Blue hour
Theblue hour(fromFrenchl'heure bleue;[1][a]pronounced[lœʁblø]) is the period oftwilight(in themorningorevening,around thenautical stage) when theSunis at a significantdepthbelow thehorizon.During this time, the remainingsunlighttakes on a mostly blueshade.This shade differs from the colour of the sky on a clear day, which is caused byRayleigh scattering.
The blue hour occurs when the Sun is far enough below the horizon so that the sunlight's blue wavelengths dominate due to theChappuis absorptioncaused byozone.[2]Since the term iscolloquial,it lacks an official definition such asdawn,dusk,or the three stages of twilight. Rather, blue hour refers to the state ofnatural lightingthat usually occurs around the nautical stage of the twilight period (at dawn or dusk).[3]
The blue hour is shorter in regions near theequatordue to the sun rising and setting at steep angles. In places closer to the poles, the illumination and twilight periods are longer as the sun rises and sets at shallower angles.[4]
Explanation and times of occurrence
[edit]The still commonly presented incorrect explanation claims that Earth's post-sunset and pre-sunrise atmosphere solely receives and disperses the sun's shorter blue wavelengths and scatters the longer, reddish wavelengths to explain why the hue of this hour is so blue.[5]In fact, the blue hour occurs when the Sun is far enough below the horizon so that the sunlight's blue wavelengths dominate due to theChappuis absorptioncaused by ozone.[2]
When theskyis clear, the blue hour can be a colourful spectacle, with theindirect sunlighttinting the sky yellow, orange,red,andblue.This effect is caused by the relativediffusibilityof shorterwavelengths(bluer rays) ofvisible lightversus the longer wavelengths (redder rays).[6]During the blue "hour", red light passes through space while blue light isscatteredin the atmosphere, and thus reaches Earth's surface.
Blue hour usually lasts about 20–96 minutes right after sunset and right before sunrise. Time of year, location, and air quality all have an influence on the exact time of blue hour.[7]For instance in Egypt (every21st of June), whensunsetis at 7:59PM:blue hour occurs from 7:59 PM to 9:35 PM. Whensunriseis at 5:54 AM: blue hour occurs from 4:17 AM to 5:54 AM. Golden hour occurs from 5:54 AM to 6:28 AM and from 7:25 PM to 7:59 PM.
Blue hour in art
[edit]-
Die blaue Stunde(1890), painting byMax Klinger -
Sunset(1897), painting byAntónio Cândido da Cunha -
Twilight(1897), painting byEdmund Tull(Ödön Tull) -
Taj-Mahal, twilight(1920), woodcut byCharles W. Bartlett -
Evening at the Lumber Yards of Kiba(1920), woodcut byKawase Hasui
Blue hour photography
[edit]Many artists value this period for the quality of thesoft light.Although the blue hour does not have an official definition, the blue color spectrum is most prominent when the Sun is between 4° and 8° below the horizon.[6]
Photographers use blue hour for the tranquil mood it sets. When photographing during blue hour it can be favourable to capture subjects that have artificial light sources, such as buildings, monuments, cityscapes, or bridges.
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TheCity of Londonduring the blue hour -
Praia da Ursa,Cabo da Roca,Portugal.A wide-angle view of the seascape during the blue hour -
Zug,Switzerlandduring the blue hour -
Padmanabhaswami Temple of Kerala during the blue hour
See also
[edit]Notes
[edit]- ^A similarcalqueis used in many languages.[citation needed]
References
[edit]- ^Verfaillie, Roland (2011).L'heure Bleue.San Francisco: Purple Onion Press. p. 5.ISBN9780978708559.
- ^abHoeppe, Götz (2007).Why the Sky Is Blue: Discovering the Color of Life.Princeton:Princeton University Press.pp. 249–53.ISBN978-0-691-12453-7.
- ^"The Blue Hour".timeanddate.Retrieved6 April2019.
- ^Wu, Jennifer; Martin, James (13 March 2014).Photography: Night Sky: A Field Guide for Shooting after Dark.Mountaineers Books. p. 139.ISBN978-1-59485-839-0.
- ^"What is the blue hour? Learn about this magic time between daylight and darkness".mnn.Retrieved7 April2019.
- ^ab"Blue Hour – Magic Hour".timeanddate.Retrieved16 October2017.
- ^"What is the blue hour?".earthsky.org.30 August 2014.Retrieved7 April2019.
External links
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