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We can look back in time !?

Sophia Xu
Updated: September. 10, 2023 

 Have you ever wondered how far you can see when you look up at the night sky? You might think that the stars you see are close to us, but in fact, they are very far away. The distance between us and the stars is so huge that we need a special unit to measure it: the light-year.

A light-year is the distance that light travels in one Earth year. Light is very fast and can go around the Earth seven times in one second. One light-year is about 9 trillion kilometers or 6 trillion miles. That is a 6 with 12 zeros behind it! ( Imagine your bank card has a 6 with 12 zeros behind it )

But why do we use light-years to describe the distance of stars? Because light takes time to travel from one place to another. 

The light that we see from the Sun, for example, left the Sun eight minutes ago. But that doesn't mean the sunlight we see is 8 minutes old. The sun makes light by nuclear fusion. How long does that take ? We will discuss it in another blog post.

The same thing happens with other stars ( not nuclear fusion, the light-year thing )  but on a much larger scale. The closest star to us, Proxima Centauri, is about 4.2 light-years away. That means that the light we see from it today left the star 4.2 years ago. We see Proxima Centauri as it was in 2019, not as it is in 2023. Mind-blowing right!

Some of the stars we see are much farther than that. The Orion nebula, for example, is a beautiful cloud of gas and dust where new stars are born. It is about 1270 light-years away from us1. The light that reaches us today came out of Orion when the Middle Ages had just begun on Earth.

By looking at distant objects in space, we are actually looking back in time. We can see how the universe was in the past, and how it has changed over billions of years. Some of the most powerful telescopes, like the James Webb Space Telescope2, can look at galaxies that are so far away that their light has been traveling for more than 13 billion years3. That is almost as old as the universe itself! We have another blog post talking solely about the James Webb Space Telescope ( JWST )

So next time you look up at the night sky, remember that you are not only seeing stars but also history. But you should also know this beautiful night sky won't last very long. 96% of all the stars that are ever going to be the universe have already been born. 

The universe is constantly expanding and stars like our sun are constantly using energy, and the universe has no way of getting back that energy. Humans have plenty of these dooms day theory. I guess that's why our horror movies are so good.