Brilliant look. Right stuff to set off astronomers (10)
I believe the answer is:
stargazers
'astronomers' is the definition.
('stargazer' can be a synonym of 'astronomer')
'brilliant look right stuff to set off' is the wordplay.
I cannot quite understand how this works, but
'brilliant' could be 'star' (I've seen this in other clues) and 'star' is present in the answer.
'look' could be 'gaze' (gazing is a kind of looking) and 'gaze' is located in the answer.
'right' could be 'r' (common abbreviation) and 'r' is present in the answer.
A single letter 's' remains which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Another definition for stargazers that I've seen is " Astronomers".)