Stellar atmosphere

Stellar Atmosphere

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Stellar atmosphere

The stellar atmosphere is the outer region of the volume of a star

Star

A star is a massive, luminous ball of Plasma that is held together by its own gravity. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth....
, lying above the stellar core, radiation zone

Radiation zone

The radiation zone is the middle zone in the Sun's interior. Energy travels out of the core into the radiation zone. Energy travels through the radiation zone in the form of electromagnetic radiation....
and convection zone

Convection zone

The convection zone of a star is the range of radii in which energy is transported primarily by convection. In the radiation zone, energy is transported by radiation....
. It is divided into several regions of distinct character:

The photosphere

Photosphere

The photosphere of an astronomical object is the region from which externally received light originates. The term itself is derived from Ancient Greek roots, f???- f?t??/photos meaning "light" and sfa????/sphairos meaning "ball," in reference to the fact that it is a ball-shaped surface perceived to emit light....
, which is the lowest and coolest part of the star's atmosphere, is the part which we see.

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Encyclopedia

The stellar atmosphere is the outer region of the volume of a star

Star

Radiation zone

Convection zone

Photosphere

Light

Light, or visible light, is electromagnetic radiation of a wavelength that is Visible spectrum to the human eye , or up to 380?750 nm. In the broader field of physics, light is sometimes used to refer to electromagnetic radiation of all wavelengths, whether visible or not....
escaping from the surface of the star stems from this region and passes through the higher layers. The photosphere of the Sun

Sun

The Sun , a G V star, is the star at the center of the Solar System. The Earth and other matter orbit the Sun, which by itself accounts for about 98.6% of the Solar System's mass....
has a temperature (effective temperature

Effective temperature

The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation....
) of about 5780 K

Kelvin

The kelvin is a Units of measurement of temperature and is one of the seven SI base units. The Kelvin scale is a Thermodynamic temperature scale where absolute zero, the theoretical absence of all thermal energy, is zero ....
. Starspot

Starspot

Starspots are equivalent to sunspot but located on other stars. Spots the size of sunspots are very hard to detect since they are too small to cause fluctuations in brightness....
s, cool regions of disrupted magnetic field

Magnetic field

A magnetism field is a vector field which can exert a magnetic force on moving electric charges and on magnetic dipoles . When placed in a magnetic field, magnetic dipoles tend to align their axes parallel to the magnetic field....
lie on the photosphere.

Above the photosphere lies the chromosphere

Chromosphere

The chromosphere is a thin layer of the Sun's celestial body's atmosphere just above the photosphere, roughly 2,000 kilometers deep. The chromosphere is more visually transparent than the photosphere....
. This part of the atmosphere first cools down and then starts to heat up to about 10 times the temperature of the photosphere.

Above the chromosphere lies the transition region, where the temperature increases rapidly on a distance of only around 100 km. Beyond this region is the outermost part of the stellar atmosphere, the corona

Corona

A corona is a type of Plasma "celestial body's atmosphere" of the Sun or other celestial body, extending millions of kilometres into space, most easily seen during a total solar eclipse, but also observable in a coronagraph....
, a tenuous but extremely hot (million K) plasma

Plasma (physics)

In physics and chemistry, plasma is a partially ionized gas, in which a certain proportion of electrons are free rather than being bound to an atom or molecule....
. While all stars on the main sequence

Main sequence

The main sequence is a continuous and distinctive band of stars that appear on plots of stellar Color index versus brightness. These color-absolute magnitude plots are known as Hertzsprung-Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell....
feature transition regions and coronae, not all evolved stars do so. It seems that only some giants

Giant star

A giant star is a star with substantially larger radius and luminosity than a main sequence star of the same effective temperature. Typically, giant stars have radii between 10 and 100 solar radii and luminosities between 10 and 1,000 times that of the Sun....
, and very few supergiant

Supergiant

Supergiants are among the most massive stars. In the Hertzsprung-Russell diagram they occupy the top region of the diagram. In the spectral classification supergiants are class Ia or Ib ....
s possess coronae. An unresolved problem in stellar astrophysics

Astrophysics

Astrophysics is the branch of astronomy that deals with the physics of the universe, including the physical properties of astronomical objects such as galaxy, stars, planets, exoplanets, and the interstellar medium, as well as their interactions....
is the question as to how exactly the corona can be heated to such high temperatures. The answer lies in magnetic field

Magnetic field

A magnetism field is a vector field which can exert a magnetic force on moving electric charges and on magnetic dipoles . When placed in a magnetic field, magnetic dipoles tend to align their axes parallel to the magnetic field....
s, but the exact mechanism remains unclear.

During a total solar eclipse

Solar eclipse

A solar eclipse occurs when the Moon passes between the Sun and the Earth so that the Sun is wholly or partially obscured. This can only happen during a new moon, when the Sun and Moon are in conjunction as seen from the Earth....
, the photosphere of the Sun is obscured, revealing the other layers of the atmosphere. Under these conditions, the chromosphere appears as a rough reddish ring, and the corona appears as a tufted halo.