Editing Twilight (section)

{{Short description|Atmospheric illumination by the Sun below the horizon}}
{{other uses}}
[[File:Twilight description full day.svg|thumb|300px|Twilight is the time period between [[dawn]] and [[sunrise]], and between [[sunset]] and [[dusk]].]]
[[File:Twilight-dawn subcategories.svg|thumb|right|300px|[[Morning]] twilight: astronomical, nautical, and civil stages at dawn. The apparent disk of the Sun is shown to scale.<ref name="Low precision formulae">{{cite journal|bibcode=1979ApJS...41..391V|last=Van Flandern |first=T. |author2=K. Pulkkinen |title=Low precision formulae for planetary positions |journal=Astrophysical Journal Supplement Series |volume=31 |issue=3 |year=1980 |page=391 |doi=10.1086/190623 }}</ref>]]
[[File:Twilight subcategories.svg|thumb|right|300px|[[Evening]] twilight: civil, nautical, and astronomical stages at dusk. The solar disk is shown to scale.]]

'''Twilight''' is [[daylight|daylight illumination]] produced by [[diffuse sky radiation]] when the [[Sun]] is below the horizon as sunlight from the upper atmosphere is [[scattering|scattered]] in a way that illuminates both the [[Earth's atmosphere|Earth's lower atmosphere]] and also the Earth's surface. Twilight also may be any period when this illumination occurs, including dawn and dusk.

The lower the Sun is beneath the horizon, the dimmer the sky (other factors such as atmospheric conditions being equal). When the Sun reaches 18° below the horizon, the illumination emanating from the sky is nearly zero, and [[evening]] twilight becomes [[night]]time. When the Sun approaches re-emergence, reaching 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 and painters, who often refer to it as the [[blue hour]], after the [[French language|French]] expression {{lang|fr|l'heure bleue}}.

By analogy with evening twilight, sometimes ''twilight'' is used [[metaphor]]ically to imply that something is losing strength and approaching its end. For example, [[Ageing|very old people]] may be said to be "in the twilight of their lives". The [[collateral adjective]] for ''twilight'' is ''[[crepuscular]]'', which may be used to describe the behavior of animals that are most active during this period.
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