The sun quantified

A radius of 700 000 km, a total mass of 2.10 27tons, a temperature close to absolute external 6000 ° K, but internal about 15.10 6 K, as appears to modern astronomers the Sun around which the earth and other planets. We believe that the extraordinary energy supplied by the sun's origin continues the transformation of hydrogen, its main constituent, helium, and its mass is such that it is estimated that this reaction may continue, without weakening, for several billion years. Its luminous surface, or photosphere, to the earth emits visible light (0.4 to 0.7 μ approximately wavelength), and other rays, larger and shorter wavelength, partially arrested by our atmosphere, so that practically the surface of our planet receives most directly the sun rays whose wavelength is between 0.25 to 0.30 μ (the ultraviolet limit) and 2.5 to 3 μ (the infrared limit).
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In addition, another part of sunlight is absorbed by the earth's atmosphere, which heats up and emits inwards, rays of greater wave length (from 3 to about 35 or 40μ) .

Different radiation received by earth from the sun, but their intensity is much lower than those just listed, they are especially noticeable during the eruptions which agitate periodically surface of this planet. First come the airwaves (whose wavelength ranges from 1 cm to 20 meters), their intensity, often negligible, may in case of solar flare, be multiplied by a thousand or even one million . They are also rays of very high energy (gamma and X for example), whose wavelength is a few fractions of a micron, which are manifested by the polar auroras in the upper atmosphere, or, after multiple shocks with molecules of air (rich in ozone at high altitudes), reach the ground level considerably weakened. Measurements with artificial satellites have in recent years to significantly advance our knowledge in this field.

The total energy received from the sun in one day, the earth (radius R), assuming as solar constant (number of calories per gram per square centimeter per minute, intercepted by the average cross section of our globe) The figure of 1.94 is provided by the following equation:

Of the total of 700 ly, 300 ly of (about 43%) comes directly from the sun and sky (as rays of relatively short wavelength - 0.25 to 3μ, as stated above) and the remainder comes from. the atmosphere as infrared radiation of greater wavelength.

However, we admit, since PLANCK, EINSTEIN, DE BROGLIE (to name physicists who have made the newest views on this matter), that radiation is formed by an infinity of particles of energy called photons, associated to electromagnetic waves. This concept is, however, difficult to assimilate completely, but it is necessary to admit, if we want to capture all the effects of radiation. EINSTEIN himself defines these photons, such as small grains, "peas" of light, moving at great speed, which can not be exceeded (300 000 km per second in a vacuum). Each photon carries a "quantum energy"

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variable with the wavelength associated with it, and when it is connected by a simple expression:


For example, and an approximate way, the energy of a photon purple at the end of the visible spectrum, is 3.12 eV, one photon of red at the other end of that spectrum, 1 , 77 eV.

In this sense we can say that the energy of solar radiation is quantified. Our 300 ly / day, amounting to an average energy received at the earth's surface, are physically represented in this theory, by an extremely large number of photons. By analogy with the number N (6.10 23), well known to chemists, which represents the actual number of molecules contained in a molecule - gram of matter, physicists use a special unit: the "Einstein" which corresponds to the sum energy provided by N (6.10 23) photons, which, according to the wavelength associated with them, is also expressed in calories per gram, watts, or joules.

Here's still a small table summarizes the main characteristics of some visible light:


Solar radiation includes, as we know, radiation wavelength and different energy, this results in both theoretical considerations and experimental data. As a rather crude, we can estimate that an average day, each square centimeter of horizontal surface of our planet receives from the sun and sky, from 3 to 4.10 21 photons. This assessment is, of course, made with a very broad approximation