Their performance is out of this world (5)

I believe the answer is:

stars

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

'their performance' is the definition.
I know that 'performance' relates to this answer.

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for stars that I've seen before include "Leading actors" , "plays a leading role" , "Heavenly bodies" , "Horoscope (colloq.)" , "''What is the ...? What is the ...? '' (Juno and the Paycock)" .)

I've seen this clue in the Evening Standard.

Want a hint initially instead of a full solution? Install my app