The scale of the universe

The solar system is the Sun, eight planets, their moons, dwarf planets, asteroids and comets. It is part of the Milky Way galaxy, which contains hundreds of billions of stars. The Milky Way is just one of billions of galaxies in the universe.

Distances in space are so huge that we use the light year: the distance light travels in one year, about 9.5 million million km. Light from the Sun takes about 8 minutes to reach us. The nearest star after the Sun, Proxima Centauri, is about 4.2 light years away. When we look at distant stars, we see light that left them long ago, so we are looking back in time. Scale models help: if the Sun were a football, the Earth would be a peppercorn about 25 m away.