NavList:

Antoine, you wrote:
"Just use the Nautical Almanac refraction tables."

Really? For altitudes below zero degrees? Hmm... Not likely using only the Nautical Almanac. One could extrapolate linearly for a quick estimate, but there's no reason to expect much linearity in that range. Or one could try using the little formula from the calculator section in the back of the Nautical Almanac and plug in a negative altitude, but that would be erroneous [the equation is not derived from physical "first principles" and is merely a "fit" to the original refraction tables, and like any such fit, it is invalid outside the original range of argument].

I was hoping you might have corrected your original post by now. Your original here has a link behind the phrase "spectacular sunset", but it fails. If you can find the correct link, please post it in a follow-up, and I will then also fix it in the original post.

Frank Reed