Messier 107 (NGC 6171) - wonderfuluniverse.de

Messier 107 (NGC 6171) – VdS Remote Hakos and remote

As a member of the VdS Remote Observatory Group, I again had the opportunity in 2024 to make use of the excellent facilities at Hakos, Namibia. For my imaging project of Messier 107 (M107), I employed both telescopes of the VdS remote observatory simultaneously, combining the strengths of the larger instrument for high-resolution detail with the wide-field capability of the second system. This dual-setup approach provides a deeper and more complete dataset than would be possible with a single telescope alone. In addition to my own observations, I received a high-quality LRGB dataset of Messier 107 (NGC 6171) from Telescope Live, acquired under the pristine skies of Chile in 2025.

Messier 107, or M107, is a globular cluster in the constellation Ophiuchus and one of the faintest and loosest objects in the Messier catalog. It is also known as NGC 6171 and sometimes the Crucifix Cluster. Although it looks modest in small telescopes, it is actually a dense, ancient swarm of stars bound together by gravity.science.

M107 lies about 20,000–21,000 light-years from Earth, near the Galactic plane and roughly 9,800 light-years from the Galactic Center. Its apparent size is about 13 arcminutes across, which corresponds to a real diameter of roughly 80 light-years. Its apparent visual magnitude is around 8.8–8.9, so it is visible in binoculars from a dark site and is a fairly easy telescopic target in summer.science.

Globular clusters are old, tightly bound systems containing hundreds of thousands of stars, and M107 is no exception. It is classified as a Class X globular cluster on the old Shapley–Sawyer concentration scale, meaning it is relatively loose compared with the most compact globulars. That loose appearance is one reason it can seem less dramatic than brighter clusters like M13, even though its stellar population is rich and ancient.

M107 is thought to be extremely old, with estimates around 12–14 billion years. That puts it among the oldest known globular clusters and means it formed early in the Milky Way’s history. Its stars are metal-poor, with an iron abundance around [Fe/H] ≈ -0.95, showing that they formed before the Galaxy had been heavily enriched by earlier generations of stars. In plain terms, M107 is a fossil relic from the Milky Way’s youth.

The cluster is also notable for containing a significant number of variable stars. Sources mention 22 to 25 known variables, including RR Lyrae stars and at least one probable SX Phoenicis variable. RR Lyrae variables are especially valuable because they are old, pulsating stars often used to probe distances and cluster properties. M107 also contains blue stragglers, which are stars that appear younger and bluer than expected for such an old cluster.

M107 is moving toward us at about 147 km/s. Because it lies close to the Galactic plane, it may be affected by the Milky Way’s tidal field more than many higher-latitude globular clusters. Some studies estimate its mass at roughly 60,000 to 180,000 solar masses, though the exact number depends on the method used. That is a lot of mass, but spread over a surprisingly loose volume.

M107 has an interesting discovery history. It was found by Pierre Méchain in 1782 and independently observed by William Herschel in 1793, but it was not added to the Messier catalog until 1947 by Helen Sawyer Hogg. That makes it one of the last Messier objects to be formally recognized. Its late inclusion is a reminder that the Messier list was assembled gradually and corrected over time.science.

For observers, M107 is a rewarding target because its loose structure makes it relatively easy to resolve in a small-to-medium telescope. From a dark sky site it can be seen in binoculars, but it becomes much more impressive in an 8-inch telescope or larger, where many stars begin to separate into a grainy halo. The best time to observe it is during the summer months, especially July.

All data calibration, registration, and final processing were performed in PixInsight.