Celestial circuit or part thereof? (5)

I believe the answer is:

orbit

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'celestial circuit' is the definition.
(I've seen this in another clue)

'or part thereof?' is the wordplay.
'part thereof?' becomes 'bit' (both mean a piece of something. I am not sure about the 'thereof?' bit.).
'or'+'bit'='ORBIT'

Can you help me to learn more?

(Other definitions for orbit that I've seen before include "Sphere of activity" , "Circle - influence" , "Circling path" , "Path of a planet or satellite" , "Circumgyration" .)

I've seen this clue in the Evening Standard.

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