Night flying times

Dave Butler writes:
Stubby wrote:

There is no need for a pilot to actual own a GPS. He can look at a
friend's or one at the FBO, etc. But for the price of an hour of
instruction, anyone can purchase his very own GPS. Or, the FAA could
put up a web page with GPS sunrise and sunset times on it.

AFAIK there is no generally agreed upon "GPS sunrise". I'm guessing each GPS
manufacture has its own proprietary algorithm for determining sunrise/sunset.
That's fine for casual use, but I imagine regulation writers are looking for
something more standard.

And does "rise" mean the first little bit's visible, the
full face is visible, or somewhere in between?