Actually, got this from Digg, with the title "The Only Known Public Photograph Of A P-G Cloud On A Rocket" -- that's a Prandlt-Glauert Singularity, fool. Not like I knew. Anyway, it's a cloud that appears around when something breaks the sound barrier, but it doesn't occur BECAUSE it breaks the sound barrier, contrary to popular misconception.
Click and expand for a big-ass version.
You can get the "non-technical" explanation here. Personally, though, I'd say if that's the non-technical explanation -- geez. Anyway, thought it was a great picture for the 4th, as the only known picture of a rocket piercing a P-G cloud as it breaks the sound barrier and then goes on to take a "small step for Mankind" on the moon. Good shot, which I just color corrected. Funny that no one did that after all these years. Pic had a blueish sheen to it.