Epoch J2000.0 Equinox J2000.0
|Right ascension||12h 22m 12.5s|
|Declination||+58° 4' 59"|
|Apparent magnitude (V)||9.65 + 10.10|
Winnecke 4 (also known as Messier 40 or WNC 4) is a double star in the constellation Ursa Major. It was discovered by Charles Messier in 1764 while he was searching for a nebula that had been reported in the area by Johannes Hevelius. Not seeing any nebulae, Messier catalogued this double star instead. It was subsequently rediscovered by Friedrich August Theodor Winnecke in 1863, and included in the Winnecke Catalogue of Double Stars as number 4. Burnham calls M40 "one of the few real mistakes in the Messier catalog," faulting Messier for including it when all he saw was a double star, not a nebula of any sort.
In 1991 the separation between the components was measured at 51.7", an increase since Messier's time. Data gathered by astronomers Brian Skiff (2001) and Richard L. Nugent (2002) strongly suggest that this is merely an optical double star rather than a physically connected system.
The nearby nebula observed by Hevelius may have been the nearby ring galaxy NGC 4290. The galaxy, being 12th magnitude, may have been bright enough to notice for large telescopes at the time, but not quite bright enough for Messier.
In 2016, by using parallax measurements from the Gaia satellite, it was definitively proven that the two stars comprising the double star (HD 238107 and HD 238108) are entirely unrelated, confirming the previous suggestion by Skiff and Nugent.
- Burnham's Celestial Handbook, "Ursa Major: M40", p. 1982
- "Messier 40". SEDS Messier Database. Retrieved 13 March 2013.
- Merrifield, Gray, Haran. "Gaia Shows That Messier 40 is Definitely Not a Binary Star". arXiv. Retrieved 5 December 2016.
- SEDS: Messier Object 40
- Messier 40 CCD LRGB image with 2 hrs total exposure
- Sir Patrick Moore; Mike Merrifield; Pete Lawrence. "M40 – Optical Double Star". Deep Sky Videos. Brady Haran.
- Winnecke 4 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images