In addition to the cosmic rays (particles animated of one speed and of an energy extremely high), the Sun rayon of the electromagnetic waves whose spectrum extends from the decametric waves with the gamma rays while passing by the visible Light.

The intensity of the radiation is not constant and increases enormously at the time of the solar eruptions during the maximum ones of the solar Cycle. One distinguishes three categories of solar radiation:

• the emission of the calm Sun (see Constant solar),
• the component slowly variable,
• the solar starts.

The waves radio emitted by the Sun come mainly from the plasma S constituting the Chromosphère and the crown. The centimetric waves correspond to the low layers of the chromosphere tandis that the crown emits decametric waves. Plasma acts in fact like a high-pass Filtre of which the Fréquence on cut depends on the electronic density of the medium. This frequency (in Hz) is calculated with the following formula:

$f\; =\; 9\; \backslash \; sqrt\; \{N\_e\}$

where N_e is the electronic density of plasma in electron s/m³. For example, in the chromosphere, to 18.000 K, the electronic density is equal to 10¹⁸ and the frequency of 9 GHz (Wavelength 3 cm).

A weak part of the solar radiation arrives to the surface of the Ground, of the decametric radio waves with the softest rays Ultraviolet S, the remainder being reflected or being filtered by the atmosphere and the Ionosphere. The study of the electromagnetic radiation of the Sun by the Radioastronomie allowed enormous progress in the comprehension of the inner working of the Sun.

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