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Hickson
94 is a compact galaxy group with a total of seven members.
Measurements of the gas temperature between the galaxies and the
unabsorbed X-ray luminosity indicate that this is a true galaxy
cluster. The redshift (Z) of the member galaxies is 0.04,
representing a light travel time of 600 million years from the
cluster to your eye.
The
cluster was apparently discovered by William Herschel, who merely
noted, "4 or 5 small stars with nebulosity."
 The
brightest member is NGC 7578B (aka PGC 70934, MCG 3-59-25, Uppsala
12478), a 14.7 magnitude elliptical galaxy that subtends 52" x
44". Nearby is NGC 7578A (aka Arp 170, PGC 70933, MCG
3-59-24, Uppsala 12477), a 14.9 magnitude lenticular that subtends
23" x 18". Note that different sources may switch
the A and B designations on these two. NGC
7578A/B overlap and are apparently interacting. The galaxies
themselves are very faint, but their luminous cores give them away.
At lower magnification or to the undiscerning observer, these cores
appear very much like stars embedded in a slight haze.
Nearby
lie two other galaxies within reach of larger amateur instruments.
PGC 70943 is a 16.2 magnitude spiral galaxy that subtends 28" x
13". Despite the faint magnitude, the surface brightness
of this galaxy is relatively high (22.3 mag/arc-sec2).
This galaxy is listed as interacting with an associated bar.
As with the others the core of PGC 70943 is most easily seen and
appears stellar.
PGC
70936 is a tiny (10" x 6") 16.3 magnitude lenticular
galaxy that lies very close to the NGC 7578A/B pair. This tiny
galaxy appears in the eyepiece as a very faint star.
Unfortunately, a nearby star is easily confused with it (see image).
The
image above shows how small and starlike these galaxies are.
The field (gray circle) in
an 18-inch f/4.5 at 60x. North is down and east is to the
right.
At
the eyepiece the cluster appears as a few faint stars embedded in a
very faint haze. A night of good seeing and high magnification
(at least 250x) are recommended. |
