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The Sun may be said to illuminate, which is a measure of the light within a specific sensitivity range. Many animals (including humans) have a sensitivity range of approximately 400–700 nm, [ 43 ] and given optimal conditions the absorption and scattering by Earth's atmosphere produces illumination that approximates an equal-energy illuminant ...
A UV index reading of 11 or more means extreme risk of harm from unprotected sun exposure. Take all precautions because unprotected skin and eyes can burn in minutes. Try to avoid sun exposure between 10 a.m. and 4 p.m. If outdoors, seek shade and wear sun-protective clothing, a wide-brimmed hat, and UV-blocking sunglasses.
The Sun is classed as a G2 star, [66] meaning it is a G-type main-sequence star, with 2 indicating its surface temperature is in the second range of the G class. The solar constant is the amount of power that the Sun deposits per unit area that is directly exposed to sunlight.
The Sun closely approximates a black-body radiator. The effective temperature, defined by the total radiative power per square unit, is 5772 K. [12] The color temperature of sunlight above the atmosphere is about 5900 K. [13] The Sun may appear red, orange, yellow, or white from Earth, depending on its position in the sky.
Solar radius is a unit of distance used to express the size of stars in astronomy relative to the Sun. The solar radius is usually defined as the radius to the layer in the Sun 's photosphere where the optical depth equals 2/3: [ 1] 695,700 kilometres (432,300 miles) is approximately 10 times the average radius of Jupiter, 109 times the radius ...
Solar flares are eruptions of electromagnetic radiation originating in the Sun's atmosphere. [1] They affect all layers of the solar atmosphere (photosphere, chromosphere, and corona). [2] The plasma medium is heated to >10 7 kelvin, while electrons, protons, and heavier ions are accelerated to near the speed of light.
Evolution of the solar luminosity, radius and effective temperature compared to the present-day Sun. After Ribas (2010) The solar luminosity (L ☉) is a unit of radiant flux (power emitted in the form of photons) conventionally used by astronomers to measure the luminosity of stars, galaxies and other celestial objects in terms of the output of the Sun.
The Sun's corona is much hotter (by a factor from 150 to 450) than the visible surface of the Sun: the corona's temperature is 1 to 3 million kelvin compared to the photosphere's average temperature – around 5 800 kelvin. The corona is far less dense than the photosphere, and produces about one-millionth as much visible light.