Sé Catedral de Bragança - Portugal (3663183339)

The blue hour (from French ; ) is the period of

twilight 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. The word twilight can also refer to the periods of time when this il ...

(in the

morning Morning is the period from sunrise to noon. There are no exact times for when morning begins (also true of evening and night) because it can vary according to one's lifestyle and the hours of daylight at each time of year. However, morning strict ...

evening Evening is the period of a day that starts at the end of the afternoon and overlaps with the beginning of night. The exact times when evening begins and ends depend on location, time of year, and culture, but it is generally regarded as beginn ...

, around the nautical stage) when the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

is at a significant depth below the

horizon The horizon is the apparent line that separates the surface of a celestial body from its sky when viewed from the perspective of an observer on or near the surface of the relevant body. This line divides all viewing directions based on whether i ...

. During this time, the remaining

sunlight Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light. On Earth, sunlight is scattered and filtered through Earth's atmosphere, and is obvious as daylight when t ...

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 Rayleigh scattering ( ), named after the 19th-century British physicist Lord Rayleigh (John William Strutt), is the predominantly elastic scattering of light or other electromagnetic radiation by particles much smaller than the wavelength of the ...

. 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 Chappuis absorption () refers to the absorption of electromagnetic radiation by ozone, which is especially noticeable in the ozone layer, which absorbs a small part of sunlight in the visible portion of the electromagnetic spectrum. The Chappu ...

caused by

ozone Ozone (), or trioxygen, is an inorganic molecule with the chemical formula . It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope , breaking down in the lo ...

. Since the term is

colloquial Colloquialism (), also called colloquial language, everyday language or general parlance, is the linguistic style used for casual (informal) communication. It is the most common functional style of speech, the idiom normally employed in conver ...

, it lacks an official definition such as

dawn Dawn is the time that marks the beginning of twilight before sunrise. It is recognized by the appearance of indirect sunlight being scattered in Earth's atmosphere, when the centre of the Sun's disc has reached 18° below the observer's horizo ...

dusk 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, enou ...

, or the three stages of twilight. Rather, blue hour refers to the state of

natural lighting Daylighting is the practice of placing windows, skylights, other openings, and reflective surfaces so that sunlight (direct or indirect) can provide effective internal lighting. Particular attention is given to daylighting while designing a bui ...

that usually occurs around the nautical stage of the twilight period (at dawn or dusk).

Explanation and times of occurrence

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. 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

caused by ozone. When the

sky The sky is an unobstructed view upward from the surface of the Earth. It includes the atmosphere and outer space. It may also be considered a place between the ground and outer space, thus distinct from outer space. In the field of astronomy, ...

is clear, the blue hour can be a colourful spectacle, with the indirect sunlight tinting the sky yellow, orange,

red Red is the color at the long wavelength end of the visible spectrum of light, next to orange and opposite violet. It has a dominant wavelength of approximately 625–740 nanometres. It is a primary color in the RGB color model and a secondar ...

, and

blue Blue is one of the three primary colours in the RYB colour model (traditional colour theory), as well as in the RGB (additive) colour model. It lies between violet and cyan on the spectrum of visible light. The eye perceives blue when obs ...

. This effect is caused by the relative diffusibility of shorter

wavelengths In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tro ...

(bluer rays) of

visible light Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 te ...

versus the longer wavelengths (redder rays). 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 20–30 minutes right after sunset and right before sunrise. For instance, if the sun sets at 6:30 p.m., blue hour would occur from 6:40 p.m. to 7 p.m.. If the sun were to rise at 7:30 a.m., blue hour would occur from 7 a.m. to 7:20 a.m.. Time of year, location, and air quality all have an impact on the exact timing of blue hour.

Blue hour in art

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 (18 February 1857 – 5 July 1920) was a German artist who produced significant work in painting, sculpture, prints and graphics, as well as writing a treatise articulating his ideas on art and the role of graphic arts and printmak ...

Pôr-do-Sol (1897) - António Cândido da Cunha.png , ''Sunset'' (1897), painting by António Cândido da Cunha Tull-Twilight.jpg , ''Twilight'' (1897), painting by Edmund Tull (Ödön Tull) Taj-Mahal, twilight - CWB (monogram) ; Charles W. Bartlett. LCCN2018646015.jpg , ''Taj-Mahal, twilight'' (1920), woodcut by

Charles W. Bartlett Charles William Bartlett (1 June 186016 April 1940) was an English painter and printmaker who settled in Hawaii. Biography Bartlett studied metallurgy and worked in that field for several years. At age 23, he enrolled in the Royal Aca ...

Tōkyō jūnidai, Kiba no yūgure by Kawase Hasui.jpg , ''Evening at the Lumber Yards of Kiba'' (1920), woodcut by

Kawase Hasui was an artist, one of modern Japan's most important and prolific printmakers. He was a prominent designer of the '' shin-hanga'' ("new prints") movement, whose artists depicted traditional subjects with a style influenced by Western art. Like ma ...

Blue hour photography

Super moon over City of London from Tate Modern 2018-01-31 4

Many artists value this period for the quality of the

soft light Hard and soft light are different types of lighting that are commonly used in photography and filmmaking. Soft light is light that tends to "wrap" around objects, projecting diffused shadows with soft edges, whereas hard light is more focused and ...

. 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. 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.

Notes

References

External links