One may be struck by its unearthly light (4)

I believe the answer is:

moon

I'm a little stuck... Click here to teach me more about this clue!

'light' is the definition.
(I know that Moon is a type of light)

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for moon that I've seen before include "Display one's buttocks publicly (slang)" , "Appear listless" , "drummer?" , "down one's pants" , "Satellite revolving round the earth" .)

I've seen this clue in the Evening Standard.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.