NavList:

Additional information :

(1) : To make my previous post easier to understand, the mention of the elevation "α" of the "local horizon" just means than the Aircraft contrail is exactly sitting there, i.e. grazing the "local horizon" and therefore standing at this same apparent elevation /height angle "α" over the hidden "true horizon". In this entire post I am interested in computing the Aircraft distance to the Observer at the exact time when the Aircraft contrail is disappearing under the local horizon.

I do hope that any interested Reader should probably have construed it this way, but it is better writing it in plain words.

(2) : I observed the contrail on Oct 08th, 2021 by 06:00 UT.

Interestingly enough, just 2 days later and on Oct 10th, 2021 Mr Sun rose up exactly where I saw the Aircraft contrail vanishing behind my local horizon.

Let's go for a LOP then !

From N46°30.222' / W000°47.723', assuming standard conditions at sea level, on Oct 10th, 2021 observe as follows :

06:21:10 UT,  ☼UL = 0°46.8'. Compute Intercept and Azimuth and comment as appropriate.

Again, enjoy

Antoine M. "Kermit" Couëtte