These ideas reinforce the copernican revolution we are not the center of the universe. Cosmic address: planet in our solar system, solar system in our galaxy, our galaxy in local group, local group in the local super-cluster, all a part of the universe. Light year (ly) is the distance a photon of light will travel in a year 9. 46 x 10^12km. Alpha centauri: closest star system would take 4. 3 ly to get to 50 000km/h and 100 000 years. Orion nebula (m42: 1500 ly away seeing the nebula are is was 1500 years ago. Milky way is 100 000 ly across and home to about 200 billion stars and dark matter. The more massive the galaxy, the stronger its gravity and the faster stars should be orbiting: by studying stellar orbits, astronomers have put together a map of the distribution of matter in the milky way. The universe contains: all the matter and energy in existence, planets, stars, etc.