Star that’s behind Aries lit up sky briefly (8)
I believe the answer is:
asterisk
'star' is the definition.
(synonyms)
'that's behind aries lit up sky briefly' is the wordplay.
'behind' says to take the final letters.
'lit up' indicates an anagram (lit up can mean drunk).
'briefly' means to remove the last letter.
The final letter of 'that' is 't'.
'sky' with its final letter taken away is 'sk'.
't'+'aries'='taries'
'taries' anagrammed gives 'asteri'.
'asteri'+'sk'='ASTERISK'
(Other definitions for asterisk that I've seen before include "Star on a page" , "Sign" , "Star-shape on the page" , "Sarkiest (Anag)" , "Printer's star" .)