Sky and Telescope - May 2012 - (Page 60)

Alan Whitman Going Deep

The Coma Galaxy Cluster
This ghostly swarm is fantastically rich and compact. At a distance of about 350 million light-years, the
Coma Galaxy Cluster (Abell 1656) is the nearest of the massive spherical galaxy clusters, with thousands of member galaxies. These are mostly ellipticals and lenticulars, so even the brightest ones show few details. Instead, an observer’s satisfaction comes from the hunt and from seeing many galaxies simultaneously. The Coma Cluster isn’t as popular as it should be, perhaps because it had bad press early on. The classic late 1970s observing guide Burnham’s Celestial Handbook says: “NGC 4889 and 4874 are the only two members of the Coma Cluster of Galaxies which are likely to be detected in most amateur telescopes.” But one spring night in 1983 I spent two hours in the cluster with my 8-inch f/6 Newtonian, guided only by a photo from the Palomar Observa+30° 13h 00m 4889 41 4874 31 12h 30m

+25°
Star magnitudes 4 5 6 7 8

COMA BERENICES

tory Sky Survey. In addition to the two giant ellipticals promised by Burnham, I found NGC 4921 and 4860 — so I was very pleased with the results of my hunt. Now that I know the Coma Cluster well, my ancient 8-inch also reveals NGC 4911 and elongated NGC 4895 without too much diﬃculty, as well as glimmers of NGC 4865, 4869, and 4881. As Guy Mackie’s sketch on the facing page shows, an increase in aperture to a 12.5-inch Dobsonian reveals a horde of 14th- and 15th-magnitude galaxies. Mackie comments: “What’s most striking is my ability to ﬁ nd much more in the ﬁeld than I saw at ﬁrst blush.” In recent years I have spent many nights working through the Coma Cluster with my observatory’s 16-inch f/4.5 Newtonian on an equatorial mount. This month’s tour will concentrate on the richest clump of galaxies, occupying an oval area outlined by NGC 4881 to the north, NGC 4921 and 4911 to the southeast, and NGC 4860 to the northwest. The 16-inch found 37 galaxies swarming within this small area — only 38′ × 24′ — with the long axis stretching northwest to southeast. My planetarium program charts stars to magnitude 15.0 for starhopping, but it’s necessary to galaxy-hop in many star-sparse areas. I used a 12-mm eyepiece yielding 152× and a 24′ ﬁeld of view, supplemented on steadier nights by an 8-mm eyepiece giving 229× and a 16′ ﬁeld.

The Northeast Side of the Oval
M64

4944 4931 +28° 4961 41 4957 4926

4895 4881 4907 4889 4911 4853 4921 4860 4865 4874

4848

4816 4839 4807 4798

NGC 4881 and NGC 4895 are two of the brightest galaxies on this tour. NGC 4881 sports a bright nucleus, and NGC 4895, a lenticular, is elongated 5:2 and brightens gradually in the middle, rising to a nucleus. The next galaxy in line, NGC 4907, has a higher published surface brightness than the preceeding two, but I ﬁnd it less obvious at the eyepiece. On two nights I caught glimmers of the nearby 15th-magnitude galaxy PGC 44784. This tiny mote is paired with a 14th-magnitude star only 27″ to its south-southeast.
The Coma Galaxy Cluster is easy to locate one-third of the way from Beta to Gamma Comae Berenices. Only the brightest galaxies of the Coma Cluster are shown on this chart. See the photograph on page 62 for details of the highlighted region.

COMA BERENICES
+27°
Star magnitudes h m 5 6 13 05 9 10 11 7 8

4827 4819 13h 00m

4789A 4789 12h 55m

60 May 2012 sky & telescope

Table of Contents for the Digital Edition of Sky and Telescope - May 2012

Sky and Telescope - May 2012
Table of Contents
Spectrum
Letters
75, 50 & 25 Years Ago
News Notes
Saturn’s Raging Superstorm
Stars Above, Earth Below: Astronomy in National Parks
The Remarkable Case of Comet Lovejoy
In This Section
May’s Sky at a Glance
Binocular Highlight
Planetary Almanac
Northern Hemisphere’s Sky
Sun, Moon, and Planets
Celestial Calendar
Exploring the Solar System
Deep-Sky Wonders
Going Deep
S&T Test Report
New Product Showcase
Telescope Workshop
Planetary Imaging with Your DSLR Camera
Gallery
Focal Point

Sky and Telescope - May 2012