The Equation of Time - Aequātiō Diērum

This website is work-in-progress. Please contact the Author with any complaints, corrections, additions or improvements. Thanks to Werner Riegler for extra material and to John Davis, Pete Swanstrom, Frank King, Brain Albinson, Renate & Antonio Palamà, Chris Lusby Taylor, Robert Campbell for extra images, ideas, corrections & permission to publish

.... sundials and watches never seem to tell the same time. Introducing the Equation of Time and its formal definitions.
Solar -v- Civil Mean Time
.... how Solar Time gave way to Local Mean Time, then National Mean Time, and finally Universal Time with Time Zones and Daylight Saving Times, as now used.
The Components of the Equation of Time
.... using videos, the Equation of Time is generated from an astronomical perspective by its two components - the Eccentricity & Obliquity effects.
Mathematically breaking down the Equation
.... how Fourier analysis can be used to break the components of the Equation of Time into manageable trigonometric terms.
Calculating the Equation of Time
.... how the equation of time can be calculated - either using astronomical methods, or by using Fourier-derived terms.
The Equation of Time in Astronomy & Navigation
.... other than sundials and clocks, where else is the Equation of Time used.
Displaying the Equation of Time
... the many ways in which the Equation of Time can be visualised - particularly on sundials.
Equation of Time Nomograms
.... describes two nomograms (slide rules) that give the Equation of Time.
Variation in the Equation of Time
.... the equation of time varies in the long term. For the pedant, there are many astronomical effects that - in microscopic terms - perturb its value.
Ptolemy's ‘Invention’ of the Equation of Time
.... introduces the Greek astronomer, Ptolemy, together with his great work the Almagest. ... how he predicted the Equation of Time. ... why his work lasted for some 1400 years.
EoT Incidentals
.... a few tit-bits about the Equation of Time ... earliest sunrise and sunset ... a gnomonic riddle ... planetary analemmas.
Back to Top