>Phi is the Golden Mean and has existed at least as long as the Egyptians and the Greeks. No one is sure when it was originally discovered. Phidias studied it and applied it to his sculptures for the Parthenon and Plato considered it to be the key to the physics of the cosmos. Euclid associated it with the construction of a pentagram. It was referred to as the Divine Proportion during the 1500s. Da Vinci provided pictures using it in a paper (actually published by another Italian) about it and most think he may have been the first to refer to it as the Divine Proportion. Johannes Kepler (Keplar's Laws of Planetary Motion concerning elliptical movement of planets) wrote:
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>"Geometry has two great treasures: one is the theorem of Pythagoras; the other, the division of a line into extreme and mean ratio. The first we may compare to a measure of gold; the second we may name a precious jewel."
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>It wasn't referred to as phi until the 1900s when Mark Barr used the Greek letter phi to associate with the dividing a line in the extreme and mean ratio.
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>It is included in the Da Vinci Code book (fiction by the way), but that has nothing to due with its mathematical significance.

Ah, math extracurricular, VI grade, the so-called "golden cross-section", i.e.

a/b=(a+b)/a

where a is the larger section of an interval, and b the smaller. We do find it pleasing to see an image where the ratio between the sides is such, or where the horizon is either at the upper or the lower golden section... but then, it may be because all the major painters and their disciples since ancient Greece have used it, so our whole culture has it, as some sort of a mass-induced Pavlov reflex.

Assigning any mystic properties to geometrical objects is... well, just mysticism. And probably a great way to make money nowadays :).