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 9 in the constellation of Sagittarius is a globular cluster with a fairly dominant concentrated core and as indicated by the image below and its Trumpler classification of "VIII". It lies immediately below the bright carbon star SAO 187445 (mag 5.0, B-V=1.63) and just to the east of another bright carbon star (SAO 187426, mag=4.86, B-V=1.67). Palomar 9 is characterized with a surface brightness of 11.9 mag/arc-min2 and which is relatively bright amongst the members of the PAL catalog but which still represents a quite formidable challenge to observers. Its apparent diameter of approximately 3.9 arc-minutes makes PAL 9 also one of the smaller members of the PAL catalog. PAL 9 lies at a distance of 23,100 light-years away, thus making it one of the closer globular clusters within the Milky Way. PAL 9 was discovered by William Herschel on August 7, 1784 and as indicated by its inclusion in the NGC catalog (NGC 6717). The cluster was independently noted in the POSS plates by George Abell in 1955 while unaware of its earlier discovery by Herschel.
Please click on the image below to display in higher resolution (1200 x 900)
GCL 105, OCL 37
RA / Dec:
18h 55m 06s /
-22° 42' 06"
June 23, 2009
00:10 - 03:15 UT+3
AP 160 f/7.5 StarFire EDF
AP 1200GTO GEM
SBIG LRGB fiters
1.27" per pixel