Mike the Strike wrote:
Fred:

You should really check your facts before posting twaddle!

Clearly I should have said to ask any physicist or astronomer who is
conversant with atmospheric refraction, which you clearly are not.
Because of variations in refraction, sunset (the time when the limb of
the sun becomes invisible to an observer) may vary by several minutes
from that calculated by the accepted formula. This formula assumes a
constant refraction that is unlikely to be exact for any specific place
or time.


Mike

This is like the advice from the old joke about the guys who get lost
in a balloon, then ask someone on the ground where they are, and the
person on the ground tells them they are up in the air in a balloon.
The joke is that the person on the ground must be a lawyer, beacuse his
answer was technicaly correct, but totally useless.

Same goes for actual sunset. Unless you are on a ship at sea, you won't
have a clear level horizon to observe actual sunset. So the refraction
issue is moot. And if you wait until you observe actual sunset in
flight, the sun will have already set on the ground.

The predicted sunset time is the only thing relevant for flight
planning.