Post-sunset radiance (9)
I believe the answer is:
afterglow
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">post-sunset radiance</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for afterglow that I've seen before include "trace of sunset" , "Light once the actual source has gone" , "The satisfaction" , "Light in the sky post sunset" , "Remaining light" .)