Messier 26, also known as NGC 6694, is an
open cluster of
stars in the southern
constellation of
Scutum. It was discovered by
Charles Messier in 1764.[a] This 8th magnitude cluster is a challenge to find in ideal skies with typical
binoculars, where it can be, with any modern minimum 3-inch (76 mm)
aperture device. It is south-southwest of the open cluster
Messier 11 and is 14
′ across.[3] About 25 stars are visible in a telescope with a 150–200 mm (6–8 in) aperture.[6]
An interesting feature of M26 is a region of low
star density near the nucleus. A hypothesis was that it was caused by an obscuring cloud of
interstellar matter between us and the cluster, but a paper by
James Cuffey suggested that this is not possible and that it really is a "shell of low stellar space density".[9] In 2015, Michael Merrifield of the University of Nottingham said that there is, as yet, no clear explanation for the phenomenon.[10]
^Mermilliod, J. -C.; et al. (October 2007), "Red giants in open clusters. XIII. Orbital elements of 156 spectroscopic binaries", Astronomy and Astrophysics, 473 (3): 829–845,
Bibcode:
2007A&A...473..829M,
doi:10.1051/0004-6361:20078007.