How can astronomers know things for certain since they only look at space from one vantage point?

Question: How can astronomers know things for certain since they only look at space from one vantage point?
- Keywords:
  astronomer,
  certain,
  space
Asked by Mason The Amazing :) to Andrew, Hina, Ian, Kathryn, Leah-Nani, Xu on 14 Jun 2018.
- Kathryn Burrows answered on 14 Jun 2018:
  
  They don’t! I am sure there is so much more we could learn from travelling through space! However, through the scientific method astronomers have shown that with a lot of hard work and determination, and a little creativity we can figure out an awful lot about the universe even from one small vantage point.
- Andrew Margetts-Kelly answered on 20 Jun 2018:
  
  There is only a certain amount of the universe that we can see. Some is obscured by the Milky Way and by other galaxy, some is just too far back in spacetime to ever witness.
  Because of this we need to extrapolate from what we can see and then make our best guess at the bits we can’t see.

Question: How can astronomers know things for certain since they only look at space from one vantage point?