SOLAR
SYSTEM
STARS
BLACK
HOLES
METEORS AND
METEORITES
ASTEROIDS
COMETS
GALAXIES
NEBULAE
GLOSSARY
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![](images/Sun/Sol2.jpg) |
The sun: Nearest
of Stars
The sun lies in the Orion arm of the Galaxy,
which is marked by the dark and bright nebulae from which new stars
are constantly born. More than twenty star subsystems lie within
13 light-years of the Sun.Only four of these are visible to the
naked eye.The nearest subsystem, Alpha Centuari is triple. Several
others are binary stars.
The Sun is the most dominant member of the Solar System because
of its gigantic mass.Its diameter is 1,392,000 kilometers more than
109 times the equatorial diameter of the Earth and its volume is
1,303,600 times that of our planet Earth. The distance between the
Earth and the sun is called 'One Astronomical Unit' and is used
to measure the distances in the Solar System.
When the Sun was studied through telescopes, using special filters,
it was found that it is not a solid body as it seems to the naked
eye, but it is completely gaseous. The surface layer of the Sun
as we see it is the 'Photosphere'. This photosphere is about 500
km thick, and we do not see anything inside.It is from this region
that the Solar radiation escapes. To the eye it appears smooth but
under telescope magnification its mottled structure can be seen.
The mottled structure of the Photosphere or Granulation is caused
by columns of hotter gases rising from below the Photosphere.The
darker intergranular regions are caused by the cooler gases sinking
back.Individual granules have a life of several minutes only.
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Solar Atmosphere:
Overlying the Photosphere there is a thick
layer known as the Chromosphere.It has a thickness of about 10,000
km. The outermost zone that lies above the Chromosphere is known
as the Corona. In some parts of the Corona, temperatures may rise
as high as 1,000,000 degree K.However, its density is very low.
During total Solar Eclipse the Corona becomes visible to the naked
eye as a beautiful pearly halo surrounding the Sun. The Corona is
referred to as the Sun's atmosphere. Deep inside the Sun at its
innermost region, the temperature is about 14,000,000 degree K.This
is the Core of the Sun.The energy liberated from the Core is transported
to the Photosphere through the two zones called the Inner Radiative
Zone and the Outer Convective Zone.The diameter of the Sun as defined
by the Photosphere is about 1,392,000 km.The volume of the Sun is
about 1,300,000 times that of the Earth.Its mass is about 750 times
the combined mass ot the all the other bodies in the Solar System.Deep
in its interior, the density of the sun increases and the hot gases
under severe compression become 10 to 20 times denser than iron
Earth.
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![](images/Sun/sun06.gif)
Sun
Spots
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