Fred:

Sorry, but I still disagree.

The time of sunset is the point at which the limb of the sun disappears
to an observer. This is an exact legal definition.

I don't think you'd get far in a court of law if a dozen eyewitnesees
said the sun was still visible but you said your mathematical equation
predicted that it had set!

For convenience, we use a mathematical model that uses a constant term
to correct for atmospheric refraction and you can look up those times
in published tables. However, the correction is approximate and
subject to error.

I merely suggested that since the actual time of sunset was not known,
we should allow folks some slack if they land close to sunset to allow
for this error.

The same goes for pressure altitude, by the way.

Mike

Overcast? What's that - I live in Arizona!


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