What do sunflowers, Salvador Dali’s painting “The Sacrament of the Last Supper,” and black holes have in common? They reflect characteristics described by a curious number known since antiquity called the golden ratio, or phi.

This irrational number—which approximates to 1.618 (give or take an endless series of places)—has come to represent the proportions of some ideally pleasing geometrical structures. It has the uncanny propensity of popping up where least expected, applicable to everything from mollusk shells and the crystals of certain unusual materials to the music of Debussy and the architecture of Le Corbusier.

Internationally known astrophysicist Mario Livio leads a fascinating journey as he traces the story of this astonishing number from ancient Egypt and Greece to the present day. Along the way, he introduces historic figures including the followers of Pythagoras and the astronomer Johannes Kepler, and such modern-day thinkers as mathematical physicist Roger Penrose and Dan Shechtman, a 2011 Nobel Prize laureate in chemistry. Livio carefully separates the myth from the math in a way that brings this remarkable number to life.

Livio worked for 24 years with the Hubble Space Telescope and is a best-selling author of popular science books.