Harold Corwin

NGC 222, though usually taken as a smaller, fainter cluster northeast of NGC 220 (which see), may in fact be a fourth observation of NGC 220 itself. The other three observations are from Sweeps 482, 625=626 (see my comment about this sweep in the note for NGC 220), and 745. These have reasonably accordant positions and descriptions.

NGC 222, on the other hand, was picked up in a single sweep (441 on 11 March 1834), and -- if it is NGC 220 -- has a discordant position (all these positions are given in the big table). John Herschel notes that this sweep was "below the pole" in the descriptions of several other objects including NGC 242, 248, 294, 346, and 371. Some of these are also noted as having uncertain positions in the sweep which adds to my own uncertainty about the observation of NGC 222.

John Herschel made its position 3-4 seconds east and 4 arcmin south of NGC 220. His description reads simply "vF, R, outlying". I suspect the "outlying" refers to its position in the SMC.

The faint cluster, ESO 029-SC004, usually carrying the number "NGC 222" is 14 seconds of time east and 1.1 arcminutes north of NGC 220, not a good match at all for John Herschel's object. That position, and the fact that John Herschel did not record NGC 220 in Sweep 442, leads to my skepticism in accepting the faint cluster as a genuine discovery by John Herschel. So, I've put my usual question marks on the numbers in question.

See Archinal and Hynes for a similar discussion, though they eventually accept the modern identification.

Jenni Kay, in her "A Visual Atlas of the Magellanic Clouds" also accepts the modern identification of NGC 222, but without question. Using an 8-inch Schmit-Cassegrain telescope at 110X, she found it "small, round, faint" and "noticeably fainter [than] its neighbour NGC 220."

In May 2016, I re-reduced John Herschel's observation from the sweep, using the previous object in the sweep, HD 3719, as a reference star. There is no mistake in John Herschel's own reduction, but I wondered if a wire error might be possible. He has wire "2" recorded in the sweep. If he, in fact, used wire "1", then the RA of NGC 222 would be 00 38 31 (J2000) -- there is nothing in that RA at his recorded declination (-73 27.9; J2000). If he had actually recorded the object leaving the field, the RA would be 00 44 01 (also J2000); this position lands about 2.4 arcminutes southeast of NGC 242 = NGC 241 (which see for problems of its own). However, NGC 242 is the next object in Sweep 441, so it is not NGC 222.

John Herschel has a curious note at the end of the sweep: "[Vision?] bad objects faint and much light cut off by tree tops (to be cut away)". There is another line at the bottom of the page, but it is mostly illegible in the high-contrast Herschel Archive reproduction. The "tree tops" comment is fascinating, though John Herschel notes in CGH under his entry for NGC 242 in this sweep, "(in a sweep below the pole and ill-seen) the RA is probably also in error."

All of this reinforces the idea that NGC 222 is actually a fourth observation of NGC 220. So, I've replaced the question mark on this possibility with a colon, raising the identity to a probability, if not a certainty.

― NGC Notes by Harold Corwin

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