P1 - The Universe: Distances and Sizes

P1 - The Universe: Distances and Sizes

1. Distances and Sizes

   • The Sun is one of thousands of millions of stars in the Milk Way
     • The Milky Way is one of thousands of millions of galaxies which make up the Universe
   • Distances to objects outside the solar system are measured in light-years
     • A light year is the distance that light travels in a year.
       • One light year is 9.5 million million kilometres.
   • Light travels through space (a vacuum) at a speed of 3.0 x 3000 000 km/s
     • Light takes a very long time to reach us from the stars.
       • We can only observe what stars were like in the past, when the light left them.