Recombination lights

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Luminous phenomena of gas atoms and molecules are referred to as recombination lights , which after ionization by strong radiation sources release their additional energy in the form of photons . This radiant recombination is an important reaction for astronomy and plasma physics and consists in the union of electrically positive and negative charge carriers to form electrically neutral particles. It represents the reverse process to ionization.

Earth atmosphere

In the earth's atmosphere , the air molecules - especially oxygen, nitrogen and sodium - are ionized during the day mainly by the UV component in sunlight . After sunset, their recombination glow causes a slight, natural brightening of the night sky . In addition, however, there is also the scattering of starlight and terrestrial light sources, which mainly occurs in the lower kilometers of the atmosphere (the troposphere ), as well as on floating dust particles ( aerosols ).

Recombination is also responsible for the lighting up of shooting stars and fireballs in the high atmosphere. The smaller of these bodies, coming from interplanetary space, evaporate already at a height of about 100 km through friction with the air molecules, ionizing them. The traces of light do not come from the glow itself, but shortly afterwards from the union of electrons and ions .

astronomy

In astrophysics , the recombination glow is particularly important in gas nebulae when they are excited by hot stars in their vicinity. In areas of star formation , the young stars , which radiate strongly in UV light, usually form inside such molecular clouds , which means that the luminous phenomena are particularly strong. In the particularly bright emission nebulae such as the Lagoon Nebula (M8) in Sagittarius or the Orion Nebula (M42), it is primarily the recombination of ionized hydrogen and helium . Sometimes it takes place in real cascades between the electron shells n → n − 1 → n − 2 etc., i.e. in the case of hydrogen in several violet to red spectral lines of the Balmer series . Recombination glow is also predominant in H-II regions - the expanding successor stage of star formation - and in planetary nebulae around former giant stars.

literature

  • Arnold Hanslmeier : Introduction to Astronomy and Astrophysics. 3. Edition. Springer-Spektrum-Verlag, Berlin / Heidelberg 2014.
  • S. & P. ​​Friedrich: Handbook Astronomy. Oculum-Verlag, Erlangen 2015.
  • Walter Baier et al .: Electronics Lexicon. Franck publishing house, Stuttgart 1974.