The Suns Life Cycle

The sun has billions of years behind and ahead of it. About 4.6 billion years ago it began like other stars, as a cold mass of hydrogen and helium – the solar nebula left over from the big bang. The gas cloud began to shrink under its own gravity and, as it collapsed, the temperature of the core rise from frictional heating as gas molecules collided. When the temperature reached about 10 million ^.C the thermo nuclear reaction began.

The sun has about another five billion years of life ahead of it, as it turns hydrogen into helium in its core. When the hydrogen fuels runs low, it will burn some of the helium nuclei, fusing those into heavier nuclei. But at the same time it will swell into a giant red star, whereupon the Earth will be destroyed. Only a few million years after that, the sun will puff off some of its out layers and then shrink into a white dwarf, with an intensely hot surface, but so small that it gives out little light. It will then cool off for the rest of time.

The Sun Radiation

The Sun puts out its maximum radiation in the yellow part of the optical spectrum but it radiates substantially in the ultra violet and infrared and to a lesser extent at the X-ray and radio wavelengths. These make up the electromagnetic spectrum of transverse waves which all have the same velocity in space.

 The source of this energy is the conversion of mass into energy caused by nuclear fusion reactions that occur within the core. This reaction will only occur at extremely high temperatures and pressures, when gas turns to plasma. In this reaction hydrogen nuclei fuse together to form helium.  Each helium nucleus produced has slightly less mass than the hydrogen nuclei that went into it, and this difference is converted into energy, in accordance with Einstein’s famous principle of the equivalence of mass and energy  E=mc²,where C represents the speed of light and m represents mass. The heat produced by this reaction is sufficient to activate further reactions and so it is self sustaining. Four million tons of matters are converted to energy each second in the Sun and will continue to do so for the next five billion years.