A vocabulary of landscape — a landscape of words
1083 entries
twilight
Twilight is the light in the sky when the sun is below the horizon, produced by sunlight scattering through the upper atmosphere. It is divided into three stages by how far down the sun has gone: civil twilight, when you can still work outside; nautical, when the horizon is still visible against the sky and a sextant will work; and astronomical, after which the sky is as dark as it will get.
Etymology
The word is Old English and the twi- is the same element as in twin and twice, meaning two. What it meant is argued over: either the half-light, light at half strength, or the light between two things, meaning between day and night. Both readings are old.
Notes
The stages are defined at six, twelve, and eighteen degrees of the sun below the horizon. Above roughly sixty degrees of latitude, astronomical twilight never fully ends around midsummer, so the sky does not reach true darkness for weeks at a time. English has an unusual number of words for this hour and the site carries gloaming, cockshut, dimpsy, owl light, crepuscule, and nightfall, each taking a different angle on it.