Fibonacci spiral

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The Fibonacci spiral (which is NOT a true logarithmic spiral) approximates the Golden spiral (which IS a true logarithmic spiral). It is made up of a series of quarter-circular arcs whose radii are consecutively increasing Fibonacci numbers. Every quarter turn a Fibonacci spiral gets wider not by 

ϕ

, but by a changing factor that equals the ratio of a term in the Fibonacci sequence to its predecessor. The ratios of consecutive terms in the Fibonacci series approach 

ϕ

, the Golden ratio, so that the two spirals are very similar in appearance.