The Sun

The Sun in our galaxy is a star -like yellow dwarf among others: the Milky Way contains between 200 and 400 billion stars, whose 20-40000000000 would be yellow dwarf . Like any star under the laws of the physical current, allows the mass density in his heart to be high enough to cause reactions of thermonuclear fusion continuously. Every second the sun's core fuses 564 million tons of hydrogen and produces 560 million tons of helium . The mass difference between the proceeds (helium) and reactive (hydrogen), or 4 million tons, the equivalent mass of the huge amount of energy produced: 4 × 10^26  watts , which is the energy radiated into space in the form of electromagnetic waves such as visible light.
The Sun is a yellow dwarf moderately large, but the name is misleading since the Sun is larger and brighter than most stars of the Milky Way (most of the stars of the Milky Way is the red dwarf , smaller). It is located in the middle of the main sequence of the Hertzsprung-Russell  , however, the stars brighter and hotter than the Sun are rare, while stars less luminous and cooler are common.

The Hertzsprung-Russell the main sequence is from bottom right to top left.
It is believed that the Sun's position on the main sequence indicates that it is far from having exhausted its supply of hydrogen for nuclear fusion. To date, calculations establish that it has dispersed in the form of energy 3 thousandths of its initial mass. It becomes progressively brighter: early in its history, its luminosity was less than a third of that of today.
Calculating the ratio of hydrogen and helium in the solar interior suggests it is about midway of its life cycle. In more than five billion years, he leaves the main sequence and become bigger, brighter, cooler and red: a red giant ,. At that time, its brightness will be several thousand times that of today.
The Sun is a Population I star  , was born after one or several "generations" of stars. It contains more elements heavier than hydrogen and helium (the "metals" in astronomical language) that the population II stars. These metallic elements were formed in the explosion of nuclei more massive stars, the supernovae . The oldest stars contain few metals, while stars later contain and more. It is believed that this high metallicity was essential for the development of the planetary system, because planets form by accretion of "metals"