Dusk occurs at the darkest stage of twilight, or at the very end of astronomical twilight after sunset and just before nightfall.[ The Random House College Dictionary, "dusk".] At predusk, during early to intermediate stages of twilight, enough light in the sky under clear conditions may occur to read outdoors without artificial lighting; however, at the end of civil twilight (when Earth rotates to a point at which the center of the Sun's disk is 6° below the local horizon), such lighting is required to read outside.
Technical definitions
The time of dusk is the moment at the very end of astronomical twilight, just before the minimum brightness of the
night sky sets in, or may be thought of as
the darkest part of evening twilight.
However, technically, the three stages of dusk are as follows:
-
At civil dusk, the center of the Sun's disc goes 6° below the horizon in the evening. It marks the end of civil twilight, which begins at sunset. At this time objects are still distinguishable and depending on weather conditions some stars and planets may start to become visible to the naked eye. The sky has many colors at this time, such as orange and red. Beyond this point artificial light may be needed to carry out outdoor activities, depending on atmospheric conditions and location.
-
At nautical dusk, the Sun moves to 12° below the horizon in the evening. It marks the end of nautical twilight, which begins at civil dusk. At this time, objects are less distinguishable, and stars and planets appear to brighten.
-
At astronomical dusk, the Sun's position is 18° below the horizon in the evening. It marks the end of astronomical twilight, which begins at nautical dusk. After this time the Sun no longer illuminates the sky, and thus no longer interferes with astronomical observations.
Gallery
File:Scots pine at dusk, Ridley Plain, New Forest - geograph.org.uk - 296737.jpg|Scots pine at early dusk in New Forest, England
File:Dusk at the shore, Silverdale - geograph.org.uk - 5042036.jpg|Dusk at the shore
File:Eastwards at dusk from Dalvanie - geograph.org.uk - 3406039.jpg|Looking eastwards at dusk
File:Sandakan at dusk (10498416104).jpg|Sandakan, Malaysia at dusk
File:Beached boats on the Fleet at dusk - geograph.org.uk - 2537423.jpg|Beached boats at dusk
File:Jardim Botânico, Curitiba (20240301 185956).jpg|Curitiba at dusk, Brazil
File:Singapore Marina Bay Dusk 2018-02-27.jpg|Nautical dusk in Marina Bay, Singapore
File:Dusk-A330.JPG|Astronomical twilight as seen from a plane window
See also
