civil dawn) and EECT (end evening civil twilight, i.e. In the United States' military, the initialisms BMCT (begin morning civil twilight, i.e. Ĭivil twilight is the period when enough natural light remains that artificial light in towns and cities is not needed. Midtown Manhattan during civil twilight, demonstrating blue hourĬivil twilight is defined as when the geometric center of the Sun is between 6° below the horizon and the horizon itself. For other uses, see Civil twilight (disambiguation). The collateral adjective for twilight is crepuscular, which may be used to describe the behavior of animals that are most active during this period. For example, very old people may be said to be "in the twilight of their lives". 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 and painters, who often refer to it as the blue hour, after the French expression l'heure bleue.īy analogy with evening twilight, the word twilight is also sometimes used metaphorically, to imply that something is losing strength and approaching its end.
When the Sun again reaches 18° below the horizon, nighttime becomes morning twilight. When the Sun reaches 18° below the horizon, the twilight's brightness is nearly zero, and evening twilight becomes nighttime. The lower the Sun is beneath the horizon, the dimmer the twilight (other factors such as atmospheric conditions being equal). The word twilight can also refer to the periods of time when this illumination occurs. Twilight is light produced by sunlight scattering in the upper atmosphere, when the Sun is below the horizon, which illuminates the lower atmosphere and the Earth's surface. Evening twilight: civil, nautical, and astronomical stages at dusk.
The apparent disk of the Sun is shown to scale. Morning twilight: astronomical, nautical, and civil stages at dawn. Twilight is the time period between dawn and sunrise, or between sunset and dusk. For other uses, see Twilight (disambiguation).
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