Messier 107: Globular Cluster in Ophiuchus

M107 is the faintest of the seven globular clusters Messier's list holds in Ophiuchus. It is easy to find, less than 3° from a bright star, and it makes a good contrast with its showier neighbors M10 and M12 about 10° to the north.

What it is

A globular cluster is a dense ball of old stars, many thousands to hundreds of thousands of them, orbiting in the halo of the Milky Way. M107 is one of the more loosely packed examples. It lies about 18,400 light-years away, and its 13′ apparent size corresponds to roughly 70 light-years across. Photographs show dark patches of dust in front of and around the cluster, which dims it and gives it a slightly uneven look. For brighter globulars nearby, see M10 and M12 in the middle of Ophiuchus, and M4 in Scorpius.

When to see it

M107 is a summer object, highest around midnight in early June and well placed in the evening from June through August. It lies south of the celestial equator, so from about 40°N it reaches only about 37° above the southern horizon; choose a night with a clear, dark southern sky. From the Southern Hemisphere it rides much higher, reaching about 68° from 35°S.

How to find it

Start at Zeta Ophiuchi, a second-magnitude star in the southwestern part of Ophiuchus, above and to the left of Antares as seen from northern latitudes. M107 lies about 2.7° south-southwest of Zeta, roughly on the way toward Antares but much closer to Zeta. Put Zeta at the edge of a binocular field and the cluster should appear near the opposite edge.

What you will see

In binoculars under a dark sky, M107 is a small, faint, round glow with no stars resolved; from the suburbs it is hard to spot. A 70–100 mm telescope shows a soft, round haze with a slightly brighter center and, at higher power, a grainy texture at the edges. A 200 mm or larger telescope resolves many of the outer stars and shows the cluster as a loose, irregular ball, with some observers noting darker gaps across it. No filter is needed.

History

Pierre Méchain discovered M107 in April 1782, making it the last of all the Messier objects to be discovered, but it never appeared in Messier's published catalog. William Herschel independently found it in 1793 and was the first to resolve it into stars. In 1947 Helen Sawyer Hogg added it to the list as M107, one of the objects from Messier's and Méchain's notes that were added in the 20th century.