I’ve always wondered how astronomers can actually observe galaxies that are millions or even billions of light-years away. What exactly are we seeing when we look at them?
And when scientists say there are hundreds of billions, or possibly trillions, of galaxies in the observable universe, how do they know that if we obviously haven’t seen and counted every single one?
We see the galaxies as they were however many years it took for the light to reach us.
Every time we look, we find something new because there’s both a LOT of stuff in space and because light from further away keeps eventually reaching us.
…but mostly it’s a very complicated guess with a lot of math based on what we’ve already seen. Truth is, we don’t know precisely how many galaxies there are, but there’s always a whole shit ton of them everywhere we look, so it’s reasonable to assume the number is pretty big. And getting bigger because, again, we keep seeing new stuff.