* Light travels at a finite speed: Light travels at approximately 299,792,458 meters per second (186,282 miles per second).

* Stars are very far away: Even the closest stars are light-years away. A light-year is the distance light travels in one year.

* The further the star, the older the light: If a star is 10 light-years away, the light we see from it left that star 10 years ago. If a star is 100 million light-years away, the light we see is 100 million years old.

Examples:

* Proxima Centauri: The closest star to our Sun is about 4.24 light-years away. The light we see from it today left the star 4.24 years ago.

* Andromeda Galaxy: This galaxy is about 2.5 million light-years away. The light we see from Andromeda is 2.5 million years old.

Note: When we look at distant stars, we're essentially looking back in time. The light we see tells us what those stars looked like millions, billions, or even trillions of years ago.