We found this article in Cretive Bloq about the famous Golden Ratio. They explain it in very simple terms!

“There’s a common mathematical ratio found in nature that can be used to create pleasing, natural looking compositions in your design work. We call it the Golden Ratio, although it’s also known as the Golden Mean, The Golden Section, or the Greek letter Phi.”

The article: Guide to the Golden Ratio | Graphic design | Creative Bloq.

Another great analysis can be found in this article: The Parthenon and Phi, the Golden Ratio

Picure: http://pamphotography.wordpress.com/2011/08/06/the-golden-ratio-phi-and-photography/