Physically, the universe is composed of matter and energy. We (intelligent and inquisitive humankind) do not yet know how energy and matter came to be. But we now know somethings about them, and some of the consequences of their interactions. In fact, matter and energy seem to be two (probably two of many) different manifestations of the same thing.
Scientists, led by Einstein, say that stars arise by, and because of, this fact of physics: matter-energy interconvertibility.
According to the Einsteinian equation of matter-energy relativity, a tiny quantity of matter can be converted into an enormous quantity of energy; vice versa.
The Sun, the nucleus of our solar system, is a star.
The “dis-materializing” or “decomposition” of matter into energy happens in stars through a process known as nuclear reaction; which is of two known types: Fission and Fusion.
Nuclear fusion is the (main) energy-source of most stars.
Whatever caused the universe arranged the material aspects of it in certain basic units. Three (most known) of the units are called PROTON, NEUTRON and ELECTRON. Any combination of these particles, fundamentally including proton(s) and electron(s) gives an elementary atom.
In the atom as an entity, the nucleus comprise, or is occupied by protons; sometimes neutrons too. These are the nucleons. They are held in union in the centre of the atom by a force-phenomenon called nuclear energy. The electrons spin around the nucleons.
A piece of matter (solid, liquid, gaseous…) composed of same kind of atoms is an element. In otherwords, an atom is the smallest particle of an element: such as helium, carbon, lithium, Hydrogen…
The universe is exceedingly abounding in hydrogen, the simplest of atoms.
‘Eons’ ago, these condensed or gravitated into massive orbs. One of the orbs was what later became the sun, our sun. The pre-star sun (the orb) became a star, and remains so by nuclear fusion.
Nuclear fusion is the union of more than one atom (usually two) into one. The result of this are energies and transmuted materials whose nucleo-chemical nature differ from those of the parent material. Individual atoms of the transmutate may be heavier, but the overall mass of the whole piece of matter becomes less than the input.
Put too simply: atomic nuclei unite, resulting the synthesis of a new kind of atoms and release of great quantities of energy.
About the sun: at a nature-determined volume and internal pressure, the centre of the orb ignited. The whole mass steadily became a furnace of nuclear fusion. Hydrogen atoms fuse(d) and transmute(d) into helium atom, which further transmute into heavier kinds of atoms. Massively incalculable quantities of energies are “spewed” out radially. Heat energy alone so produced raises the temperature of its environment to millions of degrees Celsius.
Parts of the energy reach us as photoenergy which we call sunshine; plus its companion: heat. And other energies too.
Only a tiny part of the sun’s mass is “fused” or “burnt” at a time. It takes many, many years for the eruption caused by a bout of nuclear fusion in the core of the sun to reach the surface. Experts say that if the sun’s nuclear fuel, which is its body mass of hydrogen, is exhausted today, it would take close to 50 million years before the effect could be felt at the surface.
When I say “furnace”, I mean one that is many thousands of time the mass, and millions of time the volume of planet earth; where trillions of trillions of hydrogen atoms fuse simultaneously per second.
The conversion rate from nuclear fuel to nuclear ash in the sun is slow, gradual. There is still an abundance of hydrogen reserve in the sun. So the nuclear furnace is keeping on; and The Sun keeps shining.
