Start with a unit circle, construct its inscribed regular pentagon and extend two non-adjacent sides of this pentagon. The circle through the intersection point and touching to the unit circle, has a circumference of φ × π.
Quite a “golden” circle, thus!

Start with a unit circle, construct its inscribed regular pentagon and extend two non-adjacent sides of this pentagon. The circle through the intersection point and touching to the unit circle, has a circumference of φ × π.

Quite a “golden” circle, thus!