MadSci Network: Chemistry |
You've got the answer already -- it's not the temperature, it's that the sunlight is more direct in the summer than in the winter. To prove that, you can do an experiment. At around noon one day, put the paper on something that you can tilt toward the sun. Cover half of it with a piece of cardboard. Tilt it up so it's facing as close to straight at the sun as you can get it, and leave it for an hour or two. The next day, take the cardboard off the covered side and put it over the side that was exposed. Now, put it back in the sun, but this time don't tilt it up. Leave it for about the same length of time as the first day. When you take it in, and have both sides uncovered, you'll see that the side exposed when tilted up faded more than the other side! This will work best with dark colors, because they fade more.
Try the links in the MadSci Library for more information on Chemistry.