Stellar scientist who cannot work under a cloud? (10)

I believe the answer is:

astronomer

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'stellar scientist' is the definition.
'astronomer' can be an answer for 'scientist' (astronomer is a kind of scientist). I am not sure about the 'stellar' bit.

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for astronomer that I've seen before include "scientist" , "Star-watcher" , "Sky-at-night observer" , "Observer of space" , "One studying the universe" .)

I've seen this clue in The Irish Times.

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