Design of hat peculiar, an arrangement light years away (5,8)
I believe the answer is:
alpha centauri
'arrangement light years away' is the definition.
(star system light years away from Earth)
'design of hat peculiar an' is the wordplay.
'design of' indicates anagramming the letters (I've seen this in other clues).
'hat'+'peculiar'+'an'='hatpeculiaran'
'hatpeculiaran' with letters rearranged gives 'ALPHA CENTAURI'.
(Other definitions for alpha centauri that I've seen before include "Brightest star in Centaurus" , "Sun's closest star system" , "Bright southern star" , "Bright star near to the sun" , "triple star?" .)