Maybe many of you already know that Earth is a planet and the Sun is the star in our solar system. But what are the major difference between stars and planets?

A star is a basically a huge mass of gas held togethers gravity. It emits light and the light is powered by teh nuclear fusion inside its core. This nuclear fusion is technically a reaction turning hydrogen nuclei into helium nuclei. And that is what our Sun is doing right now.

We have learned that our Sun is at its middle age, which means it is at the most active stage, which lots of hydrogen turning into helium. Once all the hydrogen has been converted into helium, the Sun (and so does the other stars) will collapse and contract.This is a reaction turning hydrogen into carbon. During this phase, the star will expand in size. Sometimes the collapse and expansion occur almost simultaneously and this process is accompanied by an explosion called a supernova. This expansion makes the star look brighter and finally become a red giant. As the red giant becomes more and more massibe, it will eventually collapse into a white dwarf. The prevailling  theory of stellar evolution states that white dwarf stars will eventually turn into black dwarfs.If mass continues to build up, then the star will collapse into neutron stars or even black holes that sucks everything in. 

Different from stars, planets shines by reflected light from the stars. For example, we see the Mars in our telescope only because the sun light is refelcted on the surface of Mars. Since the defintion of planet changes all through the years, we don't really have a clear defintion. However, it is obvious that planets change location in the sky while  stars don't.