M-4, globular cluster

Globular Star Cluster M-4 (NGC 6121) in Scorpius

There are two images of the cluster below. The first is a a color image covering only the inner part of the cluster taken with our 20-inch telescope. The second is a wide field black & white image taken thru our 80mm VERNONscope refractor.

Globular Cluster, M-4
A CCD image taken with an STL-1301E CCD camera thru our 20-inch F/8.1 telescope working at F/5. The field of view is about 20x20 arc minutes. This image only shows the inner portion of the cluster. M-4 was only 19 degrees above the horizon when this image was taken.

Globular Cluster, M-4
A CCD image taken with an Starlight Xpress MX-716 CCD camera thru our VERNONscope 80mm refractor working at F/6.25. The field of view is about 60 x 45 arc minutes.

P.L. de Cheseaux (Discovered M-4 in 1746):

'Close to Antares . . . it is white, round and smaller than the preceding ones. I do not think it has been found before.'

Charles Messier (May 8th, 1764):

''Cluster of very small stars: with an inferior telescope it appears more like a nebula; this cluster is situated near Antares and on the same parallel. Observed by M. de la Caille and reported in his catalogue. Reviewed 30th Jan. and Mar. 22nd 1781. Diam. 2.5 arc min.'

Quote from Burnham's Celestial Handbook:

"Fine globular star cluster, one of the largest objects of its type, and also one of the nearest. It is probably the easiest of all the bright globulars to locate; merely point the telescope to Antares, and then move 1.3° directly west, and there you are. M-4 is located quite easily in binoculars and may even be detected without optical aid under good sky conditions............."

Description of M-4 in The Deep Sky Field Guide to Uranometria 2000 (c) Willmann-Bell, Inc.:

Brightest stars = magnitude 13.4;
horizontal branch stars magnitude = 15.8;
concentration: 9 (low =12 high = 1).

This cluster was discovered in 1746 by de Cheseaux. Current estimates place M-4 at a distance of 10,000 light years, with an age of 14 billion years. (But Click here for the latest news on Globular Star Cluster distances and ages!!).

M-4, NGC 6121
Magnitude: 5.9
Constellation: Scorpius
RA: 16h 23m 36.0s
Dec: -26° 32' 00" Epoch 2000
Size (mins) 26.3
Classification: Globular Cluster

George Normandin, KAS

August 19thst, 2006