NGC 6540, Djorg 3

Globular Cluster NGC 6540 (Djorg 3), in Sagittarius

Distance from Sun:
17.3 kly
Distance from Galactic Center:
9.1 kly
Apparent Diameter:
9.5 arc min
9.30 mag vis
Radial Velocity:
-17.7 +/- 1.4 km/s
Abs. Mag:
-6.35 Mag vis
Discovered by William Herschel on May 24, 1784.
Independently rediscovered as globular cluster (Djorg 3) by Djorgovski in September 1986.
Identified and confirmed as globular by Bica, Ortolani and Barbuy in 1994.

NGC 6540 was discovered by William Herschel in 1784 and cataloged as H II.198. While Herschel classified it as a "faint nebula," indicated by his classification in the second group of deepsky objects, this object was longly listed as open cluster, e.g. by Collinder who designated it Cr 364. S. Djorgovski independently "rediscovered" it in September 1986 without noting its identity, when looking for obscured globular clusters in the IRAS Point Source Catalog, labeled it Djorg 3, and suspected it to be a globular cluster (Djorgovski 1987). It was finaly Bica (1994) who identified it with the NGC object, and confirmed its nature as a globular cluster.


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Hartmut Frommert [contact]