Messier A and B
Two of my favorite destinations on the moon are the double craters Messier A and B in Mare Fecunditatis. The impact or impacts (read on) must have happened at very low angles because the rays--twin ejecta blankets--point nearly straight west. The hypothesis has been floated that the two craters were produced by a single impactor diving into the lunar surface and then bouncing back out. I'm no geophysicist but that sounds pretty unlikely. Another hypothesis is that a single impactor hit and bounced. Looks like a pretty short bounce for something traveling many miles per second, and it doesn't explain why the two craters have such similar geometry. Given the number of asteroids that are turning up with moons these days, and the frequency with which comets fall apart, a good ole double impact seems much more plausible to me. But that's just my $0.02.
Anyway, it's a pretty sight in telescopes big and small, and well worth a look if you're out looking up. I took the top photo a year ago today, using a 6" reflector and Nikon Coolpix 4500 digital camera. The photo below was taken this April 1 using the same camera and a 90mm Maksutov Cassegrain at a magnification of only 39x, which goes to show that you don't need a big telescope or high magnification to catch this pair of gems. Click photos to embiggify.