Sorry guys, but historically speaking, M102 is exactly the same object as M101. Charles Messier never saw M101 or M102 in his eyepiece, he just copied in the second edition of his famous catalog what his partner Pierre Méchain reported in his observation log. Méchain recognized his own mistake of having logged twice the same object, but it was already too late: the book was published.
Fast forward 200 years or so... Some amateur astronomers started a new flavor of star party called "Messier Marathon", where the goal is to look at all 110 objects if possible in a single night. Instead of having to look twice at M101 (which they would have considered cheating), they decided to replace M102 by a similar galaxy in Draco close to M101 and called it M102.
I have read that story at multiple sources, so I think this is the true story.
Thx
