I always read/hear "This galaxy is X thousand light years away" or some similar statement (for example see this table). Please excuse the naivety of question. How do we determine that some astronomical body is "x" light years away. Surely we don't send light beams and wait for them to come back. :-P
1
-
$\begingroup$ See this question: astronomy.stackexchange.com/questions/92/… $\endgroup$– AaronJul 25, 2014 at 4:34
Add a comment
|