All muscle tension depends on sunlight

solar radiation or Solar radiation is the radiation emitted by the sun. The electromagnetic spectrum of the sun has the greatest intensity in the range of visible light (sunlight). Depending on the wavelength, solar radiation is absorbed by the atmosphere to a greater or lesser extent. The intensity that hits the earth's surface also depends heavily on the weather and the position of the sun.

The mass particle radiation emitted by the sun in addition to the electromagnetic radiation is usually not counted as part of the solar radiation. It consists of the charged particles of the solar wind and the neutrinos, which are created in the interior of the sun during nuclear fusion.

Solar spectrum

The electromagnetic radiation of the sun has its maximum at about 500 nm wavelength (blue-green light), but ranges from hard X-rays with less than 0.1 nm to long radio waves. The spectrum is from about 140 nm (UVC) to about 10 cm (microwave) approximately that of a blackbody at a temperature of almost 6000 K, the temperature of the photosphere.

In the range from near infrared radiation (NIR) to the UV, the spectrum contains a large number of absorption lines, the so-called Fraunhofer lines. They arise from the absorption of radiation in the photosphere of the sun.

Solar flares, the frequency of which depends on solar activity, briefly increase the radiation in the X-ray range by several orders of magnitude, but make little contribution to the total radiation. Often they are accompanied by long-wave radio radiation (radio bursts), which depending on the intensity profile as Type I. to Type V is categorized.

Radio emission

The calm sun shines in the entire radio window. There, their spectrum is no longer that of a black body, rather the effective temperature increases from approx. 6000 K at 1 cm wavelength to 1,000,000 K at 10 m. The apparent diameter of the sun also increases with the wavelength, and the radiation is increasingly dominated by the outer atmosphere. The calm sun is thermal bremsstrahlung of free electrons. The most important radiation components of a disturbed sun are:

  • Slow change in radiation proportional to the number of sunspots, plus solar radio flux index.
  • Noise storms above 100 MHz, lasting several days.
  • Radiation bursts often in connection with flares and CME, lasting seconds to days. They are divided into categories I. to V. in meter and decimeter waves and microwave bursts in centimeter waves, synchrotron radiation, supra-thermal electrons that spiral around magnetic field lines.

Solar constant

The total electromagnetic radiation output of the sun is dominated by the thermal radiation of the photosphere, which fluctuates by less than 0.1%. The power falling to earth fluctuates by almost 7% over the course of the year due to the eccentricity of the earth's orbit. The average power per area is called the solar constant. It is considered outside the earth's atmosphere and amounts to


The neutrinos produced in the interior of the sun during nuclear fusion carry away 2% of the fusion power.

Attenuation by the atmosphere

The intensity of solar radiation is lower on the ground than outside the atmosphere, the absorption and scattering of which is strongly dependent on the wavelength: the portion that can be perceived by the human eye, which makes up almost half of the solar radiation, mostly reaches the surface of the earth in clear weather and high sunshine. The invisible radiation is predominantly near infrared radiation (NIR), about a quarter of which is absorbed in the atmosphere, mainly by water molecules. Of the ultraviolet radiation, which makes up less than 10% of the radiation, UVA penetrates to a large extent, mainly weakened by Rayleigh scattering, which is also responsible for the fact that the sky is blue and one turns brown in the penumbra. UVB is strongly absorbed by the ozone layer, UVC by atmospheric oxygen.

The exact calculation of the radiation flux depending on the position of the sun and height above sea level is difficult. As an approximation, one only takes into account the layer thickness of the atmosphere to be penetrated in Air mass-Units (air mass) and the duration of sunshine. Clouds reduce direct radiation, while haze increases diffuse radiation. Diffuse radiation and direct radiation in one place together result in global radiation.


If the solar radiation falls at an angle, it is distributed over a larger surface of the earth and the irradiance drops. This effect runs with the sine of the elevation angle. The influence of the seasons in the tropics is hardly noticeable. Since the position of the sun is always steep there at noon, there is a daytime climate. Outside the tropics, there is an increasing difference between summer and winter towards the poles, both due to the angle of incidence and the increasing differences in the length of the day towards the poles.

In Central Europe, the midday summer sun is 60 ° to 65 ° high and, in ideal weather conditions, radiates with an irradiance of around 700 watts / square meter. In winter it is only 13 ° to 18 ° and even at noon it is only about 247 watts / square meter.

The warming of the earth's surface depends on the length of the bright day. At the end of June the duration in Central Europe is around 16 hours, in December eight hours. The ratio of the total irradiated solar energy is about 5: 1 to 10: 1 between these months, but is mitigated by heat storage mainly by the seas (Maritime climate).

In the microclimate, the irradiance depends on the angle of irradiation as well as on the sun exposure.


The measurement of solar radiation is carried out using a pyranometer, pyrheliometer or sunshine autograph. The latter are mainly used to determine the duration of sunshine. The solar constant, on the other hand, is measured using radiometers.

Radiation balance

The temperature of the earth's surface is globally determined by the radiation balance, the radiation budget. This records the interaction between absorption and reflection as well as re-emission and scattering.

See also

This article uses material from the Wikipedia article "Sunlight", which is released under the Creative Commons Attribution-Share-Alike License 3.0. There is a list of all authors in Wikipedia