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:

Fatal aviation accidents often stem from poor pilot judgment, particularly when flying at night or in challenging low-light and adverse weather conditions like dense fog.
The article details incidents where pilots crashed after attempting flights to unlighted airstrips in pitch darkness or flying dangerously low in unclear conditions, resulting in collisions with trees.
One accident highlights the danger of spatial disorientation, such as the "black-hole illusion," which can lead pilots to unknowingly descend below a safe glidepath during a night landing approach, even with navigational aids present.

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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.