Where is the sunset time measured from?
Question
You just said the sun is going to set at 8:21, but where is that going to be? Where do they measure that from?
Jane, North Finchley
Answer
** Definitive **
Name: Peter, Dulwich
Qualification: I used to navigate a ship for the Royal Navy
Answer: It depends on a few things, the simplest of which is the sun crosses the meridien - due south - at a different altitude each day and during the summer, it crosses higher. The earth turns 15 degrees each hour, so the sun will advance to the west at hour angles and you can work out how many hour angles it will take for the sun to move from your meridien to the horizon and the angle is reduced to zero. And then that tells you what time the sun sets.
** Double definitive **
Name: Dave, Loughton
Qualification: Putting flesh upon the bones
Answer: Sunset is when the sun is six degrees above the horizon. Zero degrees is actually evening twilight.