It's affected by Earth's position (4)
I believe the answer is:
site
'position' is the definition.
(I know that site is a type of position)
'it's affected by earth's' is the wordplay.
'affected' is an anagram indicator.
'by' is a charade indicator (letters next to each other).
'earth' becomes 'e' ().
'its' with letters rearranged gives 'sit'.
'sit'+'e'='SITE'
(Other definitions for site that I've seen before include "Location (of building, dig etc)" , "Situation (of a building)" , "Where something is located" , "station" , "Place for building" .)