It’s a story about us
When you look up at the stars at night, you are reading the story of the cosmos.
Light travels at 300,000 km/s (186,000 mps) in the vacuum of space. The distance light travels in one year is called a light year, which is 9,500,000,000,000,000 km. That means that it takes a ray of light a whole year to travel that far.
Think about the implications. Proxima Centauri, the closest star to our sun, is 4.2 light years away. So, if Proxima Centauri were to suddenly explode, we would not know for 4.2 years, since nothing travels faster than light, and we need the light to know that it happened!
But that’s just the closest star. The closest galaxy, Andromeda, is 2,530,000 light years away. So it would take 2,530,000 years for us to know that something happened to Andromeda.
But that’s only the closest galaxy! There are something like 100,000,000,000 galaxies in the universe, and all of them are farther away than that, and so it takes light that much longer to reach us!
So when you see the Andromeda galaxy in the sky, you are seeing it the way it looked 2,530,000 million years ago. You are looking at the history of the cosmos. But it’s not just the history of the cosmos. We came from the cosmos. Every atom in your body was cooked in the center of a star that eventually exploded. The story of the cosmos is the story of us.