page_title: Twilight
section_title: Definitions and illustrations by illumination
hierarchical_section_title: Twilight / Definitions and illustrations by illumination
caption_attribution_description: English: Long exposure of Dusk in in Landers, California, in the Mojave Desert, USA
context_page_description: Twilight on Earth is the illumination of the lower atmosphere when the Sun is not directly visible because it is below the horizon. Twilight is produced by sunlight scattering in the upper atmosphere, illuminating the lower atmosphere so that Earth's surface is neither completely lit nor completely dark. The word twilight is also used to denote the periods of time when this illumination occurs.
  The lower the Sun is beneath the horizon, the dimmer the twilight. When the Sun reaches 18° below the horizon, the twilight's brightness is nearly zero, and evening twilight becomes nighttime. When the Sun again reaches 18° below the horizon, nighttime becomes morning twilight. Owing to its distinctive quality, primarily the absence of shadows and the appearance of objects silhouetted against the lit sky, twilight has long been popular with photographers, who sometimes refer to it as "sweet light", and painters, who often refer to it as the blue hour, after the French expression l'heure bleue.
  Twilight should not be confused with auroras, which can have a similar appearance in the night sky at high latitudes.
context_section_description: Three subcategories of twilight are established and widely accepted: civil twilight (brightest), nautical twilight, and astronomical twilight (darkest).
caption: Long exposure of nautical twilight in a small town in the Mojave Desert
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