Our galaxy, the Milky Way, is a standard galaxy. Its size, from the light that we receive of it, tell us that it is , que mide de 100 000 light-year wide (1 light-year= 9,46 × 10¹² km). It has more than 200 000 millons of stars. The Sun is one of these stars and it is located in one of he spiral arms of the galaxy, as is shown in the Figure.

The Sun is a normal star, compared to all the other existing stars. Depending on the mass when a star is delivered the rest of its life is defined. Yes, the star evolve in time and that is why we said that they have a life ;o)

But let's star from the beginning and try to find out what is the information behind the colours of the stars when we look at a constellation like Orion, in the picture.