L’Equation du Temps (The Equation of Time) is an artistic and scientific experiment initiated in 2018 at the Paris Observatory by photographer Raphaël Dallaporta. Conducted jointly with researchers from the Syrte (Système de Références Temps-Espaces) of Paris Observatory, the experiment “Equation of Time” aims to verify the differences between the true solar day, indicated by sundials, and mean solar time, indicated by clocks. While the meridian of true solar time is a straight line, the meridian of mean time has the shape of an elongated figure eight.
Every day, according to an automated protocol, a picture of the Sun is taken at the same time in the Cassini room built in 1671. The accumulation over the year reveals the curve in 8 of the equation of time ∞ represented by the image of the Sun on the Earth.
Each of the first 365 pages of the book is centered on the position of the image of the Sun during its passage at the local mean noon in the Cassini room of Paris Observatory. The data of the shot are specified on each page.