It seems that there is some question as to when to place stars into this category, which, as explained on the category page, is for small groupings of stars that appear to be close to each other but are not known to be physically bound. Up to now, the procedure I've been using is to look in the Washington Double Star Catalog or other catalogs of double and multiple stars (e.g., the Catalog of Components of Double and Multiple Stars) and to use the components given there. (These components are also often mentioned in guides such as Burnham or Jim Kaler's web pages.) This seems to work well enough, so I'd like to suggest that this procedure be recommended on the category page itself. Spacepotato (talk) 02:33, 3 December 2010 (UTC)
Support seems like a good suggestion. 188.8.131.52 (talk) 06:39, 3 December 2010 (UTC)
Comment—I have a concern that this could become a massive, somewhat indiscriminate category because a large number of stars, if not virtually all stars, will have multiple optical neighbors, depending on the cut-off distance. Do we have any idea what percentage of stars this will include?—RJH (talk) 16:15, 3 December 2010 (UTC)
The WDS does not have a fixed cutoff for separation, although most pairs have a separation of 15 arcseconds or less.
The Tycho-2 catalog lists 864,811 stars with a VT magnitude of 11 or lower, compared to the WDS, which lists only 57,616 primaries of pairs with magnitude 11 or lower. (I use 11 as the limit because this is around the completeness limit of the Tycho-2 catalogue.) The fraction of stars which are multiple will decrease with cutoff magnitude, so it will be higher for cutoff magnitudes <11 and lower for cutoff magnitudes >11.
It seems to me that we already have some rather large categories, such as Category:Bayer objects (or, outside of astronomy, Category:1969 births, etc.) So, I think that the primary issue is not category size, but a well-defined inclusion criterion.
Okay. 864,811 multiple star entries would be a massive category indeed.—RJH (talk) 16:37, 7 December 2010 (UTC)
Since there seems to be consensus for it, I'm recommending the procedure outlined above on the category page, and also on Category:Triple stars and Category:Double stars, since the issues there are exactly the same as for this category. Spacepotato (talk) 05:04, 10 December 2010 (UTC)