How do telescopes see so far into space? Since celestial bodies are thousands & millions of light years away, How can NASA telescopes capture an image of planets & galaxies that far?

Question

I quite frankly understand the concept of light years and how light has to travel before we (humans on earth) can process that image. For example, the sun that we see in the sky is actually the sun 8 minutes prior to when we were viewing it, because it takes 8 minutes for the light of the sun to travel to earth.

With that, how do these mega-telescopes work (Hubble and James Webb)? And does it mean we’ll never be able to see how planets and galaxies look in present time?

In: 15

Answer 1

The amount of light from very distant objects that reaches us is extremely small, but if you can collect enough of it, you can still produce an image. You achieve that two ways – firstly by having a very large surface capturing the light (the James Webb telescope mirror has a surface are of about 25m^2 ), and secondly by collecting it for a long time (some of the telescope’s exposures have lasted for 6 hours and more). The dimmer the light, the bigger the aperture and the longer the exposure you need. Just like any camera, basically.

(You answered your second question in your first paragraph. We’ll never be able to see what anything out there looks like in present time, simply because the light we capture has to take time to get to us, so we can only ever see things as they were when the light started out. Short of an unimaginably fundamental change in the way that we understand the universe to work, that’s never going to alter.)