M 40  (Winnecke 4) -- Double Star (Optical Pair)
Is Winnecke-4 A Messier Object?
Charles Messier (1730-1817) was a comet hunter.  During his life time he was famous
for finding new comets.  Today however, he is known for his list of non-comet like
objects.  Messier kept a list of these objects that looked like comets but were not.  His
purpose for doing so was to ensure that he did not mistake one of these objects for a
comet during future searches.  The Messier list today is usually the first list of deep-sky
objects observed by a new budding amateur astronomer.  Most objects on his list are
of astronomical interest, but a couple mysteries remain about the Messier list.  
Messier 40 is one of them.  Was it truly a mistake Messier would have made?  Is the
double star Winnecke-4, something that Messier really thought might be mistaken for a
comet? It is true, that Messier’s telescope was not of today’s standards, but these two
stars have a large apparent separation of 52”.  Even in my 1960s vintage 60mm
achromatic refractor, Winnecke-4 looks like a double star and is not comet-like at all.  
We probably will never know, beyond a doubt, how this double star came to be M40.  
To add additional injury to M40, it turns out not to be a gravitational double star after all,
but two stars widely separated in space, but just happen to be in the same line-of-sight
from Earth.