Stargazer's delay over current constellation (7)
I believe the answer is:
galileo
'stargazer's' is the definition.
(Galileo Galilei)
'delay over current constellation' is the wordplay.
'delay' becomes 'lag' (lag is a kind of delay).
'over' says the letters should be written backwards.
'current' becomes 'i' (symbol for electric current).
'constellation' becomes 'leo' (Leo is an example).
'lag' reversed gives 'gal'.
'gal'+'i'+'leo'='GALILEO'
(Other definitions for galileo that I've seen before include "Famous scientist" , "US unmanned space-craft launched in 1989 to investigate Jupiter" , "Pioneer scientist" , "It. C 16 to 17 astronomer" , "Great Italian astronomer and physicist of 17th century, suppressed by Church" .)