Andrew Cooper
Nov 22, 2006    Las Cienegas NCA, Pima Co., AZ (map)
46cm f/4.5 Deep Violet

A moderately rich open cluster , large, fairly bright, irregular and clumpy, the main body is strung out a little north-south, with another clump to the west, the nebulosity of IC410 laced through the cluster

Harold Corwin

NGC 1893 is a cluster found by John Herschel. As noted by Brent Archinal in "Star Clusters" and in an email from Wolfgang Steinicke, it is embedded in a large, faint nebulosity found by Max Wolf and listed as IC 410. John Herschel apparently did not see the nebula as he makes no note of it. While Wolf noted stars in his nebula, his note is primarily concerned with the nebula and not the stars.

So, applying the two numbers to both objects is incorrect, though it has been done often in the 20th century catalogues.

Another curiosity here is John Herschel's RA. Steve Gottlieb has found that it is three minutes of time too large (the declination is correct); this carried over into the GC and NGC. I've found that Reinmuth in Die Nebel-Herschel of 1926 flags his position of the cluster as corrected from the NGC, so this may well be the reason that all the current catalogues have the correct RA.

In the sweep (number 51 on 22 January 1827), the minutes of the clock reading is "25::", and the reduced minute of RA is "14:". John Herschel gives no reason for the uncertainty, and he did not carry it over into his 1833 list. So, the GC and NGC appear to have a position with a typical uncertainty, while the actual RA is indeed 3 minutes of time smaller.

I put the center of the cluster a few arcminutes to the northeast of the canonical center near HD 242935. John Herschel's corrected position falls very close to the star, too, so I've adopted Brian's concordant position. That more or less represents the cluster in any case. A detailed study of proper motions with spectroscopy and photometry could sort out the members from the field stars. These could eventually lead to a refined position.

― NGC Notes by Harold Corwin

Drawings, descriptions, and CCD photos are copyright Andrew Cooper unless otherwise noted, no usage without permission.

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