|Rektascenzija||17 : 56.8 (u:m)
|Deklinacija||-19 : 01 (sto:m)
|Razdalja||2.15 (*1000 sv.l.)
|Vizual. magnituda||6.9 (mag)
|Zorni kot||27.0 (loc min)
Open cluster M23 is another glorious sight for small telescopes and binoculars in the summer Milky Way. It is one of Messier's authentical discoveries. At a distance of 2,150 light years, the apparent diameter of this 6-7th mag object, 27 arc minutes, corresponds to about 15 light years (Kenneth Glyn Jones' figure of 35' would correspond to about 20 light years). It contains at least about 150 proven member stars. M23 was classified by Trumpler as I,2,r, while Götz assigns it to class II,2,r, and the Sky Catalog 2000 gives III,1,m.
The hottest stars in M23 are of spectral type B9, the brightest star is of
magnitude 9.21. The age of M23 has been estimated at 220 million years
(Sky Catalog 2000) and 300 million years
(by G. Meynet's Geneva Team).