What is a solar photosphere


Photosphere, the innermost layer of the sun or other stars that is still accessible to direct observation. It is from here that most of the solar radiation emitted into space in the visible spectral range comes from. Within its layer thickness of only about 350 km (this corresponds to about 0.02% of the sun's diameter), the intensity of the visible radiation drops to almost zero, which makes the solar disk appear sharply delimited. The temperature of the photosphere decreases, starting with about 7,000 K, towards the outside and reaches a minimum of 4,800 K at the border to the chromosphere. This leads to a variation of the surface brightness from the center of the sun disk to the edge (center-edge variation). The gas density also decreases within the photosphere (from about 3 x 10-7 g / cm by a power of ten).

The photosphere spectrum is identical to the solar spectrum observed from Earth. It is the continuous spectrum of a black body with a radiation temperature of 5 780 K. It is superimposed on absorption lines, some of which, however, only arise when sunlight passes through the earth's atmosphere. The so-called Fraunhofer lines became known very early on. About 73% of the solar absorption lines have been identified to date and prove the presence of at least 67 different elements in the sun.

In the visible spectral range, the solar disk shows a grainy structure (granulation). Much more noticeable are disturbances in the solar photosphere, which include sunspots and photosphere flares. Local radial movements in the photosphere also cause the sun to oscillate and allow conclusions to be drawn about the structure of the sun's interior.