Only round craters ?

My son stumped me last night!

He wanted to know why all the craters on the moon appeared round from a direct-on impact and there were no oblong craters from angular trajectories or glancing hits?

Can you point me to an answer to why the craters on the moon appear round?

Or point us to a couple of oblong craters.

Thanks in advance
George P

There are some oblong craters on the moon that are the result of angular impact. Messier and Messier A in Mare Fecunditatis come to mind right off the bat. I am sure that there are many others, but my limited knowledge in selenography prevent me from listing others.

Doug
Midway, FL

When the kinetic energy of an impacting object is converted it is dissipated in all directions thus creating an essentially round crated. The size of the impacted item is typically much smaller that the resulting crater, thus very little signature of the direction of impact is maintained.

I believe Charles Wood covers this issue quite well in The Modern Moon. It takes pretty extraordinary circumstances to make a notably oblong crater.

Schiller is a large and oddly shaped crater;

http://en.wikipedia.org/wiki/Schiller_crater

But I think it's thought to be an odd merger of craters, not an oblong crater per se. I could be wrong.

Messier A and B are the result of some odd sort of collision as well.

http://en.wikipedia.org/wiki/Messier_(crater)

search this page for "Messier" for a good image of the Messier craters...

http://www.anomalous-images.com/clemmoon.html