Harold Corwin

NGC 867 may be the same galaxy as NGC 875. Or it may be the same as IC 225. Or it may be neither, or another galaxy altogether. I don't have enough information to tell. Here is the story.

This is the second of William Herschel's third class (very faint) of nebulae, found during his first season of sweeping the sky. He placed it "13 minutes :: following, -- north" of 60 Ceti. Dreyer has a note in the Scientific Papers that reads (in full):

Sweep 61, Dec 21, 1783. "An almost invisible F. neb., it is R. and about 8 or 10 arcsec diameter, being brighter in the center than outwards. It can only be seen when the glass is perfectly clean and the attention confined to the object." By two diagrams, it is about 1 1/2 deg nf a star which was taken to be 69 Ceti, but obs. was interrupted by clouds. Not found by Bigourdan twice.

In his 1912 MN list of corrections to William Herschel's NGC nebulae, Dreyer shortens this to read merely, "The place of III.2 is extremely uncertain."

The suggestion that it might be NGC 875 comes from d'A who found N875 and measured a pretty accurate position for it. Dreyer copied this suggestion into the NGC description for N875. Auwers, in his reduction of William Herschel's nebulae places N867 at "02 07 29, -1::" for 1830 which places it at 02 13 37, -0.5 for 1950. This is more than a degree south of the GC (and NGC) position, and I wonder if Auwers has his declination sign wrong. He has no note for the object, nor does John Herschel in GC.

And that is pretty much it as far as the observations go. The crude offset from 60 Ceti suggests that N875 is the galaxy William Herschel saw, while the 69 Ceti note suggests that IC 225 might be his object. NGC 875 is brighter by half a magnitude and is therefore the more obvious choice, but the agreement of the diagrams -- assuming the identification of the star as 69 Ceti is correct -- is also compelling.

We will have to go back to William Herschel's observing records for the sweep to look for other clues. For example, I suspect that Dreyer has replaced the original offset published in PT, but that is only a suspicion, based on John Herschel's adoption of a fully-reduced position in GC, and on Auwers's partially-reduced position.

So, at the moment, all I can say is "NGC 867 may be the same galaxy as NGC 875. Or it may be the same as IC 225. Or ..."

I find Dreyer's note in the Scientific Papers a bit curious. Caroline Herschel's fair copy of the Sweep says only "A nebula eF, R, 8 or 10[arcsec] d, bM. 60 Ceti f 13[min] PD about 89[deg] 53[arcmin]. For description see F[ixt] St[ars], Vol. 5, page 476". Dreyer apparently copied that description into his note.

The curiosity comes because Caroline Herschel has clearly written "60 [sixty] Ceti", not 69 [sixty nine] Ceti". Though that star, whichever one it is, is the only star in the sweep, it's clock correction agrees reasonably well with the only other star with a similar correction from the same night, 55 Piscium in the previous sweep: -5h 37m 02.9s for 60 Ceti, and -5h 29m 39.8s for 55 Piscium. Had the star been 69 Ceti, the correction would have been -5h 18m 17.7s. The difference of nearly 20 minutes with 55 Psc compared with just 7.4 minutes makes the identity of 60 Ceti more likely in my mind, though the other is certainly possible.

So, I come back again to NGC 875. That fits William Herschel's description, and while I am not going to change the question mark on the identification, I think the meager evidence leads us to this galaxy as William Herschel's object from his early sweep. The position I give in the table, by the way, is Caroline Herschel's 1800 position (02 05 37, 89 58 [NPD]) precessed to J2000. It is clearly very uncertain with the RA given to a full minute of time, and the NPD merely estimated.

― NGC Notes by Harold Corwin

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