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.
For a year, the artist has taken a daily picture of the sun entering the Cassini Room at midday every day, as close as possible to the eyecup located 9.933 m south of the meridian. 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.
About the equation of time
The equation of time is a notion that reflects the inequalities of solar time. The notion of “mean solar time” refers to an ideal and fictitious time, where the sun returns in the same direction after 24 hours. Every day when the sun is visible, the sun passes at the observatory meridian, in this Cassini room. We then see this spot of light that crosses the Paris meridian at solar noon.
About the book
Each of the 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.
Conceived as a playful Flip Book object, the reader can see the curve forming over the pages. At the end of the book, Denis Savoie, scientific advisor and associate researcher at SYRTHE, explains the principles of the equation of time.
Equation of Time is designed by Kummer & Herrman and published by The Eyes Publishing in collaboration with Picto Fondation in the framework of the 2019 Niepce Prize.
About the author
Raphaël Dallaporta, French artist-photographer, will present his project Mesures du Monde at the Equation of Time conference with Denis Savoie, astronomer and specialist in the history of science. It is a project conceived from the notion of measurement and around the principle of the equation of time.
VIDEO INTERVIEW // Raphaël Dallaporta & Denis Savoie (in French)
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