What is the difference between a planet and a star?

What is the difference between a star and a planet?

• Answer:

  The short answer: A star is a massive nuclear reactor floating in space, a planet is a smaller rock or gas ball that commonly orbits a star. The detailed answer: To fully understand the difference between a star and a planet, one must first understand what each is. A star is a mass of chemicals large enough to sustain a stable fusion reaction. Stars are usually composed mostly of hydrogen, deuterium, tritium, helium, and lithium. The older the star, typically, the more variety in elements it contains. Because they conduct nuclear fusion, stars emit massive amounts of electromagnetic radiation (light). The wavelengths (and type) of the light released by a star largely depends on its composition, which is why stars change color with age. There are several common misconceptions about stars, including that they are on fire, that they are static, and that they are small beads of light. The first one is understandable, since stars emit light and heat, and so does fire. However, stars produce their light through nuclear fusion, not combustion. The second misconception is largely derived from the erroneous belief that stars are the largest single objects in space. However, stars often orbit eachother, black holes, quasars, pulsars, and other objects. Even lone stars often move. The third misconception, that stars are small, is simply derived from perspective; from Earth, the sun (a 'sun' is a star with a solar system orbiting it) appears to be much smaller than Earth. However, that is simply due to the relatively large [from our perspective] distance between Earth and Sol (the name of our sun). Unlike a star, a planet is usually relatively cool and stable, and much smaller. Planets may be small, rocky bodies, such as terrestrial planets, dwarf planets, and asteroids (minor planets). They may also be larger, and composed of gases and ice, such as gas giants and ice giants. However, it is true of all planets that they are massive enough to influence the balance of gravity in a system, and large enough, usually, to attain hydrostatic equilibrium, but not large enough for the planet's pressure due to mass to initiate a fusion reaction. Planets, being less massive, often orbit stars, forming solar systems. Planets are therefore commonly the natural satellites of stars, just as moons are the natural satellites of planets. There are sometimes cases in which a star may be similar to a planet, and vice versa. For example, a gas giant, a very large planet comprised mostly of gases, often of composition to said planet's parent star, upon accumulating enough mass, may initiate fusion and become an infant star (it has been theorized that if Jupiter were to gain 40 times its current mass, it could become a star). There is also a class of stars, termed Brown Dwarves, that are very small and cool, and are very similar to gas giants.