Winnecke 4
Winnecke 4 is an optical double star consisting of two unrelated stars in the constellation Ursa Major.
WNC 4 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 and Richard L. Nugent strongly suggested that this was merely an optical double star rather than a physically connected system. In 2016, parallax measurements from the Gaia satellite showed that the two stars involved are unrelated, confirming the previous suggestion by Skiff and Nugent. As measured by Gaia, the two stars are 350±30 pc and 140±5 pc distant, so one is over twice as far as the other.
