The Sun, like other stars, was formed in a nebula, an interstellar cloud of dust and gas (mostly hydrogen). These stellar nurseries are abundant in the arms of spiral galaxies (like our galaxy, the Milky Way).In the stellar nursery, dense parts of the clouds undergo gravitational collapse and compress to form a rotating gas globule.

The globule is cooled by emitting radio waves and infrared radiation. It is compressed by gravitational forces and also by shock waves of pressure from supernova or the hot gas released from nearby bright stars. These forces cause the roughly-spherical globule to collapse and rotate. The process of collapse takes from between 10,000 to 1,000,000 years.
A Central Core and a Protoplanetary Disk:
As the collapse proceeds, the temperature and pressure within the globule increases, as the atoms are in closer proximity. Also, the globule rotates faster and faster. This spinning action causes an increase in centrifugal forces (a radial force on spinning objects) that causes the globule to have a central core and a surrounding flattened disk of dust (called a protoplanetary disk or accretion disk). The central core becomes the star; the protoplanetary disk may eventually coalesce into orbiting planets, asteroids, etc.
The contracting cloud heats up due to friction and forms a glowing protostar; this stage lasts for roughly 50 million years. If there is enough material in the protostar, the gravitational collapse and the heating continue.

More than 5 billion years ago, there was no Sun, no Earth, no solar system at all. There was, instead, just a huge, thin cloud of gas and dust slowly turning and drifting through space.

Orion Nebula – Formation of a Solar System Example

Gradually, the cloud became smaller. Because of its own gravity it pulled itself together. At the same time, it began to get hotter and denser.

In its old age, the Sun may shed a colorful nebula like this one

By about 5 billion years ago, nearly all the cloud’s gas was packed into a big, fuzzy ball at the center of the cloud. Then a very important thing happened. Deep inside the ball, the temperature rose high enough for fusion to start. Hydrogen began to turn into helium, making light and heat. What had been a ball of gas became a star: the Sun.

A Newborn Star:
When a temperature of about 27,000,000°F is reached, nuclear fusion begins at the core of the Sun. This is the nuclear reaction in which hydrogen atoms are converted to helium atoms plus energy. This energy (radiation) production prevents further contraction of the Sun. Young stars often emit jets of intense radiation that heat the surrounding matter to the point at which it glows brightly. These narrowly-focused jets can be trillions of miles long and can travel at 500,000 miles per hour. These jets may be focused by the star’s magnetic field. Later, the Sun stabilizes and becomes a yellow dwarf, a main sequence star which will remain in this state for about 10 billion years. After that, the hydrogen fuel is depleted and the Sun begins to die.

New Young stars
What will happen to the Sun in the future? For billions of years, it will carry on “burning” hydrogen fuel in its core. Although the Sun uses up around 5 million tons of hydrogen every second, it still has enough left its core to last for another 5 billion years or so.

The Sun is about 4.5 billion years old. it has used up about half of its nuclear fuel (hydrogen). In about 5 billion years from now, the sun will begin to die. As the Sun grows old, it will expand. As the core runs out of hydrogen and then helium, the core will contact and the outer layers will expand, cool, and become less bright. It will become a red giant star.

After this phase, the outer layers of the Sun will continue to expand. As this happens, the core will contract; the helium atoms in the core will fuse together, forming carbon atoms and releasing energy. The core will then be stable since the carbon atoms are not further compressible. Then the outer layers of the Sun drift off into space, forming a planetary nebula (a planetary nebula has nothing to do with planets), exposing the core. Most of its mass will go to the nebula. The remaining Sun will cool and shrink; it will eventually be only a few thousand miles in diameter! The star is now a white dwarf, a stable star with no nuclear fuel. It radiates its left-over heat for billions of years. When its heat is all dispersed, it will be a cold, dark black dwarf – essentially a dead star (perhaps replete with diamonds, highly compressed carbon).

When it finally does run out of fuel, though, something very odd will happen to the Sun. It will swell up to many times its present size and become what is known as a red giant.

When the Sun has exhausted its supply of hydrogen to fuse it will swell into the Red Giant phase. The size of the current Sun giant phase.

The outer layers of the Sun will grow to swallow up, in turn, the planets Mercury and Venus. They may even reach out as far as Earth. Then, the surface of our planet will be scorched, and its oceans boiled dry.

As a red giant, the Sun might be able to exist for a few more million years. During this time it will shed matter quite quickly. The solar wind will strengthen to a solar gale. Finally, the Sun may cast off most of its outer layers as a bright shell of gas called a planetary nebula.

All that will be left behind is a very hot, dense core. The Sun, in fact, will have become a white dwarf – a star no bigger than the Earth. Gradually, over many millions of years, even this small star will cool. The Sun will end its days quietly as a dimming ember in space.

Before this happens, human beings may have learned how to travel to other stars. We may be able to make our home on a planet around a friendlier star. But perhaps we will leave behind a robot probe to watch the final fate of our old neighborhood star.

NOW IT IS THE TIME TO TEST UR Astronomy Knowledge:-
1. Is the Sun a star, a planet, or a nebula?_______________________
2. Is the Sun solid, liquid, or gaseous?_______________________
3. During what month is the Sun closest to the Earth? _____________________
4. Where is the Sun hottest? _______________________
5. Where is the Sun coolest?_______________________
6. What element is most plentiful on the Sun?_______________________
7. What element was named after the Sun?_______________________
8. What is the primary atomic reaction that occurs within the Sun that converts hydrogen atoms into helium atoms? 9. How old is the Sun? ______________________
10. Are sunspots hotter or colder than the surrounding areas? _______________________