- What's the lowest altitude over the moon where contemporary engineering could comfortably put an artificial satellite into orbit around it? http://whatif.xkcd.com/58/ 50 comments askscience
- XKCD says that if you drive at one third the speed of light, red traffic lights will appear green. Can someone work out what colour the green and yellow traffic lights would be? http://whatif.xkcd.com/14/ 4 comments askscience