Messier Objects

M40: Double Star (Ursa Major) RA: 12h 22.2m / DEC +58° 05'.0
Instrument: 10-inch Starfinder

M40 is a boring double star. I don't mean to dis this object but that's as straightforward a description as there is. The pair are located 1.4 degrees northeast of Megrez, the 3.3 magnitude star placed at the junction between the handle and bowl of the Big Dipper. Fifth magnitude 70 Ursae Majoris is 17' to the southwest.

There is no small amount of controversy surrounding M40. MegaStar, the deep-sky program boasting the largest database of objects, doesn't include this double among the Messier objects. However, the Frenchman clearly observed this double. He measured a position for the stars and included them as the 40th entry in his catalog. My philosophy is if it was good enough for Charles, it's good enough for me.

M40 is also known as Winnecke 4. They are magnitude 10.1 and 9.6 stars separated by 51 arc seconds in right ascension. There is no nebulosity associated with the double but there are a pair of nearby NGC galaxies. One, NGC 4290, caught my eye while make this sketch. It's 16' due west of M40, covers a 3'x1' area and has a visual magnitude of about 11.8. There is no indication from available records that Messier saw this galaxy.

M39 M41


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Revised: October 16, 2002 [WDF]