Stellar atmosphere

As a stellar atmosphere is called the visible outer regions of a star. Physically accurate, it covers light transmissive layers of stars of various kinds

Guided by observations of the Sun, the best-studied star, it is distinguished from the inside out 3-4 hot gas layers:

Photosphere

The photosphere (Greek light cover) is the lowest, densest and coolest layer of the stellar atmosphere. Through it penetrates coming from the solar interior heat radiation than visible light outward.

They dominate the visible star light passes through the upper layer substantially unaffected. The photosphere of the Sun has an effective temperature of about 5800 K. It shows phenomena such as sunspots, bright faculae and granulation, caused by convection -grained structure of the solar surface. The photo Spherical spectrum is determined by properties such as temperature ( essential for the spectral class ), gravitational acceleration (crucial for the luminosity class), and content of heavy elements compared to hydrogen and helium ( metallicity ). Precise physical models of stellar atmospheres and their spectra are therefore an important tool in astrophysics.

Chromosphere

The chromosphere (Greek color cover) is the subsequent upward gas layer. It has its name from the red light that is visible for a short at a total solar eclipse.

It is usually completely outshone by the photosphere. Your temperature rises to a minimum at the upper edge of the photosphere again, its spectrum consists of narrow emission lines, in particular H -alpha at the wavelength of 656.3 nm, which corresponds to a deep red light.

Above the chromosphere is sometimes defined a transition layer to the corona ( in the sun).

Corona (or solar corona )

The corona is visible during solar eclipses " halo ". It consists of a very thin, but hot over one million Kelvin gas. This is heated by different mechanisms and not extending several solar radii in the room. The structure of the " beam " is dependent on the current solar activity. In the sunspot minimum, the corona has a more rounded outline as it appears extended elongated in the equatorial direction in the spot maximum. This is related to the profile of the magnetic field lines that influence the ionized gas strongly.

In the lower part of the solar corona small spicules and prominences are rising far from the chromosphere and of eruptive flares constantly thrown up that often fall again only after several days on the photosphere down.

Atmospheres around other stars

While these atmospheric layers are well researched in the sun, you only the photosphere can explore in more detail in other stars because of their great distance usually. As a rule, only its spectrum is bright enough for that; that of the overlying layers is almost completely outshines.

The existence of chromospheres and coronae Star follows mainly from theoretical models of stellar structure - see there. For some types of stars has however observed similar phenomena, which supports the current theory of stellar structure. So -called star spots have been postulated to near giant stars of brightness variations, the nature of which is likely to correspond to our sun spots.

Some variables show matter eruptions, which are interpreted as corona phenomena or extremely violent solar wind, and Young Stars regularly come from gas clouds that can be compared with the mechanism of spicules.