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.


The issue is not atmospheric refraction.

The issue is not the definition of sunset.

The issue is the defintion of _time_ of sunset.

If the "time of sunset' is defined by a mathematical model,
then the time of sunset is independent of the actual atmospheric
conditions and therefor does not vary with them.

That was my point, and I am sorry that I was unclear.

The issue at hand was what time should be used to determine
if a pilot has landed befor sunset. OP's complaint was that
'time of sunset' was highly uncertain. My point is that it is
only highly uncertain if you use an entirely impractical
definiton of 'time of sunset'.

As an astronomer who knows a sunset when he sees one,
how do you know the sun has set when the sky is overcast?

--

FF