The Sun

(TFS) - The sun is the closest star to earth. It is an enormous gas sphere with a radius 110 times greater than that of the earth, and its mass is about 330,000 times that of Earth, accounting for about 99.86% of the total mass of the Solar System. About three quarters of the Sun's mass consists of hydrogen (73%); the rest is mostly helium (25%), with much smaller quantities of heavier elements, including oxygen, carbon, neon, and iron.  Its heart produces an incredible energy due to the material that burns at a temperature of 15 million degrees! This energy comes to us in the form of warmth and light and allows life on earth. Our planet turns around the Sun, located 150 million kilometers, Its surface is of a blinding brilliance and it is very agitated.
The sun was created 4,5 billion years ago,and it is estimated that in 5 billion years it will burn all of its reserves.

The Sun Profile

diameter: 1,390,000 km.

mass: 1.989e30 kg

temperature: 5800 K (surface) 15,600,000 K (core)

Composition

The Sun is, at present, about 70% hydrogen and 28% helium by mass everything else ("metals") amounts to less than 2%. This changes slowly over time as the Sun converts hydrogen to helium in its core.

Characteristics

The outer layers of the Sun exhibit differential rotation: at the equator the surface rotates once every 25.4 days; near the poles it's as much as 36 days. This odd behavior is due to the fact that the Sun is not a solid body like the Earth. Similar effects are seen in the gas planets. The differential rotation extends considerably down into the interior of the Sun but the core of the Sun rotates as a solid body.

Conditions at the Sun's core (approximately the inner 25% of its radius) are extreme. The temperature is 15.6 million Kelvin and the pressure is 250 billion atmospheres. At the center of the core the Sun's density is more than 150 times that of water.

The Sun's power (about 386 billion billion mega Watts) is produced by nuclear fusion reactions. Each second about 700,000,000 tons of hydrogen are converted to about 695,000,000 tons of helium and 5,000,000 tons (=3.86e33 ergs) of energy in the form of gamma rays. As it travels out toward the surface, the energy is continuously absorbed and re-emitted at lower and lower temperatures so that by the time it reaches the surface, it is primarily visible light. For the last 20% of the way to the surface the energy is carried more by convection than by radiation.

The different phases of the sun:

The « Red Sun »:

In the evening, the solar disk is just above the horizon, and its rays, to reach us, traverse a great thickening of atmosphere. The rays of blue color are deviated towards the sky, only the red rays reach us.

The « fragmented sun »:

On the evening of a very hot day, the solar disk appears on the horizon as elongated cuts. This optical effect comes from the fact that the rays of the sun, crossing the increasingly hot air layers, have been devised.

The «Green Ray »:

 At twilight, just before passing under the horizon, the sun is only a thin line of light. And when the atmosphere is very calm, the last rays that reach us are those of green color.

The Rainbow: 

The light of the sun is composed of seven colors. When it passes through a curtain of rain, each color is deviated differently and emerges separated from the others.

The Polar Aurora :

The solar wind emits a blast charged with electrical particles. When this blast is very strong, the particles reach the Earth, they regroup and concentrate at the poles. There then bursts great sheaves (packs) of light flaunted by flames: which is known as polar auroras.

Eclipses :
The moon revolves around the Earth. At times, it passes just between the earth and the sun. The sun is then hidden by the moon. ; And that is when we have an eclipse of the sun. (Order: sun, moon, earth). 
But the moon, smaller than the sun, does not hide it completely: one can then perceive the edge of the solar disk. (The crown)

It just happens that the Moon and the Sun appear the same size in the sky as viewed from the Earth. And since the Moon orbits the Earth in approximately the same plane as the Earth's orbit around the Sun sometimes the Moon comes directly between the Earth and the Sun. This is called a solar eclipse;

 Total Solar Eclipse

If the alignment is slightly imperfect then the Moon covers only part of the Sun's disk and the event is called a partial eclipse. When it lines up perfectly, the entire solar disk is blocked and it is called a total eclipse of the Sun. 

Total Solar Eclipse

Partial Solar Eclipse

Partial eclipses are visible over a wide area of the Earth but the region from which a total eclipse is visible, called the path of totality, is very narrow, just a few kilometres (though it is usually thousands of kilometres long). Eclipses of the Sun happen once or twice a year. If you stay home, you are likely to see a partial eclipse several times per decade. But since the path of totality is so small it is very unlikely that it will cross you home. So people often travel half way around the world just to see a total solar eclipse. To stand in the shadow of the Moon is an awesome experience. For a few precious minutes it gets dark in the middle of the day. The stars come out. The animals and birds think it's time to sleep. And you can see the solar corona. It is well worth a major journey.

Partial Solar Eclipse

The Sun's satellites

There are eight planets and a large number of smaller objects orbiting the Sun.

Planet	Distance(000 km)	Radius(km)	Mass(kg)	Discoverer	Date
Mercury	57,910	2439	3.30e23
Venus	108,200	6052	4.87e24
Earth	149,600	6378	5.98e24
Mars	227,940	3397	6.42e23
Jupiter	778,330	71492	1.90e27

source: http://nineplanets.org/sol.html