All the light you see

We think of light as something immediate. Flip a switch, and it appears in an instant. Yet light travels at a certain speed and takes time to reach our eyes. It's so fast that we don't notice it.  

When we look at stars, the vast distances make this delay obvious. The light we see may have left thousands of years ago, from stars that might no longer exist. In other words, all the light you see is from the past.