Praetorian guard takes off, departing for light show (6)

I believe the answer is:

aurora

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'light show' is the definition.
(I've seen this in another clue)

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for aurora that I've seen before include "7 ... borealis, ... lights" , "Polar skies phenomenon" , "Coloured light in the sky" , "Atmospheric phenomenon consisting of bands of light" , "Nature's 11 in the Arctic" .)

I've seen this clue in the Irish Times (Crosaire) and The Irish Times.

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