The sheer size and scale of the Universe is something that fascinates me as a budding amateur astronomer. I think of the distances I travel on Earth as being big (I live in the UK so actually they are not that big!), maybe a few hundred miles or so, but these are just microscopic on the scale of the Universe.
To show you what I mean you first need to appreciate that light has a fixed speed of approximately 300,000 km per second and that nothing can travel faster than light. This was first proposed by Einstein and has since stood up to every experiment that has tried to prove or disprove it. You may also be familiar with one of his most famous equations E=MC^2 which dictates that nothing can travel faster than light.
Okay, now you have that concept in your minds let me expand the discussion to the Solar System. The Sun is at the centre of our Solar System and all the planets orbit around it. The Sun is 149,598,000 km away from us on average and as light has a fixed speed it takes 8.23 minutes to reach us from the Sun. In effect we are looking back in time and seeing the Sun as it was 8.23 minutes ago. Taking this a step further everything we look at is in the past as it takes light a small amount of time to travel to your eyes.
Moving out from out Solar System to the Milky Way, our home Galaxy, things get a bit bigger. To measure the distance from one side of the Milky Way to the other we need to use a different unit of measurement called the light year. This is literally what it says on the tin, the distance it takes light to travel in a year, which is 9.4605×10^15 metres (9,460,500,000,000,000 metres). The Milky Way is approximately 160,000 light years in diameter and our Solar System is located about 26,000 light years from the centre.