Globular Star Cluster
Spiral Galaxy MCG 3-53-11
CCD image taken with a Starlight
Xpress MX-716 CCD camera thru a 20-inch F/8.1 telescope working at F/5.
The field of view is about 5x7 arc minutes with North at the top.
The small object at the lower
right is 16th magnitude Spiral Galaxy MCG 3-53-11.
Description of Globular Star Cluster
NGC 7006 in
Burnham's Celestial Handbook:
An exceedingly remote globular star cluster, probably
the farthest object of its type with the exception of the well known NGC
2419 in Lynx, which may actually be an extra-galactic object. NGC 7006
appears to be about 150,000 light years from the center of our Galaxy and
some 185,000 light years from the Solar System. This is almost comparable
to the distances of the Magellanic Clouds and suggests that these two clusters
might possibly be regarded as extra-galactic objects.
Despite its vast distance, NGC 7006 is visible in
a 6-inch telescope as a fuzzy spot of magnitude 11.5, about 1' in apparent
size. The diameter increases to about 2.2' on long exposure photographs,
giving a true size of about 120 light years. This is one of the most difficult
of all globulars to resolve, since even the brightest members are of the
16th magnitude. Allowing for a certain loss of light through absorption
by interstellar dust, the true luminosity of the cluster appears to be
about 130,000 times that of the Sun, and the absolute magnitude is near
-8. The integrated spectral type is F1. This cluster shows a very large
radial velocity of 215 miles per second in approach.
Harlow Shapley's observations (in 1930) of
eleven RR Lyrae type stars in NGC 7006 showed it to be about five times
as remote as M3 or M5, certainly the most distant globular known at the
time. On the other side of the Galaxy the most distant system appears to
be NGC 2298 in Puppis; the separation of these two globulars must be slightly
over a quarter of a million light years. The size of the Galaxy is thus
more than doubled when these clusters are used as boundary markers! The
validity of this approach, however, now appears somewhat doubtful owing
to the .... discovery of a number of other very distant and extremely faint
globulars on the Palomar 48-inch Sky Survey plates. Some of these are evidently
true inter-galactic objects, so it now appears possible to regard NGC 7006
and NGC 2419 as either the most distant members of the Galaxy or the nearest
of the intergalactic clusters.
- NGC 7006
- Magnitude: 10.6
- Constellation: Delphinus
- RA: 21h 01m 30.0s
- Dec: +16° 11' 00"
- Size (mins): 2.8'
- Classification: Globular
George Normandin, KAS
January 2nd, 2005