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 10 in the constellation of Sagitta is a globular cluster with a very weakly concentrated core and as indicated by the image below and its Trumpler classification of "XII". It is characterized with a surface brightness of 15.7 mag/arc-min2 which is relatively dim amongst the members of the PAL catalog and which represents quite a formidable challenge to observers. Its apparent diameter of approximately 3.5 arc-minutes makes PAL 10 also one of the smallest members of the PAL catalog. PAL 10 lies at a distance of 19,200 light-years away, thus making it one of closest globular clusters within the Milky Way. PAL 10 was discovered by American astronomer Albert George Wilson in 1955.
Please click on the image below to display in higher resolution (1200 x 900)
RA / Dec:
19h 18m 02s /
18° 34' 22"
June 20, 2009
01:20 - 04:15 UT+3
AP 160 f/7.5 StarFire EDF
AP 1200GTO GEM
AstroDon TruBal CRGB
1.17" per pixel