As part of their Earth Month 2013's mission to improve "Understanding and Sustaining Our Home Planet, NASA has waded through the mountainous collection of high resolution digital imagery produced by some of its "fleet of Earth-observing satellites" across many distinct environmental research programs.
Why you ask? I did too, so don't feel bad. It turns out they had the bright idea to combine the individual photos taken by different satellites into something of an animated film using the pictures and ordering them in the proper sequence.
They used this exceptionally clever technique to produce one of the most breathtaking videos I've watched online in a while. You can also check out more on Engadget & Gizmodo if you're not into the whole "brevity" thing.