Astronomer's model in error — after switching two bits, okay finally (6)
I believe the answer is:
orrery
'astronomer's model' is the definition.
(an orrery is a model of the solar system)
'error after switching two bits okay finally' is the wordplay.
'after switching' indicates anagramming the letters.
'two bits okay' becomes 'y' (I can't explain this - if you can you should believe this answer much more).
'finally' says to put letters next to each other (some letters go at the end of others).
'error' anagrammed gives 'orrer'.
'orrer'+'y'='ORRERY'
'in' is the link.
(Other definitions for orrery that I've seen before include "Clockwork model of the sun and planets" , "Planetary model" , "Mechanical model of the solar system" , "Err, Roy, on the side of a model of the solar system" , "Planetarium that illustrates the positions and motions of bodies in the solar system" .)