Harold Corwin

NGC 231. John Herschel describes this as "An irregular train of stars and nebulosity in the Nubecula Minor. (Evidently that referred to in Sweep 625 [NGC 220, which see].)" Given this, I think it is very doubtful that John Herschel was seeing just the small cluster which we have taken as his object ever since.

So, bucking tradition, I have used this number to include all of the clusters in the "irregular train", NGC 220, the traditional NGC 222 (but see that for some uncertainty of its own), as well as the small one which has carried the NGC number for many years. I call that little cluster "NGC 231 core" to distinguish it from the overall "irregular train".

By the way, I make the entire size of the "train" roughly 6.5 x 2.5 arcmin. It may extend further northwest and southeast, but this is its obvious size at first glance.

― NGC Notes by Harold Corwin

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