Chromosphere

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Image of the sun during the total solar eclipse on August 11, 1999 , with chromosphere (red) and corona

The chromosphere ( Greek. Color envelope ) is the photosphere subsequent gas layer in the atmosphere of the sun . It consists predominantly of hydrogen and helium , extends up to about 2,000 kilometers over the photosphere and then merges into the solar corona .

properties

Without optical aids such as special filters , the chromosphere can only be observed for seconds during a total solar eclipse . It then appears at the edge of the sun as a deep reddish, upwardly jagged structure. Otherwise it is completely out of the photosphere outshines .

The gas density of the chromosphere decreases with height from 10 −11 to 10 −15  g / cm³. At the same time, the temperature drops from 5800  K on the photosphere to below 4000 K, until it then rises again to around 10,000 K in the upper chromosphere. Within a few thousand kilometers, the chromosphere passes into a transition layer and from there into the corona, which is heated to 1 to 2 million degrees due to effects that have so far been poorly understood.

Because of its low density, the chromosphere only makes a negligible contribution to the total radiation of the sun .

Spicules

During the solar eclipse in 1877, some scientists noticed countless upwardly directed gas splashes in this narrow, briefly visible color fringe. They were called spicules after their shape (lat. Spicula = points, skewers ), but their nature remained a mystery for a long time. It was very vividly interpreted by its first discoverer, Angelo Secchi SJ from the Vatican Observatory. He likened the spicules of the chromosphere to the flames of huge bushfires or a burning prairie . The chromosphere grows " out of an even sub-layer [note: the photosphere] and gives the impression of flames constantly beating up ".

As was only recognized around 1950, the "flames" are extremely fast, tubular flow channels along magnetic fields . They are caused by strong convection vortices under the photosphere, which transport the radiant heat from the inside of the sun to the outside. The spikules that shoot up everywhere have a diameter of up to 1,000 km and can reach 10,000 km in a few minutes, but then collapse again.

Notice of shock waves

Although the force play of the coils is still unclear in detail, it is probably related to strong magnetic fields and violent shock waves . Their entirety contributes to the heating of the chromosphere and the lower corona layers. As in the corona above, the temperature of the gas splash is 1–2 million Kelvin.

In 1957, the sun researcher Otto Kiepenheuer imagined the whole (relatively thin) chromosphere as the spray of the billowing photosphere ocean with its eternally rising granulation eddies. Just as the light splashes of the ocean surf develop much higher speeds than the heavy waves of the sea , the spikule splashes are also much faster than the flow processes in the much denser photosphere. This picture essentially corresponds to the processes on shock fronts that can be easily calculated today .

literature

Individual evidence

  1. ^ Karl Otto Kiepenheuer: Die Sonne , p.56f, Springer-Verlag, Berlin-Heidelberg 1957
  2. Spikulen: Rays on the Sun , accessed November 20, 2013
  3. “The Sun as the Central Point” , accessed on November 20, 2013

Web links