M26, open cluster in Scutum

Image by Jim Dixon
This cluster is not so impressive as its apparent neighbor, M11. Its discoverer Charles Messier, who cataloged it on June 20, 1764, even noted that it was "not distinguished in a 3.5 foot (FL) telescope and needed a better instrument."

Nevertheless, this is a tight, beautiful open cluster with brightest stars of mag 11.9, spectral type B8. Burnham mentions about 25 stars visible in 6-8 inch scopes and about 70 fainter members, Mallas/Kreimer overall 90. Its diameter of 22 light-years appear as 15 arc minutes from the 5,000 light years distance. The Sky Catalogue 2000.0 gives a calculated age of 89 million years for this cluster.

As Kenneth Glyn Jones mentions, James Cuffey of the Kirkwood Observatory, Indiana University, reported that a striking feature of this cluster is a well-defined zone of low star density in a region of diameter 3'.1, immediately surrounding the nucleus. It is more probable that this region is obscured by dark interstellar matter than that it is a real "hole" in the stellar population.

M26 was classified as of Trumpler type II,2,r (Trumpler), I,1,m (Sky Catalog 2000), and II,3,m (Götz).