Open Cluster Messier 23

Messier 23
Messier 23: Section of the Digitized Sky Survey [147]

Object Description

The galactic star cluster Messier 23 was probably first sighted by Charles Messier in June 1764. Although Messier described it as a cluster 15 arc minutes in diameter with stars very close together, he added M 23 to his list of comet-like objects. John Herschel found around 100 stars from 9th to 13th magnitude in this group, which appear more or less evenly scattered with a slight concentration towards the center. A number of stars are formed into curved arcs and chains, which suggest the shape of a Chinese temple to the imaginative observer or which look something like oriental calligraphy.

According to the color-brightness diagram, the majority of stars appear to be reddish main sequence stars. The brightest members are of type B9. Several G-type giant stars exist in the group - the brightest example in the main mass of the cluster can be found in the small elliptical formation of six stars in the center: it is the westernmost star of this flat ring. The star density in the center is estimated at around 31 stars per cubic parsec. M 23 is in front of an extensive dark cloud. The distance of the cluster is a little more than 2000 light years, the diameter about 15 light years. [1, 4]

«Revised New General Catalogue and Index Catalogue» Dr. Wolfgang Steinicke, 2021 [277]
DesignationNGC 6494
TypeOCL (III1m)
Right Ascension17h 56m 56.0s
Declination-19° 00' 42"
Diameter25.00 arcmin
Visual magnitude5.5 mag
Dreyer DescriptionCl, B, vL, pRi, lC, st 10…
IdentificationM 23, OCL 30, ESO 589-SC22

Finder Chart

The star cluster Messier 23 is located in the constellation Sagittarius. It can best be seen in the months of June to August. Then the constellation is highest above the southern horizon.

Chart Messier 23
Chart created using SkySafari 6 Pro and STScI Digitized Sky Survey. [149, 160]


1«Atlas der schönsten Himmelsobjekte» von Hans Vehrenberg; 4. Auflage von «Mein Messier-Buch», Nachdruck 1985; Treugesell-Verlag KG, Düsseldorf
4«Burnham's Celestial Handbook: An Observer's Guide to the Universe Beyond the Solar System» by Robert Burnham; Dover Publications, Inc.; Voume I: ISBN 0-486-23567-X; Volume II: ISBN 0-486-23568-8; Volume III: ISBN 0-486-23673-0
147Aladin Lite; (2020-12-23)
149SkySafari 6 Pro, Simulation Curriculum;
160The STScI Digitized Sky Survey;
277«Historische Deep-Sky Kataloge» von Dr. Wolfgang Steinicke; (2021-02-17)