When you look to the sky you see the past! It’s true, we know that the light travel with 300.000km/s so, when you look to Jupiter for example you see in fact how was Jupiter a half an hour ago, so when you look deeper into the universe, you see the universe in the past, some stars that you see does not exist anymore. It’s a very complex idea, and difficult to understand. Enjoy this documentary film on youtube(5 episodes):

The six billion $ experiment.