There's a curious thing about looking up, especially
if you happen to be looking up at a clear, dark night sky - you can literally see into the past! Now, this applies to things in the sky other than clouds and bats - things like stars, planets, and galaxies.
But before we get to the crux of the matter, you have to realize that
light travels at about 186,000 miles (300,000 km) per second - that would be about 7 times around the Earth in one second. Now, that's pretty fast, but not infinetly so. And since the distances we are considering are significantly greater than 186,000 miles, you can see that it is going to take time for light to travel those immense distances.
The Moon is about 240,000 miles (384,00 km) away. Divide that by 186,000 and you get the appromately 1.3 seconds that light takes to travel from the Moon to Earth. So that means
whenever you look a the Moon, you are seeing it as it was 1.3 seconds ago. Well, that's not so bad, you say? Harumpn, Big deal!
But it gets better, really!
When you look at the Sun, you are seeing it as it was about 8 minutes ago. Do the math: 93,000,000 miles (distance from Earth to the Sun) divided by 186,000 (speed of light per second) = 500 seconds = about 8.3 minutes. Keep in mind that the light you see Now actually left the Sun about 8.3 minutes ago and is just now getting to your eyes. So, when you see the Sun rise, it actually rose 8.3 minutes ago. And
if the Sun were to suddenly go supernova, we wouldn't know it until 8.3 minutes later because the light from the supernova event would take over 8 minutes to get here.
But we're not going to stop here,... because it just keeps getting sooo much better.