A report on Sun and Light

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A triangular prism dispersing a beam of white light. The longer wavelengths (red) and the shorter wavelengths (blue) are separated.
Illustration of the Sun's structure, in false color for contrast
The electromagnetic spectrum, with the visible portion highlighted
Illustration of a proton-proton reaction chain, from hydrogen forming deuterium, helium-3, and regular helium-4.
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Illustration of different stars's internal structure, the Sun in the middle has an inner radiating zone and an outer convective zone.
Beam of sun light inside the cavity of Rocca ill'Abissu at Fondachelli-Fantina, Sicily
High-resolution image of the Sun's surface taken by the Daniel K. Inouye Solar Telescope (DKIST)
Due to refraction, the straw dipped in water appears bent and the ruler scale compressed when viewed from a shallow angle.
During a total solar eclipse, the solar corona can be seen with the naked eye, during the brief period of totality.
Hong Kong illuminated by colourful artificial lighting.
The Sun's transition region taken by Hinode's Solar Optical Telescope
Pierre Gassendi.
Sunlight and glare seen overlooking from the International Space Station
Christiaan Huygens.
Once outside the Sun's surface, neutrinos and photons travel at the speed of light
Thomas Young's sketch of a double-slit experiment showing diffraction. Young's experiments supported the theory that light consists of waves.
Visible light photograph of sunspot
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Measurements from 2005 of solar cycle variation during the previous 30 years
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The size of the current Sun (now in the main sequence) compared to its estimated size during its red-giant phase in the future
The Solar System, with sizes of the Sun and planets to scale. The terrestrial planets are on the right, the gas and ice giants are on the left.
The Trundholm sun chariot pulled by a horse is a sculpture believed to be illustrating an important part of Nordic Bronze Age mythology.
Sol, the Sun, from a 1550 edition of Guido Bonatti's Liber astronomiae.
False-color image taken in 2010 as seen in 30.4-nanometer ultraviolet light wavelength
A false-color of a coronal hole on the Sun forming a question mark (22 December 2017)
A false-color solar prominence erupts in August 2012, as captured by the Solar Dynamics Observatory
The Sun seen from Earth, with glare from the lenses. The eye also see glare when looked towards the Sun directly.
Sun and Immortal Birds Gold Ornament by ancient Shu people. The center is a sun pattern with twelve points around which four birds fly in the same counterclockwise direction, Shang dynasty

It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy mainly as light, ultraviolet, and infrared radiation.

- Sun

The main source of natural light on Earth is the Sun.

- Light
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7 related topics with Alpha

Overall

A pseudocolor image of two people taken in long-wavelength infrared (body-temperature thermal) radiation.

Infrared

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A pseudocolor image of two people taken in long-wavelength infrared (body-temperature thermal) radiation.
This false-color infrared space telescope image has blue, green and red corresponding to 3.4, 4.6, and 12 μm wavelengths, respectively.
Plot of atmospheric transmittance in part of the infrared region
Materials with higher emissivity appear closer to their true temperature than materials that reflect more of their different-temperature surroundings. In this thermal image, the more reflective ceramic cylinder, reflecting the cooler surroundings, appears to be colder than its cubic container (made of more emissive silicon carbide), while in fact, they have the same temperature.
Active-infrared night vision: the camera illuminates the scene at infrared wavelengths invisible to the human eye. Despite a dark back-lit scene, active-infrared night vision delivers identifying details, as seen on the display monitor.
Thermography helped to determine the temperature profile of the Space Shuttle thermal protection system during re-entry.
Hyperspectral thermal infrared emission measurement, an outdoor scan in winter conditions, ambient temperature −15 °C, image produced with a Specim LWIR hyperspectral imager. Relative radiance spectra from various targets in the image are shown with arrows. The infrared spectra of the different objects such as the watch clasp have clearly distinctive characteristics. The contrast level indicates the temperature of the object.
Infrared light from the LED of a remote control as recorded by a digital camera
Reflected light photograph in various infrared spectra to illustrate the appearance as the wavelength of light changes.
Infrared hair dryer for hair salons, c. 2010s
IR satellite picture of cumulonimbus clouds over the Great Plains of the United States.
The greenhouse effect with molecules of methane, water, and carbon dioxide re-radiating solar heat
Beta Pictoris with its planet Beta Pictoris b, the light-blue dot off-center, as seen in infrared. It combines two images, the inner disc is at 3.6 μm.
An infrared reflectogram of Mona Lisa by Leonardo da Vinci
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Thermographic image of a snake eating a mouse
Infrared radiation was discovered in 1800 by William Herschel.
Infrared hair dryer for hair salons, c. 2010s

Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light.

Slightly more than half of the energy from the Sun was eventually found, through Herschel's studies, to arrive on Earth in the form of infrared.

Levels of ozone at various altitudes (DU/km) and blocking of different bands of ultraviolet radiation: In essence, all UVC is blocked by diatomic oxygen (100–200 nm) or by ozone (triatomic oxygen) (200–280 nm) in the atmosphere. The ozone layer then blocks most UVB. Meanwhile, UVA is hardly affected by ozone, and most of it reaches the ground. UVA makes up almost all UV light that penetrates the Earth's atmosphere.

Ultraviolet

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Levels of ozone at various altitudes (DU/km) and blocking of different bands of ultraviolet radiation: In essence, all UVC is blocked by diatomic oxygen (100–200 nm) or by ozone (triatomic oxygen) (200–280 nm) in the atmosphere. The ozone layer then blocks most UVB. Meanwhile, UVA is hardly affected by ozone, and most of it reaches the ground. UVA makes up almost all UV light that penetrates the Earth's atmosphere.
A 380 nanometer UV LED makes some common household items fluoresce.
Ultraviolet photons harm the DNA molecules of living organisms in different ways. In one common damage event, adjacent thymine bases bond with each other, instead of across the "ladder". This "thymine dimer" makes a bulge, and the distorted DNA molecule does not function properly.
Sunburn effect (as measured by the UV index) is the product of the sunlight spectrum (radiation intensity) and the erythemal action spectrum (skin sensitivity) across the range of UV wavelengths. Sunburn production per milliwatt of radiation intensity is increased by nearly a factor of 100 between the near UV‑B wavelengths of 315–295 nm
Demonstration of the effect of sunscreen. The man's face has sunscreen on his right side only. The left image is a regular photograph of his face; the right image is of reflected UV light. The side of the face with sunscreen is darker because the sunscreen absorbs the UV light.
Signs are often used to warn of the hazard of strong UV sources.
UV damaged polypropylene rope (left) and new rope (right)
IR spectrum showing carbonyl absorption due to UV degradation of polyethylene
A portrait taken using only UV light between the wavelengths of 335 and 365 nanometers.
Aurora at Jupiter's north pole as seen in ultraviolet light by the Hubble Space Telescope.
A bird appears on many Visa credit cards when they are held under a UV light source
After a training exercise involving fake body fluids, a healthcare worker's personal protective equipment is checked with ultraviolet light to find invisible drops of fluids. These fluids could contain deadly viruses or other contamination.
A collection of mineral samples brilliantly fluorescing at various wavelengths as seen while being irradiated by UV light.
Effects of UV on finished surfaces in 0, 20 and 43 hours.
A low-pressure mercury vapor discharge tube floods the inside of a hood with shortwave UV light when not in use, sterilizing microbiological contaminants from irradiated surfaces.
Entomologist using a UV light for collecting beetles in Chaco, Paraguay.

Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays.

The Sun emits ultraviolet radiation at all wavelengths, including the extreme ultraviolet where it crosses into X-rays at 10 nm.

The electromagnetic spectrum

Electromagnetic spectrum

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Range of frequencies of electromagnetic radiation and their respective wavelengths and photon energies.

Range of frequencies of electromagnetic radiation and their respective wavelengths and photon energies.

The electromagnetic spectrum
A diagram of the electromagnetic spectrum, showing various properties across the range of frequencies and wavelengths
Plot of Earth's atmospheric opacity to various wavelengths of electromagnetic radiation. This is the surface-to-space opacity, the atmosphere is transparent to longwave radio transmissions within the troposphere but opaque to space due to the ionosphere.
Plot of atmospheric opacity for terrestrial to terrestrial transmission showing the molecules responsible for some of the resonances
The amount of penetration of UV relative to altitude in Earth's ozone

This frequency range is divided into separate bands, and the electromagnetic waves within each frequency band are called by different names; beginning at the low frequency (long wavelength) end of the spectrum these are: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays at the high-frequency (short wavelength) end.

The Sun emits its peak power in the visible region, although integrating the entire emission power spectrum through all wavelengths shows that the Sun emits slightly more infrared than visible light.

The Sun, as seen from low Earth orbit overlooking the International Space Station. This sunlight is not filtered by the lower atmosphere, which blocks much of the solar spectrum.

Sunlight

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The Sun, as seen from low Earth orbit overlooking the International Space Station. This sunlight is not filtered by the lower atmosphere, which blocks much of the solar spectrum.
Sunrise over the Gulf of Mexico and Florida. Taken on 20 October 1968 from Apollo 7.
Sunlight on Mars is dimmer than on Earth. This photo of a Martian sunset was imaged by Mars Pathfinder.
Solar irradiance spectrum at top of atmosphere, on a linear scale and plotted against wavenumber
Sunlight shining through clouds, giving rise to crepuscular rays
Spectrum of the visible wavelengths at approximately sea level; illumination by direct sunlight compared with direct sunlight scattered by cloud cover and with indirect sunlight by varying degrees of cloud cover. The yellow line shows the power spectrum of direct sunlight under optimal conditions. To aid comparison, the other illumination conditions are scaled by the factor shown in the key so they match at about 470 nm (blue light).
Sunlight penetrating through a forest canopy in Germany
Édouard Manet: Le déjeuner sur l'herbe (1862-63)
Téli verőfény ("Winter Sunshine") by László Mednyánszky, early 20th century
Sun bathers in Finland

Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light.

When direct solar radiation is not blocked by clouds, it is experienced as sunshine, a combination of bright light and radiant heat.

White light is dispersed by a prism into the colors of the visible spectrum.

Visible spectrum

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Portion of the electromagnetic spectrum that is visible to the human eye.

Portion of the electromagnetic spectrum that is visible to the human eye.

White light is dispersed by a prism into the colors of the visible spectrum.
Laser beams with visible spectrum
Newton's color circle, from Opticks of 1704, showing the colors he associated 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.
Newton's observation of prismatic colors (David Brewster 1855)
How visible light interacts with objects to make them colorful
Approximation of spectral colors on a display results in somewhat distorted chromaticity
Earth's atmosphere partially or totally blocks some wavelengths of electromagnetic radiation, but in visible light it is mostly transparent

Electromagnetic radiation in this range of wavelengths is called visible light or simply light.

For example, Helium was first detected by analysis of the spectrum of the sun.

Illustration of the relative abilities of three different types of ionizing radiation to penetrate solid matter. Typical alpha particles (α) are stopped by a sheet of paper, while beta particles (β) are stopped by an aluminum plate. Gamma radiation (γ) is dampened when it penetrates lead. Note caveats in the text about this simplified diagram.

Radiation

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Often categorized as either ionizing or non-ionizing depending on the energy of the radiated particles.

Often categorized as either ionizing or non-ionizing depending on the energy of the radiated particles.

Illustration of the relative abilities of three different types of ionizing radiation to penetrate solid matter. Typical alpha particles (α) are stopped by a sheet of paper, while beta particles (β) are stopped by an aluminum plate. Gamma radiation (γ) is dampened when it penetrates lead. Note caveats in the text about this simplified diagram.
The international symbol for types and levels of ionizing radiation (radioactivity) that are unsafe for unshielded humans. Radiation, in general, exists throughout nature, such as in light and sound.
Some kinds of ionizing radiation can be detected in a cloud chamber.
Graphic showing relationships between radioactivity and detected ionizing radiation
Gamma radiation detected in an isopropanol cloud chamber.
Alpha particle detected in an isopropanol cloud chamber
Electrons (beta radiation) detected in an isopropanol cloud chamber
The electromagnetic spectrum
In electromagnetic radiation (such as microwaves from an antenna, shown here) the term "radiation" applies only to the parts of the electromagnetic field that radiate into infinite space and decrease in intensity by an inverse-square law of power so that the total radiation energy that crosses through an imaginary spherical surface is the same, no matter how far away from the antenna the spherical surface is drawn. Electromagnetic radiation includes the far field part of the electromagnetic field around a transmitter. A part of the "near-field" close to the transmitter, is part of the changing electromagnetic field, but does not count as electromagnetic radiation.

electromagnetic radiation, such as radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, and gamma radiation (γ)

Herschel, like Ritter, used a prism to refract light from the Sun and detected the infrared (beyond the red part of the spectrum), through an increase in the temperature recorded by a thermometer.

A 22° halo around the Moon in Atherton, California

Optical phenomena

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A 22° halo around the Moon in Atherton, California
A solar halo as seen from 41° south latitude
A circumzenithal arc over Grand Forks, North Dakota
The Belt of Venus over Paranal Observatory atop Cerro Paranal in the Atacama Desert, northern Chile
Green flash appears above the solar disc for a second or so. One such occurrence was taken from Cerro Paranal.

Optical phenomena are any observable events that result from the interaction of light and matter.

One famous observation is of the bending of light from a star by the Sun observed during a solar eclipse.