Harold Corwin

IC 2154 = NGC 2139. For once, a problem with an IC object discovered by Lewis Swift is not Swift's problem. His position, already better than average for those objects found by him in 1897, was pinned down by Herbert Howe. So, the identity problem rests with NGC 2139, which see.

To make the longer story short, Dreyer found the trouble in William Herschel's original records of the sweep in which NGC 2139 was discovered. See the NGC object for a bit more.

A curious footnote is Carlson's making this IC object a double star. She gives as her source a Mt. Wilson photograph. The Mt. Wilson observer (Hubble?) was confused somehow as the IC position is spot-on the galaxy.

― IC Notes by Harold Corwin

Harold Corwin

NGC 2139 = IC 2154. Dreyer has a note in his 1912 edition of William Herschel's Scientific Papers on this object. Taken from William Herschel's note in the sweep, it reads "The A.R. cannot be above 10 or 15 s out; the roller went off the apparatus which occasions the uncertainty." The RA is actually 24 seconds out, and the dec, due to another unspecified error, is 8.5 arcmin off. Dreyer was further able to identify a star in the sweep that was closer to the galaxy than William Herschel's "official" reference star, delta Canis Majoris. Comparison with this star led to the correct position.

However, he had not yet done this when Howe and Bigourdan tried to find the NGC object near William Herschel's place -- not surprisingly, neither succeeded. What is surprising is that when Lewis Swift came across the galaxy over a century after William Herschel, he did not make as nearly as large an error in its position as William Herschel. Swift's positions from his last nights in 1897 and 1898 at Lowe Observatory on Echo Mountain are nortoriously bad. But for this object, he actually came within 14 seconds in RA and 1 arcmin in Dec. Herbert Howe pinned the galaxy down with a micrometric observation and it was that position that Dreyer adopted for IC 2154. Dreyer himself discovered the identity when he fixed William Herschel's position for the NGC object.

― NGC Notes by Harold Corwin

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