Blue is the colour between violet and green on the optical spectrum of visible light.
Color or colour is the characteristic of human visual perception described through color categories, with names such as red, blue, yellow, green, orange, or purple.
Light is electromagnetic radiation within a certain portion of the electromagnetic spectrum.
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Human eyes perceive blue when observing light with a wavelength between 450 and 495 nanometres, which is between 45 and 49.5 Ångströms.
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats, and thus the inverse of the spatial frequency.
The nanometre or nanometer is a unit of length in the metric system, equal to one billionth of a metre.
The ångström or angstrom is a unit of length equal to 10−10 m or 0.1 nanometre.
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Blues with a higher frequency and thus a shorter wavelength gradually look more violet, while those with a lower frequency and a longer wavelength gradually appear more green.
In painting and traditional colour theory, blue is one of the three primary colours of pigments, along with red and yellow, which can be mixed to form a wide gamut of colours.
A set of primary colors is, most tangibly, a set of real physical pigmented media or colored lights that can be combined in varying amounts to produce a "gamut" of colors.
In the visual arts, color theory or colour theory is a body of practical guidance to color mixing and the visual effects of a specific color combination.
In color reproduction, including computer graphics and photography, the gamut, or color gamut, is a certain complete subset of colors.
Blue is also a primary colour in the RGB colour model, used to create all the colours on the screen of a television or computer monitor.
The RGB color model is an additive color model in which red, green and blue light are added together in various ways to reproduce a broad array of colors.
The modern English word blue comes from Middle English bleu or blewe, from the Old French bleu, a word of Germanic origin related to Old Dutch, Old High German, Old Saxon blāo and Old Frisian blāw, blau.
Middle English is collectively the varieties of the English language spoken after the Norman Conquest until the late 15th century; scholarly opinion varies but the Oxford English Dictionary specifies the period of 1150 to 1500.
In linguistics, Old Dutch or Old Low Franconian is the set of Franconian dialects spoken in the Low Countries during the Early Middle Ages, from around the 5th to the 12th century.
Modern English is the form of the English language spoken since the Great Vowel Shift in England, which began in the late 14th century and was completed in roughly 1550.
The clear sky and the deep sea appear blue because of an optical effect known as Rayleigh scattering.
Scattering is a general physical process where some forms of radiation, such as light, sound, or moving particles, are forced to deviate from a straight trajectory by one or more paths due to localized non-uniformities in the medium through which they pass.
Rayleigh scattering, named after the British physicist Lord Rayleigh, is the elastic scattering of light or other electromagnetic radiation by particles much smaller than the wavelength of the radiation.
When sunlight passes through the atmosphere, the blue wavelengths are scattered more widely by the oxygen and nitrogen molecules, and more blue comes to our eyes.
An atmosphere is a layer of gases surrounding a planet or other material body, that is held in place by the gravity of that body.
Oxygen is a chemical element with symbol O and atomic number 8.
Rayleigh scattering also explains blue eyes; there is no blue pigment in blue eyes.
Eye color is a polygenic phenotypic character determined by two distinct factors: the pigmentation of the eye's iris and the frequency-dependence of the scattering of light by the turbid medium in the stroma of the iris.
Distant objects appear more blue because of another optical effect called atmospheric perspective.
Aerial perspective or atmospheric perspective refers to the effect the atmosphere has on the appearance of an object as it is viewed from a distance.
Blue has been used for art and decoration since ancient times.
The semi-precious stone lapis lazuli, coming from mines in Afghanistan, was used in ancient Egypt for jewelry and ornament and later, in The Renaissance, to make the pigment ultramarine, the most expensive of all pigments.
The Renaissance was a period in European history, from the 14th to the 17th century, regarded as the cultural bridge between the Middle Ages and modern history.
Lapis lazuli, or lapis for short, is a deep blue metamorphic rock used as a semi-precious stone that has been prized since antiquity for its intense color.
Afghanistan, officially the Islamic Republic of Afghanistan, is a landlocked country located within South Asia and Central Asia.
In the Middle Ages, cobalt blue was used to colour the stained glass windows of cathedrals.
A cathedral is a Christian church which contains the seat of a bishop, thus serving as the central church of a diocese, conference, or episcopate.
The term stained glass can refer to coloured glass as a material or to works created from it.
Cobalt blue is a blue pigment made by sintering cobalt oxide with alumina at 1200 °C.
Beginning in the 9th century, Chinese artists used cobalt to make fine blue and white porcelain.
"Blue and white pottery" covers a wide range of white pottery and porcelain decorated under the glaze with a blue pigment, generally cobalt oxide.
Porcelain is a ceramic material made by heating materials, generally including kaolin, in a kiln to temperatures between 1,200 and 1,400 °C.
Blue dyes for clothing were made from woad in Europe and indigo in Asia and Africa.
Isatis tinctoria, also called woad, dyer's woad, or glastum, is a flowering plant in the family Brassicaceae.
Indigo is a deep and rich color close to the color wheel blue, as well as to some variants of ultramarine.
A dye is a colored substance that has an affinity to the substrate to which it is being applied.
In 1828 a synthetic ultramarine pigment was developed, and synthetic blue dyes and pigments gradually replaced mineral pigments and vegetable dyes.
Pierre-Auguste Renoir, Vincent van Gogh and other late 19th century painters used ultramarine and cobalt blue not just to depict nature, but to create moods and emotions.
Pierre-Auguste Renoir, commonly known as Auguste Renoir, was a French artist who was a leading painter in the development of the Impressionist style.
Vincent Willem van Gogh was a Dutch Post-Impressionist painter who is among the most famous and influential figures in the history of Western art.
In the late 18th century and 19th century, blue became a popular colour for military uniforms and police uniforms.
A military uniform is the standardised dress worn by members of the armed forces and paramilitaries of various nations.