All, ie, go off to an Italian astronomer (7)
I believe the answer is:
galileo
'an italian astronomer' is the definition.
(I've seen this before)
'all ie go off' is the wordplay.
'off' is an anagram indicator.
'all'+'ie'+'go'='alliego'
'alliego' with letters rearranged gives 'GALILEO'.
'to' acts as a link.
(Other definitions for galileo that I've seen before include "victim of Inquisition" , "US unmanned space-craft launched in 1989 to investigate Jupiter" , "Great Italian astronomer and physicist of 17th century, suppressed by Church" , "Italian astronomer and mathematician, d. 1642" , "Great Italian astronomer, a founder of modern science" .)