M4 is one of the largest globular star clusters in our galaxy in terms of the number of stars in the cluster. The cluster includes over 10,000 stars in a rather loose cluster with no great central concentration. Interestingly, the population of M4 is relatively poor in giant stars. M4 was probably first observed by P.L. de Cheseaux in 1746. It was one of the first objects added to Messier catalog in May 1764. It is one of the nearest globular clusters to our solar system, at a distance of about 6000 light-years. M4 is reddened by about 0.8 magnitude due to dark nebulosity in that part of the sky, which is near the dustest region of our Milky Way from our viewing perspective. The star cluster is speeding away from us at a speed of 39 miles per second. It also has the distinction of being one of the easiest globular clusters to find, because of its proximity to Antares in the constellation Scorpius.
The globular star cluster M80 is located nearby in Scorpius.
This is a composite RGB CCD image taken with a Takahashi FCT-150 at prime focus. The CCD camera was an SBIG ST-8E using a CFW-8 color filter wheel. This image was taken from a dark sky site east of Phoenix at an altitude of about 4,000 feet.
M4 (NGC 6121)
Constellation: Scorpius
RA: 16h 23m 40.1s Dec: -26d 32' 06"
March 25, 2001
Image by Sid Leach
Superior, Arizona
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