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{{short description|Period of twilight in the morning or evening}}
{{short description|Period of twilight in the morning or evening}}
[[File:Sé Catedral de Bragança - Portugal (3663183339).jpg|thumb|Blue hour at the [[Old Cathedral of the Holy Name of Jesus, Bragança]] in Portugal]]
[[File:Sé Catedral de Bragança - Portugal (3663183339).jpg|thumb|Blue hour at the [[Old Cathedral of the Holy Name of Jesus, Bragança]] in Portugal]]
The '''blue hour''' (from [[French language|French]] {{lang|fr|l'heure bleue}};<ref>{{cite book |last=Verfaillie |first=Roland |title=L'heure Bleue |url=https://books.google.com/books?id=P56JAwAAQBAJ&pg=PA5 |page=5 |year=2011 |location=San Francisco |publisher=Purple Onion Press|isbn=9780978708559 }}</ref>{{efn|A similar [[calque]] is used in many languages.{{citation needed|date=March 2017}}}} {{IPA-fr|lœʁ blø|pron}}) is the period of [[twilight]] (in the [[morning]] or [[evening]], around the [[Twilight#Nautical twilight|nautical stage]]) when the [[Sun]] is at a significant [[altitude (astronomy)|depth]] below the [[horizon]]. During this time, the remaining [[sunlight]] takes on a mostly blue [[tints and shades|shade]]. This shade differs from the colour of the sky on a clear day, which is caused by [[Rayleigh scattering]].
The '''blue hour''' (from [[French language|French]] {{lang|fr|l'heure bleue}};<ref>{{cite book |last=Verfaillie |first=Roland |title=L'heure Bleue |url=https://books.google.com/books?id=P56JAwAAQBAJ&pg=PA5 |page=5 |year=2011 |location=San Francisco |publisher=Purple Onion Press|isbn=9780978708559 }}</ref>{{efn|A similar [[calque]] is used in many languages.{{citation needed|date=March 2017}}}} {{IPA|fr|lœʁ blø|pron}}) is the period of [[twilight]] (in the [[morning]] or [[evening]], around the [[Twilight#Nautical twilight|nautical stage]]) when the [[Sun]] is at a significant [[altitude (astronomy)|depth]] below the [[horizon]]. During this time, the remaining [[sunlight]] takes on a mostly blue [[tints and shades|shade]]. This shade differs from the colour of the sky on a clear day, which is caused by [[Rayleigh scattering]].


The blue hour occurs when the Sun is far enough below the horizon so that the sunlight's blue wavelengths dominate due to the [[Chappuis absorption]] caused by [[ozone]].<ref name="Hoeppe">{{cite book |first=Götz |last=Hoeppe |title=Why the Sky Is Blue: Discovering the Color of Life |publisher=[[Princeton University Press]] |location=[[Princeton, New Jersey|Princeton]] |year=2007 |isbn=978-0-691-12453-7 |pages=249–53 |url=https://books.google.com/books?id=-7inyeQbBjQC&pg=PA238}}</ref> Since the term is [[colloquial]], it lacks an official definition such as [[dawn]], [[dusk]], or the three stages of twilight. Rather, blue hour refers to the state of [[diffuse sky radiation|natural lighting]] that usually occurs around the nautical stage of the twilight period (at dawn or dusk).<ref>{{cite web |title=The Blue Hour |url=https://www.timeanddate.com/astronomy/blue-hour.html |publisher=timeanddate.com |access-date=6 April 2019}}
The blue hour occurs when the Sun is far enough below the horizon so that the sunlight's blue wavelengths dominate due to the [[Chappuis absorption]] caused by [[ozone]].<ref name="Hoeppe">{{cite book |first=Götz |last=Hoeppe |title=Why the Sky Is Blue: Discovering the Color of Life |publisher=[[Princeton University Press]] |location=[[Princeton, New Jersey|Princeton]] |year=2007 |isbn=978-0-691-12453-7 |pages=249–53 |url=https://books.google.com/books?id=-7inyeQbBjQC&pg=PA238}}</ref> Since the term is [[colloquial]], it lacks an official definition such as [[dawn]], [[dusk]], or the three stages of twilight. Rather, blue hour refers to the state of [[diffuse sky radiation|natural lighting]] that usually occurs around the nautical stage of the twilight period (at dawn or dusk).<ref>{{cite web |title=The Blue Hour |url=https://www.timeanddate.com/astronomy/blue-hour.html |publisher=timeanddate.com |access-date=6 April 2019}}
</ref>
</ref>


The blue hour is shorter in regions near the [[equator]] due 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.<ref>{{Cite web |date=5 February 2024 |title=Blue Hour: The Most Magical Time of the Day |url=https://ulukayin.org/blue-hour-photography/ |access-date=8 February 2024 |website=ULUKAYIN English}}</ref>
The blue hour is shorter in regions near the [[equator]] due 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.<ref>{{cite book |last1=Wu |first1=Jennifer |last2=Martin |first2=James |title=Photography: Night Sky: A Field Guide for Shooting after Dark |date=13 March 2014 |publisher=Mountaineers Books |isbn=978-1-59485-839-0 |page=139 |url=https://books.google.com/books?id=mS8QAwAAQBAJ&dq=photography+%22blue+hour%22+latitude&pg=PT139 |language=en}}</ref>


==Explanation and times of occurrence==
==Explanation and times of occurrence==
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When the [[sky]] is clear, the blue hour can be a colourful spectacle, with the [[diffuse sky radiation|indirect sunlight]] tinting the sky yellow, orange, [[Belt of Venus|red]], and [[Earth's shadow|blue]]. This effect is caused by the relative [[photon diffusion|diffusibility]] of shorter [[wavelengths]] (bluer rays) of [[visible light]] versus the longer wavelengths (redder rays).<ref name=timeanddate /> During the blue "hour", red light passes through space while blue light is [[scattering|scattered]] in the atmosphere, and thus reaches Earth's surface.
When the [[sky]] is clear, the blue hour can be a colourful spectacle, with the [[diffuse sky radiation|indirect sunlight]] tinting the sky yellow, orange, [[Belt of Venus|red]], and [[Earth's shadow|blue]]. This effect is caused by the relative [[photon diffusion|diffusibility]] of shorter [[wavelengths]] (bluer rays) of [[visible light]] versus the longer wavelengths (redder rays).<ref name=timeanddate /> During the blue "hour", red light passes through space while blue light is [[scattering|scattered]] in 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 impact on the exact timing of blue hour.<ref>{{cite web |title=What is the blue hour? |url=https://earthsky.org/earth/what-is-the-blue-hour |website=earthsky.org |date=30 August 2014 |access-date=7 April 2019}}</ref> For instance in Egypt (every [[Summer solstice|21st of June]]), when [[sunset]] is at 7:59 [[12-hour clock|PM]]: blue hour occurs from 7:59 PM to 9:35 PM. When [[sunrise]] is 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 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.<ref>{{cite web |title=What is the blue hour? |url=https://earthsky.org/earth/what-is-the-blue-hour |website=earthsky.org |date=30 August 2014 |access-date=7 April 2019}}</ref> For instance in Egypt (every [[Summer solstice|21st of June]]), when [[sunset]] is at 7:59 [[12-hour clock|PM]]: blue hour occurs from 7:59 PM to 9:35 PM. When [[sunrise]] is 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.


==Art==
==Blue hour in art==
<gallery>
<gallery>
Max Klinger (1857-1920) l' Heure bleue,1890,huile sur toile 191,5 x 176 cm, Musée des Beaux-Arts de Leipzig.jpg | ''Die blaue Stunde'' (1890), painting by [[Max Klinger]]
Max Klinger (1857-1920) l' Heure bleue,1890,huile sur toile 191,5 x 176 cm, Musée des Beaux-Arts de Leipzig.jpg | ''Die blaue Stunde'' (1890), painting by [[Max Klinger]]
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</gallery>
</gallery>


==Photography==
==Blue hour photography==
Many artists value this period for the quality of the [[hard and soft light|soft 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.<ref name=timeanddate>{{cite web |title=Blue Hour – Magic Hour |url=https://www.timeanddate.com/astronomy/blue-hour.html |publisher=timeanddate.com |access-date=16 October 2017}}</ref>
Many artists value this period for the quality of the [[hard and soft light|soft 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.<ref name=timeanddate>{{cite web |title=Blue Hour – Magic Hour |url=https://www.timeanddate.com/astronomy/blue-hour.html |publisher=timeanddate.com |access-date=16 October 2017}}</ref>


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File:Seascape after sunset denoised.jpg|Praia da Ursa, [[Cabo da Roca]], [[Portugal]]. A wide-angle view of the seascape during the blue hour
File:Seascape after sunset denoised.jpg|Praia da Ursa, [[Cabo da Roca]], [[Portugal]]. A wide-angle view of the seascape during the blue hour
File:CH.ZG.Zug View from Guggi 01 16x9+R 8192x4608 Br058 gp denoising Br075.jpg|[[Zug]], [[Switzerland]] during the blue hour
File:CH.ZG.Zug View from Guggi 01 16x9+R 8192x4608 Br058 gp denoising Br075.jpg|[[Zug]], [[Switzerland]] during the blue hour
Sree Padmanabhaswami Temple of Kerala 3.jpg|Padmanabhaswami Temple of Kerala during the blue hour
</gallery>
</gallery>


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[[Category:Night]]
[[Category:Night]]
[[Category:Atmospheric optical phenomena]]
[[Category:Atmospheric optical phenomena]]
[[Category:Photography]]

Latest revision as of 03:23, 3 October 2024

For other uses, see Blue hour (disambiguation).
Blue hour at the Old Cathedral of the Holy Name of Jesus, Bragança in Portugal

The blue hour (from French l'heure bleue;[1][a] pronounced [lœʁ blø]) is the period of twilight (in the morning or evening, around the nautical stage) when the Sun is at a significant depth below the horizon. During this time, the remaining sunlight takes on a mostly blue shade. This shade differs from the colour of the sky on a clear day, which is caused by Rayleigh scattering.

The blue hour occurs when the Sun is far enough below the horizon so that the sunlight's blue wavelengths dominate due to the Chappuis absorption caused by ozone.[2] Since the term is colloquial, it lacks an official definition such as dawn, dusk, or the three stages of twilight. Rather, blue hour refers to the state of natural lighting that usually occurs around the nautical stage of the twilight period (at dawn or dusk).[3]

The blue hour is shorter in regions near the equator due 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 the Chappuis absorption caused by ozone.[2]

When the sky is clear, the blue hour can be a colourful spectacle, with the indirect sunlight tinting the sky yellow, orange, red, and blue. This effect is caused by the relative diffusibility of shorter wavelengths (bluer rays) of visible light versus the longer wavelengths (redder rays).[6] During the blue "hour", red light passes through space while blue light is scattered in 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 (every 21st of June), when sunset is at 7:59 PM: blue hour occurs from 7:59 PM to 9:35 PM. When sunrise is 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.

Art

[edit]

Photography

[edit]

Many artists value this period for the quality of the soft 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.

See also

[edit]

Notes

[edit]
  1. ^ A similar calque is used in many languages.[citation needed]

References

[edit]
  1. ^ Verfaillie, Roland (2011). L'heure Bleue. San Francisco: Purple Onion Press. p. 5. ISBN 9780978708559.
  2. ^ a b Hoeppe, Götz (2007). Why the Sky Is Blue: Discovering the Color of Life. Princeton: Princeton University Press. pp. 249–53. ISBN 978-0-691-12453-7.
  3. ^ "The Blue Hour". timeanddate.com. Retrieved 6 April 2019.
  4. ^ Wu, Jennifer; Martin, James (13 March 2014). Photography: Night Sky: A Field Guide for Shooting after Dark. Mountaineers Books. p. 139. ISBN 978-1-59485-839-0.
  5. ^ "What is the blue hour? Learn about this magic time between daylight and darkness". mnn.com. Retrieved 7 April 2019.
  6. ^ a b "Blue Hour – Magic Hour". timeanddate.com. Retrieved 16 October 2017.
  7. ^ "What is the blue hour?". earthsky.org. 30 August 2014. Retrieved 7 April 2019.
[edit]
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