The photosphere is the radiating layer of the stellar atmosphere in which a continuous spectrum is formed. The photosphere gives the bulk of the star’s radiation.
The photosphere is substantially opaque ( optical thickness ), it absorbs and then re-radiates the energy coming from the bowels of the star. Due to the opacity of the photosphere, energy transfer proceeds in a convective way: in the case of the solar photosphere, convection is observed as granulation of the photosphere , that is, in the form of bright, hot convective cells (granules). The length of the photosphere depends on its transparency and, therefore, density. Thus, the typical length of the photosphere in depth for the Sun is ≈300 km, for white stars of the main sequence of the spectral class A0V - ≈1000 km, for giants of the class G - ≈10 4 –10 5 km, that is, significantly less than the diameter of the star, with which in particular, it is due to the fact that the Sun has a sharp visible edge.
The temperature of the photosphere increases with depth, which causes a visible darkening of the edge of the solar disk: for the same optical path length, the radiation in the center of the disk comes vertically from a greater depth and, accordingly, from the hotter layers of the photosphere, in contrast to the radiation of the periphery of the disk coming tangentially from the colder ones outer layers of the photosphere. On the surface of the sun’s photosphere, large-scale areas of lowered temperature are also observed — sunspots (temperature difference reaches 1500 K ).
A continuous emission spectrum of the star is formed in the photospheres. Above the photosphere, the temperature and transparency of the stellar atmosphere (the chromosphere , in which the absorption lines of stellar spectra and the corona are formed ) begin to rise, reaching millions of degrees in the corona.
Literature
- Photosphere / Khokhlova V. L. // Space Physics: A Little Encyclopedia / Editorial: R. A. Sunyaev (Ch. Ed.) And others. - 2nd ed. - M .: Soviet Encyclopedia , 1986. - S. 706. - 783 p. - 70,000 copies.