
Properties and gereral information about the sun
The average distance between earth and Sun is 150 million kilometers. Nevertheless the Sun is our
nearest star and so the most important celestial body for us. The Sun consists of plasma an ionized gas. That
means the atoms which consist of negative electrons, positive protons and neutrale neutrons do not have the same
amount of protons and electrons any more so they are charged.
The picture shows the comparison of dimensions.


The Suns mass is about 1.98 x 10^{30} kg which is more than 99% of the whole mass of the solar system.
Its radius is 6.96 x 10^{8} m, about 109 radii of the earth.
The shape of the Sun is not very different to a sphere. Thats why you can calculate easily its density
of 1400 kg/m^{3}. In comparision the density of the earth is about 5515 kg/m^{3}. In fact density
increases from outside to inside and has in the center a value between 1.4 and 1.8 x 10^{5} kg/m^{3}.
Because of the huge mass of the Sun its gravitational acceleration has a value of 274 m/s^{2}, 28 times
higher than the gravitational acceleration of the earth.
Like the earth which rotates in 24 hours also the Sun rotates in 27 days. But the suns rotation is differentional that means
it rotates at the equator faster (24 days) than at the pol regions (31 days).

Because of the amount of different definitions of temperature it is not possible to give an
exact value of temperature. The most current definition is the effective temperature.
That is the temperature a black body has which emits the same amount of radiation. A black body
absorb the whole received radiation gets a higher temperature and emit again. Irradiation and
Emission are equal. The value of the effective temperature of the Sun is 5777 K. The temperature of the visible
surface has a value of 4100 K but the temperature of the corona increases of 20 million K. In the core of the Sun
the temperature reaches a value of 15 million K, which is necessary for core fusion. By core fusion energy is produced.
The luminosity is the amount of radiation the Sun emits per second and has a value of
3.86 x 10^{26}W.
The fraction of luminosity which reaches the earth is called solar constant and has a value of 1367 W/m^{2}
with slightly variations.

