We can look out into the night sky and see billions of stars shining brightly. The number and brightness will depend on where you live. People that live in cities have a lot of bright lights that keep them from seeing as many stars, but those that look up at the sky in the country can see many more. Stars are actually suns, in the same way that our sun is a star. If you went out into the far reaches of the galaxy and looked back on our sun, it would look like a star.
To figure out why the stars shine, you have to know what they are made of. Stars are balls of glowing plasma, so hot that we can’t even imagine the temperatures. The surface of a star like our sun is cooler at the surface (5,800 Kelvin) but its core is the hottest place, at 15 million Kelvin.
They are held together through their own gravity and they give off some of the heat that they produce. Stars come in all sizes. Some are incredibly large, and oddly, it is the larger ones that have the shorter lifespan. Others are very small and they exist for longer periods of time. Our sun is a medium-sized star and still has millions of years to exist.
The process of producing the heat for each star involves fusion. The energy is trapped inside the sun for millions of years, constantly trying to get out. Finally, after it rises into the outer areas of the sun, the energy escapes and it is carried off as solar wind.
The next thing that you need to think about as a reason the stars shine is the speed of light. Light travels at a specific speed and will continue to travel until it hits something that blocks it. When we look into the night sky we are seeing the light from billions of stars that are at many distances from the earth.
Depending upon the distance, some of the light that is shining could have come from stars that gave off that light millions of years ago. We are actually seeing the moment that each sun released the energy that had waited and fought to get outside of the sun and was carried through the universe to us.
Each time we see the light of a star, we are seeing a star’s past. If we had the chance to actually travel to where that star is located, we would notice that many things have changed from the moment it released the energy until the time it traveled to reach our site. In some cases, a star could have lived and died; becoming a white dwarf or even exploding and going ‘nova’. If we were actually there and looked back, we might also see the light from our own sun, but that would be light that was sent out millions of years before.
So the answer to the question as to why stars shine is really that they are a powerhouse of energy, with gigantic cores of fusion reaction that causes energy to be released and sent out into the universe as light.