M107 is a loose globular cluster of eighth magnitude located in Ophiuchus. It's a difficult binocular object that's much easier to spot with small telescopes. This globular was discovered by Pierre Méchain in April, 1782 and independently re-discovered by William Herschel on May 12, 1793. Herschel was also the first person to resolve it into stars. The cluster is one of the additional items that were not included in Messier's final catalogue version, but added much later by Helen Sawyer Hogg in 1947. She also added M105 and M106.
M107 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 Ophiuchi (ζ Oph - mag. +2.5). This star is located 16 degrees north of Antares (α Sco - mag. +1.0). M107 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 southeasterly direction for 9 degrees.
At magnitude +8.0, M107 appears as a faint small diffuse object through small 80mm (3.1-inch) refractors. There is a subtle increase in brightness from the outer to the inner region but it doesn't have a particularly bright centre. A 150mm (6-inch) telescope will start to resolve members at the outer edges, but the view is much better with larger scopes. Instruments of 300mm (12-inch) aperture or greater reveal a superb object with many stars spread across the entire face of the cluster. What's also noticeable is the looseness of this globular.
At least 25 known variable stars have been identified in M107. It appears to contain regions obscured by darkness, which is unusual for such objects. M107 is best observed during the months of May, June and July.
M107 Data Table
|Object Type||Globular cluster|
|RA (J2000)||16h 32m 32s|
|DEC (J2000)||-13d 03m 10s|
|Apparent Size (arc mins)||13 x 13|
|Age (years)||13.95 Billion|
|Number of Stars||100,000|