updated aoi definition #2247

Author: RDaxini

docs/sphinx/source/user_guide/glossary.rst

@@ -21,7 +21,8 @@ There is a convention on consistent variable names throughout the library:
         [unitless]
 
     aoi
-        Angle of incidence between :math:`90\deg` and :math:`90\deg`
+        Angle of incidence. Angle between the surface normal vector and the
+        vector pointing towards the sun’s center
 
     aoi_projection
         cos(aoi)