Black lights look like normal lights, but they do something completely different. Switch one on, and fingernails, laundry detergent, highlighters, money and teeth will glow in the dark. Find out what why.
At HowStuffWorks, we're always curious, and 2008 gave us a lot to be curious about -- financial bailouts, skyrocketing food prices and, of course, the Google algorithm. Here are our top 10 questions of the year -- answered. What are yours?