* Light travels at a finite speed: Light doesn't travel instantaneously. It takes time for light to reach us from distant objects. The speed of light is incredibly fast (approximately 299,792 kilometers per second), but even at that speed, it takes time to cross vast distances.
* The further away an object is, the further back in time we see it: If a star is 10 light-years away, the light we see from it today left that star 10 years ago. Similarly, if a galaxy is millions of light-years away, the light we see from it left millions of years ago.
Example: When we look at the Andromeda Galaxy, which is about 2.5 million light-years away, we are seeing it as it was 2.5 million years ago.
This means we are essentially looking into the past when we observe distant astronomical objects. It's a fascinating concept that allows us to study the evolution of the universe and the objects within it.
