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 14 in Hercules 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 16.1 mag/arc-min2 with its brightest star being only of magnitude 17.6, thus making it one of the dimmest globular clusters within the PAL catalog along with PAL 3 in Sextans and PAL 4 in Ursa Major. Its apparent diameter of approximately two arc-minutes makes PAL 14 also one of the smallest members of the PAL catalog. PAL 14 lies at a distance of 225,000 light-years away, thus making it one of most distant globular clusters within the Milky Way. PAL 14 was discovered by Canadian astronomer Sydney van den Bergh in 1958 and later confirmed by Halton Arp to be a globular cluster (see here).
Please click on the image below to display in higher resolution (1200 x 900)
Arp 1, C 1608+150
RA / Dec:
16h 10m 59s /
14° 57' 29"
June 14-15, 2009
22:45 - 01:35 UT+3
AP 160 f/7.5 StarFire EDF
AP 1200GTO GEM
AstroDon TruBal CRGB
1.17" per pixel