Astronomer Fred needs year inside crater (5)
I believe the answer is:
hoyle
'astronomer fred' is the definition.
(English astronomer Fred Hoyle)
'year inside crater' is the wordplay.
'year' becomes 'y'.
'inside' indicates putting letters inside.
'crater' becomes 'hole'.
'y' placed within 'hole' is 'HOYLE'.
'needs' is the link.
(Other definitions for hoyle that I've seen before include "English author, expert on card games, d.1769 - English astrophysicist, d. 2001" , "Sir Fred(erick) -, British astronomer" , "Edmond --, early writer on card games" , "English writer on card games" , "English astrophysicist, who coined the term "big bang", d. 2001" .)