M40: The “Unknown” Messier Object
May 2010 :
What is the most most-observed deep-sky object in the Messier Catalog? Some might suggest the Orion Nebula (M42) or Andromeda Galaxy (M31), both cosmic showpieces. More likely, it’s the Pleiades (M45), a striking and easily observed naked eye cluster.
What about the other end of the spectrum – those Messier objects that receive scant attention? The least-observed might well be Messier 40. Arguably the oddest member of the Catalog, M40 isn’t a cluster, nebula, or galaxy. It’s a double star! We might well label M40 “Messier’s Mistake.”
Messier stumbled upon this stellar duo while searching for a nebulous object reported to be in the area. For some reason, perhaps because it might appear nebulous at low power or in an inferior instrument, he added it to his Catalog. A century later, another comet hunter, Friedrich Auguste Theodor Winnecke, rediscovered the object. He correctly catalogued it as a double star, and it bears the alternate identity Winnecke 4. Finding M40 isn’t a problem. Start at delta (?) Ursae Majoris, then move about a degree northeast to 70 UMa. In the same low-power field a quarter degree further northeastward is M40. As double stars go, M40 isn’t a very inspirational sight. Its magnitude 9.7 and 10.1 component stars are separated by over 52 arc-seconds. Quite likely, it’s an optical pair. It may not be one of the night sky’s spectacles, but the path to observing all of the Messier objects goes through M40.
Your comments on this column are welcome. E-mail me at gchaple@hotmail.com
.
