Eclipse increases thanks to gravitational constant energy (7)
I believe the answer is:
upstage
'eclipse' is the definition.
(I've seen this before)
'increases thanks to gravitational constant energy' is the wordplay.
'increases' becomes 'ups' (upping is a kind of increasing).
'thanks' becomes 'ta' (UK informal version of 'thank you').
'to gravitational constant energy' becomes 'ge' (I can't explain this - if you can you should believe this answer much more).
'ups'+'ta'+'ge'='UPSTAGE'
Can you help me to learn more?
(Other definitions for upstage that I've seen before include "Furthest from the audience (in theatre)" , "(Of actor) away from the audience" , "Be haughty towards" , "Outdo" , "Take the limelight from" .)