Daylength at altitude summer

[owenc]

How would a flight during the Northern Summer months experience darkness? Northern British Isles have a sun angle of no lower than 12 degrees below the horizon.

Does this mean that the flight would be at dusk throughout the night? Or would it to be pitch dark at 12 degrees below the horizon?

[nonsense]

The distance to the horizon, d, in nautical miles, can be calculated from the height of the observer, h, in feet, by the approximation (https://en.wikipedia.org/wiki/Horizon#Approximate_geometrical_formulas) d = squareroot (h).
At 32,400 feet, this gives 180 nautical miles or 3 degrees of latitude (https://astronavigationdemystified.com/the-relationships-between-longitude-and-latitude-and-the-nautical-mile/) to the horizon.

The arctic circle lies at a latitude of about 66.5 degrees north.

If the sun is 12 degrees below the horizon at midnight (eg: midsummer at 54.5 degrees north, say the Lake District), then at an altitude of 32,400 feet, the sun is just 9 degrees below the horizon*.

Consider the different defined twilights (https://www.timeanddate.com/astronomy/different-types-twilight.html):
Civil twilight, sun 6 degrees below horizon
Nautical twilight, sun 12 degrees below horizon
Astronomical twilight, sun 18 degrees below horizon

Astronomical twilight probably equates to your concept of "pitch dark", so you can see that in mid summer, Windemere won't be pitch dark at ground level, and will be "somewhat lighter" at typical airliner altitude.


*With back of an envelope accuracy.

[owenc]

Thanks! Just working out for my flight tonight to see how bright it will be.