Have a look at this chart and especially the popular science category (if you can just about make it out). While there’s an increase and decrease shadowing the total increase and decrease, that’s not very interesting. Sell twice as many books and you’ll sell (possibly) twice as many pop science books.
But look at 2004. That’s quite a big jump. What happened in 2003 and 2004 that made such a difference? Why did puzzle book sales increase in 2005 too? Well the 2005 increase is probably Soduku. Did Soduku cost pop science sales? The Challenger Disaster was in 2003…did the human face of this trigger increased popular interest in science?