Yes, we can!  Light isn’t infinitely fast, it takes time to travel. So that means when you look up at a star in the sky, you are looking at the light that star emitted years ago!

Astronomers use a unit of distance called a “light year,” which is the distance light travels in one year (1 light year = 9,400,000,000,000 km). One of the closest stars to us, Alpha Centauri, is about 4 light years away from the Earth. So if you can find Alpha Centauri in the sky (weather and stargazing location permitting), you are actually seeing what the star looked like 4 years ago. If it suddenly disappeared one day, we wouldn’t know for 4 years!

If you used a very powerful telescope to peer as FAR away into space as you could, you would observe light that has traveled very far and over a VERY long time to reach you. That is what NASA’s James Web Space Telescope (JWST) does– it can observe some of the oldest galaxies in the universe this way.  The picture below shows a galaxy field imaged by JWST. The “red blob” in the zoom-in is GN-z11, one of the oldest galaxies astronomers know about. The light JWST observed is BILLIONS of years old!