Introduction
The sun is a large fire ball with a radius of 700,000 km (700 Mm) and mass of
2 x 1030kg .
As the energy source of the whole solar system, the it is constantly radiating
light and heat in terms of electromagnetic waves. It has luminosity or power of
4 x 10 26 Watts, with a surface temperature of 5780K.
It is not a planet but a star in the red
dwarf phase.
Structure of the Sun
Generally, the sun can be conveniently divided into 8 regions as with
properties as shown below:
| Region | Inner Radius(Mm) | Temp(K) | Density(g/cm 3) | Properties |
|---|---|---|---|---|
| Core | 0 | 15M | 150 | Energy generated by fusion |
| Radiation zone | 200 | 7M | 15 | Radiative transport |
| Convection zone | 500 | 2M | 0.15 | Convective transport |
| Photosphere (Visible Edge) |
696 | 5.8K | 2X10-7 | EM radiation escape freely |
| Chromosphere (Inner Atmosphere) |
696.5 | 4.5k | 5X10-9 | Cool lower atmosphere |
| Transition zone | 698 | 8k | 2X10-13 | Rapid temperature rise |
| Corona (Outer Atmosphere) |
706.5 | 1M | 10X10-15 | Hot,lower density upper atmosphere |
| ||||
| Solar wind | 10,000 | 2M | 10X10-26M | Solar material |
The first 4 regions constitute the body of the sun and the other 4 regions can be regarded as forming the solar atmosphere.
Core
The core is the innermost region of the sun that is bounded by a sphere of
radius 2/7Rsun. Hydrogen is being cooked at a
temperature higher than imaginable by man, for at least 4.6 billion years in
the process of nuclear
fusion.
Radiative Zone
In the radiative zone, which is the region between the core and a spherical
shell of radius 5/7Rsun, the available energy from
the core is radiatively transported outwards. The material here does not
move.
Convective Zone
The convective zone occupies the region beyond the radiative zone up to
almost the edge of the sun. Energy is transported outwards by convection.
Hot solar gas, which has been heated by energy passing through the radiative
zone, expands and moves outwards; it cools, and falls inwards. Thus matter
moves in cells, and energy is being transported out to the solar edge.
There are many layers of convective cells with their size decreasing towards
the surface. They are responsible for the granulated
appearance of the solar surface.
The Photosphere
The photosphere, which is the thin region lying above the convective zone
right to the solar visible edge, is the "surface" of the sun. It
is also known as the solar disk. In this
region, the gas is not convecting, but energy is transported by radiation.
The disk has quite a sharp edge or limb,
since most of the photons in the visible range originate in this thin
photosphere, which has a thickness of about 500 km.
The Solar Eclipse
<< Click to see picture of a Solar Eclipse
People have traveled the world over just to see such beautiful fleeting events some of which may last only a minute. Often clouds come in at just the critical period.
In this case, as one may guess or gather from the above illustration, an eclipse of the sun occurs when an observer on some part of the Earth enters the shadow cast by the moon.