How we can 'see' the past

We can 'see' the past by looking up at the night sky and viewing stars  because of the finite speed of light, when you gaze up into the night sky, you are looking into the past. 

Scientists claim that if an alien 65 million light years away sees earth through a powerful telescope, they can see "dinosaurs". How can that be possible?

This question raises the fascinating issue of look-back times. Because of the finite speed of light, when you gaze up into the night sky, you are looking into the past. The bright star Sirius is 8.6 light years away. That means the light hitting your eye tonight has been traveling for 8.6 years. Put another way: 

When you look at Sirius tonight, you see it as it was 8.6 years ago.The bright star Sirius is 8.6 light years away. That means the light hitting your eye tonight has been traveling for 8.6 millions of years. Put another way: 

Scientists claim that if an alien 65 million light years away sees earth through a powerful telescope, they can see "dinosaurs". How can that be possible?

This question raises the fascinating issue of look-back times.