I have always been bothered by this question and cannot figure it out and cannot phrase a google search to get an answer.
This is going to be rough, I will try not to use any numbers.
Photons have infinite range, of course limited by how much time you have on your hands. So every second we can see that much farther into the universe. That makes a goodly amount of sense to me.
What I don't understand is how we can see stars at all. I really enjoy looking at them, but do not understand how they can be seen over vast distances.
If a star throws out a finite number of photons, distributed in a finite volume, then there must be a threshold that you cannot resolve a star. (I do hear that people can see a single photon, but I firmly believe stars appear to be bigger than a single photon. Even dust would mask everything that small anyway.)
It seems like the volume of space involved with interstellar distances should reach this threshold of visibility very quickly. Star emit vast quanities of photons a second, but really, is the number of photons emitted so large that even interstellar volumes of space do not "swallow" them up?
Speaking in terms of photons, it strikes me (no pun intended) that a star doesn't have the output to cover all of the space/angles to allow for resolving them. It is easy to picture a child's drawing of the sun with a person standing between the rays. That person would not see the sun becuase they are "between the photon's paths." Or maybe that should read "between the crayon's paths." : )
Even when I "quit" the idea of photons, and switch to waves, it is boggling to think our sun has enough power to allow it to be as clearly visible as it is. Shouldn't it appear grainy or "wavey?"
What am I missing?