The Solar System: summary

A few of the things that we have learnt about the Solar System:
  • planets are celestial bodies that do not emit their own light, they just reflect that of the Sun: the stars, instead, are light sources.
  • the Sun is the only body in the Solar System that emits light (that is, it is the only star). 
  • the Sun stays at the center of the Solar System. It contains most of the mass of the Solar System, 99%. Around the Sun, all planets, asteroids and comets orbit. 
  • the orbiting of a body around another is a universal phenomenon, only depending on the mutual gravitational attraction, not on the kind of body or the intervening medium. 
  • the laws of orbital motion (that is the three Kepler's laws) hold for every Solar System body: planets, comets and asteroids. 
There can be other planetary systems like ours, in the cosmos. Scientists think that some of these hypothetical planets, called "extra solar", could also host some forms of life, but it is premature to think about a close encounter with those hypothetical "tiny green men"... 
Among all the planets in our Solar System, the Earth is the only one which is suitable to host a form of life like the one we are used to. In fact, it requires the presence of water, oxygen and carbon compounds. Moreover, the temperature of the planet must be high enough so that liquid water can exist on its surface, and low enough so that the water does not evaporate. 

In order to discover the stars, you will have to patient a bit longer. We must first learn something about the light : the password for that lesson is "draco".