Greetings ! I just read Saint's post in the "moving galaxy" thread and though I knew the answer to that, I do not believe I have so far read somewhere an explanation for the existence of the galactic cluster sheets. So, is there a known and recognized reason ? (My guesses : 1. The same reason that star-systems and galaxies are mostly two-dimensional - a simple kinematic solution for a system of bodies enitially spread around mostly at rest and mutually affected by gravitational forces. 2. Some form of quantization during the BB ? ) Thanks. "I sometimes ask myself how it came about that I was the one to develop the theory of relativity. The reason, I think, is that a normal adult never stops to think about problems of space and time. These are things which he has thought about as a child. But my intellectual development was retarded, as a result of which I began to wonder about space and time only when I had already grown up." Albert Einstein Live long and prosper.