On Apr 19, 8:14*pm, brian whatcott wrote:
Darryl Ramm wrote:
/snip/
One of the problems we've seen is that there is really no such thing
as an "official" sunset time, just times calculated from astronomical
tables/snip/
Mike

It may be semantics but the problem some pilots run into is there is
*exactly* a precise definition of sunset time, it's just too bad it
might be different from what they observe */snip/
Darryl

I have run into a definition of sunset that used to go like this:
"The time at which the trajectory of the Solar center is six degrees
below the local horizon."

You can see how this could vary when the horizon is the Rockies, versus
five miles West where it might be 5000 ft lower...

Brian W

Stop tying to make this hard, there is one proper definition to worry
about for gliding in the USA. That is the table generated by the US
Naval Observatory. The FARs define sunset times as published in the
Air Alamanac which is produced by the US Naval Observatory, but for
practical purposes the official data is the USNO tables I provided the
link to. Those tables are exactly what is used for badge and records
flights in the USA and are the numbers glider pilots need to worry
about (unless the glider is one of the few equipped with lights and
appropriate certification, etc. to fly until the end of civil
twilight, in which case the USNO has civil twilight tables as well).

Darryl