Messier 26 | |
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![]() Open cluster Messier 26 Credit: Hillary Mathis, Vanessa Harvey, REU program/NOIRLab/NSF/AURA | |
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 |
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]
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]