Celebration for planetary transit over a grid, perhaps (5,4)
I believe the answer is:
mardi gras
'celebration' is the definition.
(Mardi Gras is an example)
'planetary transit over a grid perhaps' is the wordplay.
'planetary transit' becomes 'maras' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'over' is an insertion indicator.
'perhaps' indicates an anagram.
'grid' anagrammed gives 'digr'.
'maras' placed around 'digr' is 'MARDI GRAS'.
'for' is the link.
Can you help me to learn more?
(Other definitions for mardi gras that I've seen before include "festive occasion" , "Shrove Tuesday celebration" , "Revelry celebrating Shrove Tuesday" , "Shrove Tuesday carnival" , "Time for carnival" .)