M40 is a double star. M40 is considered to be a mistake in the Messier catalog. There is no nebula or star cluster at this location. This object apparently traces back to object number 1496 in the Prodromus Astronomiae published by Hevelius in 1660. Hevelius described it as a nebula above the back of Ursa Major. In 1764, Charles Messier looked for the nebula above the back of the Great Bear represented by the constellation Ursa Major. However, at the designated position, Messier found only two faint stars. Messier presumed that Hevelius mistook these two stars for a nebula. For some unknown reason, Messier nevertheless included this object in his catalog as M40.
The lower star shown in this image is a magnitude 9.7 star designated as SAO 28353, or alternatively as GSC 3840:1031. The top star shown in this image is a magnitude 10.1 star designated as SAO 28355, or alternatively as GSC 3840:564. The two stars have an angular separation of 53 arc-seconds at a position angle of about 78 degrees. This object is also listed as WNC 4 in the Washington Double Star Catalog. The primary has a spectral type of G0.
This image was taken with an ST-8XE CCD using a Takahashi FCT-150 refractor.
M40 (WDS WNC 4)
Constellation: Ursa Major
RA: 12h 22m 45s Dec: +58d 02' 55"
April 11, 2006
Image by Sid Leach
Scottsdale, Arizona
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