Star beginning to undertake a month in South Africa (9)
I believe the answer is:
supernova
'star' is the definition.
(supernova is a kind of star)
'beginning to undertake a month in south africa' is the wordplay.
'beginning to' indicates taking the first letters.
'a' becomes 'per'.
'month' becomes 'nov' (Nov is an example**).
'in' is an insertion indicator.
'south africa' becomes 'sa' (abbreviation).
The first letter of 'undertake' is 'u'.
'u'+'per'+'nov'='upernov'
'upernov' inserted inside 'sa' is 'SUPERNOVA'.
(Other definitions for supernova that I've seen before include "Star in decline" , "Exploding star that becomes extremely luminous" , "Star made brilliant by stellar explosion" , "cosmic explosion" , "it puts an end to a starry career" .)