Globular star clusters are a symmetrical collection of ancient stars (up to a million such stars) which are bound together gravitationally.
Recent estimates indicate that about 150-200 globulars exist throughout our galaxy with only three being readily visible to the naked eye
(the Andromeda Galaxy has been estimated to contain approximately 500 globular clusters). Since most of the globular clusters are more common
in the southern hemisphere, scientists have deduced that our sun must lie away from the galactic core of the Milky Way. One of the most
beautiful such globular clusters is M13 in Hercules.
Note: A survey of the POSS (Palomar Observatory Sky Survey) plates during the 1950's by various astronomers including Edwin Hubble, Halton Arp and George Abell revealed fifteeen new globular clusters which are diverse in both apparent diameter (1.8' to 10.9'x8.8') and magnitude (9.2 to 15.1). Some of the Palomar globulars (ex. PAL 6-7, 9-11) are typical in both size and distance but dim due to intervening galactic dust; other clusters, such as PAL 3-4 and 14, are significantly larger but lie at the outer limits of our galaxy. Similar to the Abell catalog of planetary nebulae, this particular list of globular clusters is a popular target of observers with large-aperture instruments such as Dobsonians and including an annual "Palomar marathon".
Note: PAL 13 in Pegasus is a globular cluster with a weakly concentrated core and as indicated by the image below and its Trumpler classification of "XII". It is characterized with a surface brightness of 17.7 mag/arc-min2, thus making it one of the dimmest globular clusters within the PAL catalog as well as the Milky Way and which represents a very formidable challenge for observers with large-aperture instruments. Its apparent diameter of approximately 1.8 arc-minutes makes PAL 13 also one of the smallest members within the PAL catalog. PAL 13 lies at an impressive average distance of 84,100 light-years away, thus making it a galactic halo globular cluster within the Milky Way. A recent study found PAL 13 to be 10.5 + 1.0 billion years old! PAL 13 was discovered by American astronomer A.G. Wilson in 1953.
Please click on the image below to display in higher resolution (1200 x 900)
C 2304+124, ZWG 430.061
RA / Dec:
23h 06m 45s /
+12° 46' 19"
Oct 09-10, 2009
20:25 - 23:25 UT+3
AP 160 f/7.5 StarFire EDF
AP 1200GTO GEM
SBIG LRGB filters
1.17" per pixel