Clouds in otherwise blue area in northeast (7)
I believe the answer is:
nebulae
'clouds' is the definition.
(I've seen this before)
'otherwise blue area in northeast' is the wordplay.
'otherwise' is an anagram indicator.
'area' becomes 'a' (maths abbreviation).
'in' indicates putting letters inside.
'northeast' becomes 'NE' (abbreviation).
'blue'+'a'='bluea'
'bluea' with letters rearranged gives 'ebula'.
'ebula' put inside 'ne' is 'NEBULAE'.
'in' is the link.
(Other definitions for nebulae that I've seen before include "Cloud-like patches in space" , "Stardust" , "Bright patches in sky from distant galaxies" , "Gas or dust clouds in space" , "where stars are born" .)