I should specify - it seems that the black blocks can't be hit until all other blocks are gone, but sometimes they can, or at least one can (normally by a sniper), is this just a glitch or am I missing something?
Literally no skill required, but fun, and a good way to explain constellations and relative positioning to people.
Others are commenting on the Lennon at 45, it was the Einstein towards the end that made it for me :)