M107 is a loose eight-magnitude globular cluster located in Ophiuchus that's a difficult binocular object but much easier in small telescopes. It was discovered by Pierre Méchain in April, 1782 and then independently re-discovered by William Herschel on May 12, 1793. Herschel was also the first person to resolve M107 into stars. This cluster is one of the additional catalogue items that weren't included in Messier's final version but added much later by Helen Sawyer Hogg in 1947. She also added M105 and M106 since it seems probable that Méchain had also intended to include these items to a future edition of the catalogue.
The globular is located 20,900 light-years from Earth and spans 13 arc minutes of apparent sky, which corresponds to a spatial diameter of 80 light-years. It contains 100,000 stars and has an estimated age of 13.95 billion years, making it one of the oldest known globulars.
Locating M107 is relatively easy as its positioned 2.75 degrees southwest of zeta Oph (ζ Oph - mag. +2.5). This star is located 16 degrees north of Antares (α Sco - mag. +1.0) and can be also found by imagining a line connecting Yed Prior (δ Oph - mag. +2.7) with Yed Posterior (ε Oph - mag. +3.2) and extending it in a south-easterly direction for 9 degrees. The cluster is best observed during the months of May, June and July.
At magnitude +8.0, M107 appears as a faint small diffuse object through a small 80mm (3.1-inch) telescope. There is a subtle increase in brightness from the outer to the inner region but no particularly bright centre. A 150mm (6-inch) scope will start to show the brighter stars around the outer edges but the view is much better with larger telescopes. Instruments of 300mm (12-inch) aperture or greater reveal an incredible site, many stars visible across the entire face of the globular. What's also noticeable is the looseness of this cluster.
At least 25 known variable stars have been identified in M107. It seems to contain some regions obscured by darkness, which is unusual for globular clusters.
M107 Data Table
|Object Type||Globular cluster|
|RA (J2000)||16h 32m 32s|
|DEC (J2000)||-13d 03m 10s|
|Apparent Size (arc mins)||13 x 13|
|Number of Stars||100,000|