TEA ON THE MOON :: 60
The Definition

What is φ?

A line divided into two segments where the ratio of the whole to the longer part equals the ratio of the longer to the shorter. This single constraint produces an irrational number of infinite wonder.

The Golden Ratio
1.618034...
φ = (1 + √5) / 2
φ = 1 + 1/φ
φ² = φ + 1
1/φ = φ − 1 = 0.618...
Drag the slider to find the golden ratio
Ratio: 1.000 ← drag toward 61.8%
At the Golden Split

When the slider reaches 61.8%, the ratio of whole-to-larger equals the ratio of larger-to-smaller. That self-similar quality is φ's signature :: it contains itself.

The Spiral

The Golden Spiral

Remove a square from a golden rectangle and the remainder is another golden rectangle. Repeat infinitely. Connect the arcs :: a spiral emerges. Watch it unfurl.

Fibonacci squares: each labeled with its size. Their ratios converge to φ = 1.618...
Step: 0 / 9
Pentagon & φ

Inside Every Face

Every pentagonal face of the dodecahedron contains φ. The diagonal of a regular pentagon is exactly φ times its side length. The intersection of two diagonals divides them at the golden ratio.

Pentagonal φ
diagonal / side = φ
AC / AB = 1.618...

Diagonals intersect at:
AP / AB = φ / φ² = 1 / φ = 0.618...
The Pentagon Star

Each intersection of the five diagonals creates a smaller regular pentagon :: also golden. The pentagram within encodes φ at every junction. Infinitely recursive. :: The same proportion, all the way down. We are inside a fractal.

The Sequence

Fibonacci's Convergence

1, 1, 2, 3, 5, 8, 13, 21, 34, 55... Each term is the sum of the two before it. Divide any term by its predecessor :: the ratio converges to φ.

n Fib(n) Fib(n−1) Ratio
The Pattern

Notice how the ratio column oscillates :: above φ, then below, then above :: each swing narrower than the last. It spirals toward the value, just as the geometric spiral tightens toward its center.

By Fib(12) / Fib(11), we are accurate to 4 decimal places. The Fibonacci sequence does not define φ :: it approaches it. :: The pattern reaches toward its own ideal. We do too.

In Nature

Sunflower seeds pack into 34 and 55 spirals. Pine cones: 8 and 13. Nautilus chambers expand by φ. Leaves around a stem follow Fibonacci fractions of a full rotation. The mathematics is not imposed :: it arises from optimization. :: Form follows φ. Life follows φ. We follow φ.