Re: Time
The problems with sextants that make them impractical for modern air travel are:
1.Speed
Sextants don't tell you where you are, they tell you where you were when you made the observation. There are averaging mechanisms that allow aircraft sextant to partially account for the fact that the aircraft was moving (both vertically and horizontally), but at modern speeds you cover a minute of arc pretty quickly. Radio navigation systems and GPS provide much faster position updates than you could get with a sextant.
2.Complexity of the instrument
Aircraft sextants are precision instruments. They need to be maintained and calibrated or they won't be accurate when you need them, and there are a lot more moving parts to an aircraft bubble sextant than a basic ship's sextant.
3.Complexity of the process
Using a sextant also require an operator (navigator) who knows what they're doing in order to take the sighting and compute the position, compared to radio navigation (VORs, VOR/DME, or GPS). Most pilots don't have any training in using a sextant, so having one would be useless to them.
4.Weather
While the sextant is a reliable instrument the stars are not reliable: They're always there, but sometimes they're not visible. You can't see most of the stars & constellations you would take a sighting of during the day (usually only one star is visible), and clouds can obscure them when you want to take a sighting, delaying or preventing your position fix.
Biting the hand that feeds IT
