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]
Messier 26 | |
---|---|
Observation data (J2000.0 epoch) | |
Right ascension | 18h 45m 18.0s[1] |
Declination | −09° 23′ 00″[1] |
Distance | 5,160 ly (1,582 pc)[2] |
Apparent magnitude (V) | 8.0[3] |
Apparent dimensions (V) | 14′[3] |
Physical characteristics | |
Radius | 11 ly[4] |
Estimated age | 85.3[1] million years |
Other designations | Messier 26, NGC 6694,[5] Cr 389, C 1842-094 |
Associations | |
Constellation | Scutum |
M26 spans a linear size of 22[4] light years across with a tidal radius of 25 light-years,[7] and is at a distance of 5,160[2] light years from the Earth. The brightest star is of magnitude 11[6] and the age of this cluster has been calculated to be 85.3[1] million years. It includes one known spectroscopic binary system.[8]
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]