What is the difference between a planet and a star?

What is the difference between a planet and a fixed star?

• Answer:

  A star is a ball of (mostly) hydrogen gas, in which the temperature and pressure are so high that nuclear fusion takes place in the core, producing gargantuan quantities of energy. The high temperatures (millions of degrees at the core, "only" tens of thousands of degrees at the surface) cause the star to radiate energy in the form of light, heat, and all the other classifications of electromagnetic energy. A planet is much smaller, and does not produce much energy of its own. It "shines" only by light from the nearby star reflected back into space. Because planets are so small and dim, we are only able to see planets within our own solar system. Using indirect methods, scientists have been able to detect 300 or more "exoplanets", planets in other solar systems; however, only one has actually been visually identified. There is only one star in our solar system; we call it the Sun. The planets, including Earth, orbit around the Sun. Even the nearest stars are incredibly far away; all of the visible planets are, relatively speaking, quite close by. As they looked up into the night sky, the primitive men and women didn't know what the difference was between all the little bright points of light in the sky; they just observed that while most of them moved together (the "fixed" stars) there were several that "wandered" around the sky. They called these lights "wanderers", or in Greek, "planets". The reason that the stars called "fixed" isn't that they do not move, because they DO move. But they are so far away that even a lifetime's worth of movement isn't noticeable.