Erratic motion around Lagrange point as revealed by satellite (7)
I believe the answer is:
moonlit
'as revealed by satellite' is the definition.
(the moon is a natural satellite)
'erratic motion around lagrange point' is the wordplay.
'erratic' indicates an anagram.
'around' means one lot of letters goes inside another.
'point' says to take the initial letters (an end or point of the word).
The first letter of 'lagrange' is 'l'.
'motion' anagrammed gives 'moonit'.
'moonit' placed around 'l' is 'MOONLIT'.
(Other definitions for moonlit that I've seen before include "Illuminated by satellite" , "gently enlightened?" , "Gently illuminated" , "Illuminated by night" , "Illumined by Selene?" .)