Why Twilight Can Be a Complicated Time for Pilots

Do you know the difference between civil twilight, nautical twilight and astronomical twilight?

Peter Garrison

Thursday, February 15, 2018 at 08:00 PM ET

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Twilight is partitioned into three zones: civil, nautical and astronomical. Pexels

Key Takeaways:

Night flying, particularly in deep twilight or adverse weather like fog, presents significant hazards due to severely reduced visibility and difficulty identifying ground features or unlit airstrips.
Several fatal accidents underscore poor pilot judgment as a primary factor, including attempting flights into unsuitable conditions, flying illegally, or failing to maintain safe altitudes at night.
Pilots are susceptible to spatial disorientation and visual illusions, such as the "black-hole illusion" during night approaches, which can lead to dangerously low descents even with functional glidepath indicators.

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Twilight is a complicated thing. It is partitioned into three zones. There is civil twilight, which lasts from sunset to when the center of the sun is 6 degrees, or about 12 solar diameters, below the horizon and things can no longer be clearly seen.

Then comes nautical twilight, which ends when the center of the sun is 12 degrees below the horizon and a seaman no longer discerns the break between the western sea and the sky. Finally, astronomical twilight ends when the sun is 18 degrees below the horizon, leaving the sky black enough for the inspection of distant galaxies.