crepuscule

Crepuscule is the term for twilight, the period between day and night when the sky remains illuminated even though the sun is below the horizon. Although rooted in French, the word appears in English contexts as a literary loanword used to evoke a mood of transition, ambiguity, and liminality. Its etymology traces to the Latin crepusculum, passing through Old French before entering modern languages.

In modern discourse, twilight is divided by solar angle into three parts. Civil twilight occurs when the sun is between 0 and 6 degrees below the horizon and enough light remains for outdoor activity. Nautical twilight spans from 6 to 12 degrees below the horizon, with the horizon still visible at sea. Astronomical twilight covers 12 to 18 degrees below the horizon, after which the sky is considered properly dark for most astronomical observations. These stages influence lighting, visibility, and the perception of the landscape.

Twilight can produce distinctive visual effects, such as crepuscular rays, where sunlight streams through gaps in clouds or terrain, creating apparent shafts of light. In biology, the related term crepuscular describes animals that are most active during dawn and dusk, including many mammals, birds, and insects.

In culture, crepuscule is used in literature, music, and visual art to signal transition and mood. It often appears in titles and descriptions that emphasize the boundary between day and night, or the moment of change itself.