how did you find out how big our universe is if astronauts have never been to the end of it?

Question: how did you find out how big our universe is if astronauts have never been to the end of it?
- Keywords:
  size,
  space,
  universe
Asked by anon-225889 to Sameed, Jose, joannabarstow, Heidi, Freya, Chris on 19 Nov 2019. This question was also asked by anon-225898.
- Joanna Barstow answered on 19 Nov 2019:
  
  You can see much further in the Universe than the distance an astronaut could get to, but we still can’t see the edge of the Universe. We have no evidence our Universe has an edge, so we don’t actually know how big it is.

Question: how did you find out how big our universe is if astronauts have never been to the end of it?