The Equation of Time – a real example.
Here is a photo of a sundial at Abingdon School taken at 15:23BST on 11 October 2021:
The shadow shows the time as approximately 2:29 which is not the same as clock time.
Correction 1 – adjust for BST so 2:29+1 hr = 3:29
Correction 2 – the equation of time shows that for 11 October, which is Day 284 of the year, a sundial will be approximately 12 minutes fast. This means the clock should read 12 minutes earlier which is 3:17
Correction 3 – the longitude of Abingdon is 1.288 degrees west and the Earth takes 4 minutes to turn every 1 degree so 4 x 1.288 = 5.152 minutes. This must be added to the sundial time as it is a westerly longitude, giving the final, corrected time as approximately 3:22 compared to the actual clock time of 3:23.