Stacy McDermott wrote:
> How Messier thought that people would confuse this with a
> possible comet is a mystery probably never to be solved.
There's not as much as a mystery as you might think.
Messier observed this object to verify an observation made by Johann
Hevelius 100 years earlier. Its inclusion in the Messier list may have
been accidental.
Or, he may have simply wanted to account for all of Hevelius' 16 "nebulous"
objects.
Whatever the case, Messier unambiguously logged a double star, which could
never be mistaken for a comet with a decent scope. However, the double
star that Messier logged is probably not the object that Hevelius observed!
The whole episode is further evidence that the Messier catalog is far from
uniform, both in object coverage and in purpose of inclusion of objects.
http://www.seds.org/messier/m/m040.html
http://www.seds.org/messier/xtra/Bios/hevelius.html
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