When should you buy your airline ticket?

A question I've thought about pretty much every time I go to buy a plane ticket. I always thought that the earlier, the better. That's not true according to Cheap Air's graph.

The simple answer is that in 2013 the best time to buy a domestic airline ticket was 54 days in advance, or 7 1/2 weeks on average. But before you send yourself a calendar invite 54 days before your next trip, read on; there is a lot more to the story.