Oh excellent question! This actually has to do with the earth being round! Because of this we can only see as far as the horizon!
answered on 28 Apr 2020:
last edited 28 Apr 2020 2:17 pm
Great question! It depends on what you’re looking at really, and how bright it is.
So like Sonia said, we won’t be able to see anything beyond the horizon on earth, as the planet is round, and the earth gets in the way.
But, if you look up at the moon or the stars, for example, we can see them clearly and they’re very far away. So I think the answer is that we can see things incredibly far away if they’re bright enough. We just need enough light from them (photons) to reach our eyeballs. 🙂
In 1941, a scientist named Hecht did an experiment and worked out that we only need about 50 to 100 photons to reach our eyes for us to see a flash of light, depending on how sensitive your eyes are. This explains why we can see starts that are trillions of miles away!