluster is much smaller than its IC neighbor, so it can benefit from slightly higher magnifications.

One of the finest double stars in Ophiuchus lies near these two open clusters. This double, 70 Ophiuchi, is the easternmost member of a small triangle of stars that lies roughly 5° east of Cebalrai. This double star consists of a yellow primary star and an orange secondary star that are currently separated by about 6”. Moderate magnification (75–125×) will nicely split this double.

Ophiuchus contains a couple of planetary nebulae, the brightest of which is NGC 6572, also known as the Blue Racquetball Nebula. To find this nebula, first find the star 71 Oph, which lies about 6° straight north of 70 Oph. NGC 6572 lies about 2° southeast of 71 Oph. True to its name, this nebula looks like a fuzzy bluish or greenish spot of light. It is relatively small, but you should be able to identify it at moderate to high magnification by its fuzzy appearance and color.

Ophiuchus is particularly rich in globular star clusters, with 7 from the Messier catalog and many more from the NGC catalog. Two of the constellation’s finest globular clusters are M10 and M12. Both of these clusters lie near the center of Ophiuchus. M10 sits just 1° west of the star 30 Oph, and M12 lies 3° northwest of M10. Both clusters are similar in size and brightness, but you may find that M12 is slightly easier to resolve because its core is less densely packed with stars than the core of M10. Like all globular clusters, these two look best at fairly high magnification. However, this pair is also a good binocular target because both clusters are visible as small fuzzy spots in the same field of view.

Star map, Ophiuchus, Serpens Cauda, Scutum, Libra, Serpens Caput

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