The SunThe Sun is a giant thermonuclear furnace with an
internal temperature estimated to be 15 million degrees Celsius.
Hydrogen nuclei collide at such an extremely high speed they fuse to
form helium nuclei generating enormous amounts of heat in the
Figure 2.3 Structure of the Sun
Sunspots are dark, cooler regions of strong magnetic fields on the photosphere whose activity varies through an eleven year cycle. Solar flares occur in the region of Sun spots, sending energized, charged particles at great speeds toward Earth. They form when the Sun's magnetic energy becomes unstable Figure 2.4 Glowing arcs of gas surrounding sunspots. Courtesy NASA. A solar prominence is an arch of gas held above the Sun's surface by strong magnetic fields and lasting up to several months. Their eruptions release massive amounts of large amounts of solar material.
Video: Striking a Solar Balance |
core. The
heat works its way to the luminous outer surface called the photosphere.
Here temperatures fall to about 6000oC
generating a maximum wavelength of emission in the visible end of the
electromagnetic spectrum. Above the photosphere lies the chromosphere and the corona. The chromosphere acts as
a boundary between the cooler photosphere and hotter outermost layer
the corona. 
and collapses causing an explosive heating of gases.