So I am in the midst of telescope fixes because I fried the motor drive on my EQM-35 GOTO mount due to a grease freeze that locked up my DEC axis during a slew.  After much work, I finally have a replacement on the way.  In the meantime, though, I started a project to convert my excellent Takahashi EM-100 GEM to have ST-4 guiding capability (but not GOTO, darn it).  Thanks to Doug Anderson of Shoestring Astronomy, I was able to get the circuit diagram and parts listing for a possible method.  It was a little scary to be soldering on electronics in the mount controller, but I built a circuit board with the necessary relays and an RJ12 connector and wired the whole thing to the controller in the right places (I hope).  I went out two nights ago with my trusty Astrophysics 5" APO refractor on the mount  for a trial run to see if the autoguiding would work.  The good news is that PHD2 linked to the ST-4 guiding and finished a calibration cycle in good fashion, followed by indicating that it was in guiding mode.  The bad news is that my computer went flaky on me due to low available memory and SharpCap was unable to save any images -- they all got dropped.  As a result, I couldn't keep any images to examine carefully after the session to see if the stars were staying nicely round over 3 to 4 minute exposures.  By the time I had floundered around getting to this point, it was pretty late (the dogs start having nervous breakdowns if I'm not in bed by 11:00, an impediment to my astrophotography) so I made a decision on the fly to image the moon.  I set SharpCap up for 2 minute videos and hit start capture; the stupid computer dropped frames, but at least not all of them.  I got about 160 frames each  from four videos and stacked about 50 % of those.  The refractor is really good for the moon and the seeing was unusually steady on this evening and I was able to get a pretty good result with a rather small sample (320 or so frames).  I hadn't imaged the moon in a long time, so it was a fun adventure.

In examining the image my eye caught an unusual feature in Mare Fecunditatis:  Two light, straight streaks, approximately 170 km in length, emanate westward from a double craterlet (Messier and Messier A) and appear to be ejecta of some kind.  I've highlighted the feature in the closeup in the revision.  A little research led me to find that some observers call these streaks the comet's tail on the moon.  A really good reference I found (cited below) offers a theory for what happened in the creation of the "comet's tail."  A possible scenario is that an asteroid hit the moon from the east at an angle of less than 5 degrees.  At such a low impact angle, it easily could have skipped and fragmented such that a second impact due to a fragment took place very close to the first impact.  The first crater, Messier, is decidedly elongated, which is consistent with a low angle impact.  The second crater, Messier A, is the source of the ejecta that formed the rays that look sort of like a comet's tail.  It appears as if the impact that created Messier A was into an elevated area and it is easy to imagine that this kind of impact could have produced the ejecta.  Crazy ...


https://www.astroshop.eu/magazine/practical-tips/observation/a-moonwalk/strange-happenings-in-the-mare-fecunditatis/i,1291