Why is the sky dark at night? You might think the answer is obvious - the sun isn't up! But the only reason the sky looks blue during the day is that sunlight scatters off of the atmosphere -...
JAMES GRIME: Today, we're going to talk about one of the questions that we get sent in a lot at Numberphile, and the question is-- well, Brady, what's the question? BRADY HARAN: The...