What strains moon explorer joining firm (8)
I believe the answer is:
colander
'what strains moon' is the definition.
I can't tell whether this definition defines the answer.
'explorer joining firm' is the wordplay.
'explorer' becomes 'lander' (I can't justify this - if you can you should believe this answer much more).
'joining' is a charade indicator (letters next to each other).
'firm' becomes 'co' (a firm is a company).
'lander' put after 'co' is 'COLANDER'.
Can you help me to learn more?
(Other definitions for colander that I've seen before include "Culinary strainer" , "Vessel for draining" , "Kitchen sieve" , "implement that's full of holes" , "Perforated vessel" .)