The globular Cluster M4 (NGC6121) is one of the nearest globuar clusters to our solar system.It includes about 10.000 stars with 43 variables and its real diameter is abut 75 light-years.
Visually it can be detected even in 2inch telescopes as a fuzzy ball and because of its small distance to Antares,it is easy to find.( 5.9 mag,diameter 25´)An overview of of this fantastic skyregion can be viewed here.
Due to strong interstellar-dust absorption,its color is more yellow-red than one would expect.
In 6-8inch telescopes you can detect a bar of about 3´lenght that consists of about 20 stars of 11 th magnitude,orientated N-S,which was first detected by William Herschel in 1783.
M4 itsself was first detected by P.L.Cheseaux in 1746 and was one of the fist objects to be added by Messier to his famous catalog.
RA: 16h 23m 35.22s
Decl.: –26° 31′ 32.7"
RGB=7x1200s each,total time:7.0h, Seeing: 0.9-1.3",
80cm f/7 AstroOptik-Keller corrected Cassegrain, FLI Proline 16803, Baader-RGB-filters, Promt7 CTIO/UNC Chile,remote controlled
image-processing: Bernd Flach-Wilken
this is a view of 80% CCD-field size:
here you can detect the central-bar,visible even in mid-sized telescopes (6-8inch aperture):
here is close look to M4´s core,taken with the HST.