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

It’s worth noting that many telescopes do not, and need not, see super far, as in zooming-in. What they do is drastically increase aperture. This means being able to see very dim things.

When you look up into the sky at the moon, realize that for example, that the andromeda galaxy takes up about 6x the width across as the moon in the sky. The reason you can’t see it up there, being larger in the sky than the moon, is because it’s very dim.

objects like this are emitting light equally in intensity in all directions. Your perception of its brightness is dictated by the amount of that light that goes into your pupil. When you look through a visual telescope with an aperture of 24 inches, you’re effectively making your pupil 24 inches in diameter, funneling all of that light into your small pupil. This allows you to see much more dim things.