Mrs Wales==at St Peters is only ever rostered -- jotter

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Date Posted: 06:22:33 12/22/09 Tue
Author: on a Sunday===no other day
Subject: Mrs Wales==at St Peters is only ever rostered
In reply to: Yellow Red Blue Primary colours 's message, "Options trader founder of Wikipedia has personal appeal on" on 06:20:26 12/22/09 Tue

>Please read:
>A personal appeal from
>Wikipedia founder Jimmy Wales [Hide][Show]Wikipedia
>Forever Our shared knowledge. Our shared treasure.
>Help us protect it. [Show]Wikipedia Forever Our
>shared knowledge. Our shared treasure. Help us protect
>it. Visible spectrum
>From Wikipedia, the free encyclopedia
>Jump to: navigation, search
>"Visible light" redirects here. For other uses, see
>Visible light (disambiguation).
>
>White light dispersed by a prism into the colors of
>the optical spectrum.The visible spectrum is the
>portion of the electromagnetic spectrum that is
>visible to (can be detected by) the human eye.
>Electromagnetic radiation in this range of wavelengths
>is called visible light or simply light. A typical
>human eye will respond to wavelengths from about 380
>to 750 nm.[1] In terms of frequency, this corresponds
>to a band in the vicinity of 790–400 terahertz. A
>light-adapted eye generally has its maximum
>sensitivity at around 555 nm (540 THz), in the green
>region of the optical spectrum (see: luminosity
>function). The spectrum does not, however, contain all
>the colors that the human eyes and brain can
>distinguish. Unsaturated colors such as pink, or
>purple variations such as magenta, are absent, for
>example, because they can only be made by a mix of
>multiple wavelengths.
>
>Visible wavelengths also pass through the "optical
>window", the region of the electromagnetic spectrum
>that passes largely unattenuated through the Earth's
>atmosphere. Clean air scatters blue light more than
>wavelengths toward the red, which is why the mid-day
>sky appears blue. The human eye's response is defined
>by subjective testing (see CIE), but atmospheric
>windows are defined by physical measurement.
>
>The "visible window" is so called because it overlaps
>the human visible response spectrum. The near infrared
>(NIR) windows lie just out of human response window,
>and the Medium Wavelength IR (MWIR) and Long
>Wavelength or Far Infrared (LWIR or FIR) are far
>beyond the human response region.
>
>Many species can see wavelengths that fall outside the
>"visible spectrum". Bees and many other insects can
>see light in the ultraviolet, which helps them find
>nectar in flowers. Plant species that depend on insect
>pollination may owe reproductive success to their
>appearance in ultraviolet light, rather than how
>colorful they appear to us. Birds too can see into the
>ultraviolet (300-400 nm), and some have sex-dependent
>markings on their plumage, which are only visible in
>the ultraviolet range.[2][3]
>
>Contents [hide]
>1 History
>2 Spectral colors
>3 Spectroscopy
>4 Color display spectrum
>5 See also
>6 References
>
>
>[edit] History
>
>Newton's color circle, from Opticks of 1704, showing
>the colors correlated with musical notes. The spectral
>colors from red to violet are divided by the notes of
>the musical scale, starting at D. The circle completes
>a full octave, from D to D. Newton's circle places
>red, at one end of the spectrum, next to violet, at
>the other. This reflects the fact that non-spectral
>purple colors are observed when red and violet light
>are mixed.Two of the earliest explanations of the
>optical spectrum came from Isaac Newton, when he wrote
>his Opticks, and from Goethe, in his Theory of
>Colours, although earlier observations had been made
>by Roger Bacon who first recognized the visible
>spectrum in a glass of water, four centuries before
>Newton discovered that prisms could disassemble and
>reassemble white light.[4]
>
>Newton first used the word spectrum (Latin for
>"appearance" or "apparition") in print in 1671 in
>describing his experiments in optics. Newton observed
>that when a narrow beam of sunlight strikes the face
>of a glass prism at an angle, some is reflected and
>some of the beam passes into and through the glass,
>emerging as different colored bands. Newton
>hypothesized that light was made up of "corpuscles"
>(particles) of different colors, and that the
>different colors of light moved at different speeds in
>transparent matter, with red light moving more quickly
>in glass than violet. The result is that red light
>bends (refracted) less sharply than violet as it
>passes through the prism, creating a spectrum of
>colors.
>
>Newton divided the spectrum into seven named colors:
>red, orange, yellow, green, blue, indigo, and violet.
>(Some schoolchildren memorize this order using the
>mnemonic ROY G. BIV.) He chose seven colors out of a
>belief, derived from the ancient Greek sophists, that
>there was a connection between the colors, the musical
>notes, the known objects in the solar system, and the
>days of the week.[5][6] The human eye is relatively
>insensitive to indigo's frequencies, and some
>otherwise well-sighted people cannot distinguish
>indigo from blue and violet. For this reason some
>commentators, including Isaac Asimov, have suggested
>that indigo should not be regarded as a color in its
>own right but merely as a shade of blue or violet.
>
>Johann Wolfgang von Goethe argued that the continuous
>spectrum was a compound phenomenon. Where Newton
>narrowed the beam of light to isolate the phenomenon,
>Goethe observed that a wider aperture produces not a
>spectrum, but rather reddish-yellow and blue-cyan
>edges with white between them. The spectrum only
>appears when these edges are close enough to overlap.
>
>In the early 19th century, the concept of the visible
>spectrum became more definite, as light outside the
>visible range—ultraviolet and infrared—was discovered
>and characterized by William Herschel, Johann Wilhelm
>Ritter, Thomas Young, Thomas Johann Seebeck, and
>others.[7] Young was the first to measure the
>wavelengths of different colors of light, in 1802.[8]
>
>The connection between the visible spectrum and color
>vision was explored by Thomas Young and Hermann von
>Helmholtz in the early 19th century. Their theory of
>color vision correctly proposed that the eye uses
>three distinct receptors to perceive color.
>
>[edit] Spectral colors
>
>Color Wavelength Frequency
>violet 380–450 nm 668–789 THz
>blue 450–495 nm 606–668 THz
>green 495–570 nm 526–606 THz
>yellow 570–590 nm 508–526 THz
>orange 590–620 nm 484–508 THz
>red 620–750 nm 400–484 THz
>Colors that can be produced by visible light of a
>single wavelength (monochromatic light) are referred
>to as the pure spectral colors.
>
>Although the spectrum is continuous, with no clear
>boundaries between one color and the next, the ranges
>may be used as an approximation.[9]
>
>[edit] Spectroscopy
>
>Rough plot of Earth's atmospheric transmittance (or
>opacity) to various wavelengths of electromagnetic
>radiation, including visible light.Spectroscopy is the
>study of objects based on the spectrum of color they
>emit or absorb. Spectroscopy is an important
>investigative tool in astronomy where scientists use
>it to analyze the properties of distant objects.
>Typically, astronomical spectroscopy uses
>high-dispersion diffraction gratings to observe
>spectra at very high spectral resolutions. Helium was
>first detected by analyzing the spectrum of the Sun.
>Chemical elements can be detected in astronomical
>objects by emission lines and absorption lines. The
>shifting of spectral lines can be used to measure the
>red shift or blue shift of distant or fast-moving
>objects. The first exoplanets were discovered by
>analyzing the Doppler shift of stars at a resolution
>that revealed variations in radial velocity as small
>as a few meters per second. The presence of planets
>was revealed by their gravitational influence on the
>motion of the stars.
>
>[edit] Color display spectrum
>Color displays (e.g., computer monitors and
>televisions) mix red, green, and blue color to create
>colors within their respective color triangles, and so
>can only approximately represent spectral colors,
>which are in general outside any color triangle.

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