A vocabulary of landscape — a landscape of words
1054 entries
blue hour
The stretch of twilight, before sunrise and after sunset, when the sun is well below the horizon and the sky holds a deep saturated blue rather than fading straight to black. It is not a full hour and it is not the same length twice; near the equator, it is brief, and at high latitudes in summer it can run most of the night. Artificial light and skylight balance during it, which is why cities photograph best then.
Etymology
A translation of French l’heure bleue, in use among French painters and writers before photographers took it over. Blue itself came into English from Old French bleu, from a Germanic root, displacing the native Old English hǣwen — one of the odder facts about English color words, that the French form pushed out the English one for a color the English could see perfectly well.
Notes
The blue is not simply leftover daylight. With the sun below the horizon, the light reaching you has taken a long slant through the ozone layer, and ozone absorbs strongly in the orange and red through what is called the Chappuis band.