Now, let me tell you the last time that I pulled out a protractor and measured when the sun was 6* below where I could possibly see it. And is defined in the Air Almanac, by the United States Naval Observatory, to be the brightest twilight and that “in good conditions and in the absence of other illumination, is such that the brightest stars are just visible, and terrestrial objects can be easily distinguished.” The period between sunset and when the sun is 6* below the horizon. For the purposes of flight, we really only care about Civil twilight. Civil twilight, nautical twilight, and astronomical twilight. All things being equal, the sky is completely dark when the sun is 18* below the horizon.Īs if this isn’t confusing enough there are three sub-categories of twilight. Or the reverse in the morning, when the sky starts to brighten, but the sun is still below the horizon. Twilight is from the moment the sun is fully below the horizon (sunset) until there is no more sunlight and the sky is completely dark. What is ‘full night’ in this definition? Let’s go one step deeper.
#Dusk definition full
The dictionary definition of twilight is “the light from the sky between full night and sunrise or between sunset and full night produced by diffusion of sunlight through the atmosphere and its dust.”
Let’s break it down to help that understanding. The definition of twilight, and which twilight is important for what purpose, can be confusing to understand. Twilight, and understanding twilight for aviation is important for one reason Night flying.Ĭan you log the hours you flew as night time flight? Are you current in night flight? As we enter the fall / winter months our daylight hours get shorter so pilots start caring about these nuances more.
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