NGC 474 Galaxy Cluster The NGC 474 galaxy cluster (or group) consists of three relatively bright galaxies. They are: NGC 467 (mag. 12.9), NGC 470 (mag. 12.5), and NGC 474 (mag. 12.4). This is a fascinating little trio of galaxies, especially because the catalogued largest one, NGC 474, does not visually appear as large as nearby NGC 470. The reason is that NGC 474 has an outer halo that is extremely faint. It has been seen in 18-inch instruments and larger as just a faint brightening of the black background.

In 1994, Roger Ivester wrote a paper concerning the apparent missing matter in NGC 474. The text of that report is quoted as follows: 

The NGC 470 474 Controversy – Missing Matter Revealed by Roger Ivester:

My observations on Thursday, December 1, 1994, included three spiral galaxies in Pisces, NGC 467, NGC 470, and NGC 474, each separated by only a few minutes of arc. It became apparent immediately that NGC 470 was the largest and most easily seen of the group, but when I referred to the NGC 2000.0 Catalogue, it listed NGC 474 as being over twice as large as either NGC 470 or NGC 467. 

At this point, I concluded that NGC 474 must have a halo that could not be seen visually, or at least not from my back yard. The next day I located a photo of this group, but it did not show a faint outer arm, nor was any halo apparent. The view appeared very similar to what I had seen through my telescope. 

I decided that another observation was needed, and made a note in my log to “view at next session.” On Monday, December 16, I went to a dark site in the South Mountains about 30 minutes north of my home in Boiling Springs, North Carolina. This would prove to be the perfect site for another observation, notes and a sketch of these three galaxies. I saw NGC 474 as round, diffuse and with a brighter nucleus. NGC 470, appeared elongated, diffuse, and twice as large as NGC 474. 

Next, NGC 467 appeared round, faint halo, with a brighter nucleus, and situated a few minutes N of an 8th magnitude star. It was almost the same apparent size as NGC 474. All three galaxies were very easy to locate, relatively bright, and showed excellent contrast.  Again I was bothered concerning the size listing of NGC 474.  My sources indicated that it was the largest of these galaxies, but NGC 470 was clearly the largest in my telescope and in a photo that I had looked at earlier.  Could there be an error in the 7.9” size I read from the NGC 2000 Catalogue, an error which was perpetuated by the other sources? A table of diameters (in arc minutes) from different sources is listed below: 

Source: 

NGC 2000.0:   NGC 470: 3.0  NGC 474: 7.9 

Burnham’s Celestial Handbook:   NGC 470:  1.7 x 1.1   NGC 474:  0.4 x 0.4 

Tom Lorenzin’s 1000+:  NGC 470:  3.2   NGC 474:  8.0 

The Observer’s Guide, Nov/Dec 1991:    NGC 470:  3.0 x 2.0   NGC 474:  7.9 x 7.2 

Deep Sky Field Guide to Uranometria 2000.0:  NGC 470: 3.0 x 1.8   NGC 474: 10.0 x 9.2 

Eicher’s Deep Sky Observing w/Small Telescopes:  NGC 470: 1.7 x 1.1   NGC 474:  0.4 x 0.4 

Astronomy Magazine: January 1993:   NGC 470: 3.0 x 2.0   NGC 474:  7.9 x 7.2 

Luginbuhl & Skiff, Observing Handbook & Catalog:  NGC 470:  3.0 x 2.0   NGC 474:  7.9 x 7.2 

I expressed my concern to Tom English, Professor of Astronomy and Physics at GardnerWebb University, who promptly gathered all available reference material on NGC 474 from his extensive astronomy library at the University. Tom called me on Saturday afternoon, January 7, and invited me to research the data. While I was busy checking each source, Tom was checking the Sky & Telescope Cumulative Index to locate past issues with information on NGC 474. Tom left the lab and returned with a March 1988 issue of Sky & Telescope with a research note on the galaxy and an accompanying photo. 

My quest was about to end: 

On page 244, there was the photo that would resolve the problem. It showed both NGC 470 and NGC 474 overexposed, with a very faint halo surrounding the latter. A quick measurement of each galaxy in the photo showed that, with the halo considered, NGC 474 is indeed about 2 ½ times the size of NGC 470, consistent with the NGC 2000 listings. A closer look at the list of sources gives an indication that this pair has been a source of confusion to many observers. 

It also reveals that cataloged information tends to propagate from one publication to the next. We all use various catalogs for background information (such as size and magnitude) as we set our observing agendas, and too often we do not follow up on this information by making actual measurements ourselves. 

Note that five of the sources listed have the same 3.0 and 7.9 arc minute sizes for NGC 470 and NGC 474, respectively. Burnham and Eicher list identical measurements in their guides as well, but with NGC 470 attributed as the larger galaxy, just as I had noted. In their observing notes, Luginbuhl and Skiff indicate that NGC 470 appears closer to 2’ x 1’, with NGC 474 somewhat smaller. 

In the Nov/Dec issue of The Observer’s Guide, I saw my frustration mirrored in the statement that NGC 474 “is much smaller than its catalog size. Apparently, its outer halo is so faint that it is not visible.” 

Image from: wikisky.org (Note the expanded very faint halo of NGC 474, which cannot be seen visually)

My pencil sketch as following using a 10-inch f/4.5 EQ Newtonian and charcoal on black card stock at the telescope eyepiece.

Roger Ivester 1994

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