Today’s Nasty Mathematics Challenge: Watch this video (taken by astronauts on the International Space Station with a camera that picks up low-intensity light, and then edited by Michael König, and sped up), and estimage the number of light bulbs whose light is visible:
[vimeo]32001208[/vimeo]
HINT: The task is easier (but not much) if you enlarge the video to watch it full-screen.