eli5: How are we accurately able to study far off cosmic objects if our primary source of information is from light (that sometimes has traveled to us for 1000’s of years). Am I missing something?

Question

eli5: How are we accurately able to study far off cosmic objects if our primary source of information is from light (that sometimes has traveled to us for 1000’s of years). Am I missing something?

In: 8

Answer 1

OP, is your question “how can we know what the current state of a star is if we’re seeing light emitted centuries ago”?

If so: we can’t. When we say “X is a blue supergiant”, what we mean is “X was/is a blue supergiant, as of the era in which we are able to observe it”.