The Sun shines due to the energy produced in its core through a reaction called nuclear fusion
which requires extreme heat and pressure.
The Sun temperatures reach 16 million degrees Kelvin
and the pressure is so high that nuclear fusion is possible.
In this process energy is released when four hydrogen nuclei
together to form one helium
It takes thousands of years for this energy to reach the surface of the sun and to be emitted into space.
Above the core is the radioactive zone, where the energy from nuclear fusion is transported up by photons
(small energy packets similar to elementary particles such as electrons
The upper layer of the Sun's interior is called a convective zone because this is where convection
in a process similar to convection in the Earth's mantle
Huge hot gaseous bubbles rise and transport the energy up, while the cooler ones travel down.
The visible part of the Sun surface is called the photosphere. Of course, it is not a solid surface;
it is simply the bottom layer of the Sun's atmosphere
. It is still very hot, about 5,840 K.
If you photographed the photosphere it would appear to be covered with rice grains, called granules.
These granules actually are the tops of convective bubbles that carry the energy upwards. Each is about 1,000 km. wide.
Sunspots are formed when the magnetic field
of the sun gets twisted and pokes up through the surface.
The Sun's magnetic field is so strong that it suppresses the energy flow through the spots and lowers the temperature.
This makes sunspots look darker. Sun spots typically form in groups.
Studying the motion of the sunspots shows that the Sun rotates faster around equator, about 29 day, and slower near the poles, about 31 days.
The solar corona
spreads above the photosphere up to 6 solar radii
The temperature rises again and reaches about million degrees.
However, the solar corona is less dense, so it shines with less intensity then the photosphere.
The only way to see solar corona is during the time of a total solar eclipse, when the moon is between the Earth and the Sun.
Since the Moon is about the same visible size as the Sun, during an eclipse the moon covers the sun completely
and blocks the majority of solar light, allowing a magnificent view of the solar corona and solar prominences.
are spectacular feature in the solar corona.
They look like bright loops and arcs because they contain hot gasses that follow the curved lines of Sun's magnetic field.
Solar prominences can loop hundreds of thousands of miles into space.
Astronomers study the Sun with specially constructed telescopes. However, the Earth's atmosphere blocks
the damaging high energy rays from the Sun. If we want to study them we have to use spacecraft.
Early observations were made from the first space station, Skylab
, in 1970.
The main purpose of Ulysses
spacecraft was to study magnetic field of the sun.
The Solar & Heliospheric Observatory (SOHO)
, an international collaboration
between the European Space Association
was launched in 1995 to study the Sun from its deep core to the outer corona and the solar wind.