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Observing Abell 2151: The Hercules Cluster

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Observing Abell 2151
Observing Abell 2151: The Hercules Cluster
Alan Kane - 7/09

Click on the image above for a full size (and more readable/useable) image.

The area in Hercules bordering Serpens Caput has always interested me due the remoteness of many of the visible galaxies in that area, many of which are members of the Hercules Supercluster over 500 million light years away. 

A couple of months ago, I turned my main attention to the famous A2151 cluster to see how many galaxies were detectable within 1º of the centre.  The cluster is easy to locate being just east of the bright star HD 144149. Go to the 5th mag star 5 Hercules and then drift about 30’ east to 7th magnitude  HD 144149. A reasonable amount of magnification > 200x worked best for this cluster as all its members are very small mainly due to their remoteness.

All the following observations were made with an 18 inch f4.5 obsession with a 7mm Nagler giving 292x on the 3rd and 23rd May 2009 from an observing site 16 miles to the west of Auckland central.  The NLEM at the Zenith was about 6.0 and the galaxy cluster was at its maximum height of about 35º above the northern horizon.

NGC 6053, 6055 & IC 1190

A nice group all visible in the same field of view. 6053 was the smallest but brightest showing as a near stellar spot. NGC 6055 just 2’ W showed as a fainter slight larger oval spot.  IC 1190 4’ NW of 6053 was of similar size but much fainter requiring av.

NGC 6061, IC 1189 & 1191

Another group of three in the same field of view.  6061 was the brightest showing as a fairly small oval with a slightly brighter centre. IC 1189 4’S was a tiny faint spot just visible with direct vision while IC 1191 3’ E was a barely perceptible small glow with av.

NGC 6056 & MCG +03-41-105

Widish 5’ pair with 6056 being slightly brighter but both appearing similar size

NGC 6043, 6044, 6045, 6047 and PGC 57020

Both 6043, 6045 & 6047 form a nice neat little trio which were easily visible. 6047 was a very small bright spot forming a ‘double’ with a 13th mag star just 20” NW.  Less than 2’ N was 6045 which was very small, fairly bright and extended. The tiny faint galaxy appearing in contact with 6045’s eastern end wasn’t visible – I’d be interested to know if anyone has observed it.   Another 2’ to the NW of 6045 we come to 6043 which is a double system but appeared as a small pretty faint round spot.  7’ N of 6045, 6044 was visible as a faint very small round spot. 2’ S of 6044, I glimpsed the much fainter PGC 57020 which was visible about 50% of the time with av as a tiny near stellar spot.

NGC 6050, 6054, IC 1182, 1183 & 1185

6054,  IC 1182 & 1185 are in a rough line 7’ S of NGC 6045 with all appearing very faint and of similar very small size.  6055 2’ N of 6054 is much fainter requiring av while double galaxy 6050 another 2’ N showed as a very faint diffuse patch about 1’ across.

NGC 6040 area (10’ E of 7th mag HD 144149

Very nice group 6 galaxies visible.  6040 & 6040B clearly showed two nuclei in a common faint halo. 6041 & 6041B initially showed as one but on closer inspection their 15” apart nuclei were also split.  Just 1’ W of the 6041 pair was IC 1170 which showed as an extremely faint, very small patch about 50% of the time with av. Another 1.5’ SE of 6041/6041B lay NGC 6039 which was visible as a faint, very small almost round spot.

Interacting pair IC 1178 & 1181

This close pair is located about 15’ ESE of NGC 6041. IC 1178 was the easiest showing as a very faint, very small round spot.  IC 1181 just 30” S was of similar size but extremely faint requiring av.

Over a couple of nights I managed to see at least 26 members and there were some more I didn’t have time to try for but will return again.  There are numerous others I’ve seen in the surrounding areas including neighboring abell clusters.


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