Light starts to leave all stars, every rotation (5)
I believe the answer is:
laser
'light' is the definition.
(lasers are a type of light)
'starts to leave all stars every rotation' is the wordplay.
'starts to' suggests taking the first letters.
The initial letters of 'leave all stars every rotation' is 'LASER'.
(Other definitions for laser that I've seen before include "Source of light; type of printer" , "Device yielding powerful beam" , "Device producing a narrow, intense beam of light" , "modern light industry" , "Source of intense beam" .)