Axis angle is a position angle whose reference (0 deg. point) is the Moon's
axis of rotation, not celestial north. So 0 deg. axis angle marks the lunar
north pole, 90 deg. is its equator on the east side (near Grimaldi), 180 deg. is
the south pole, and 270 deg. is the lunar equator on the west side (near Mare
Smythii). Watts angle is offset from axis angle by a constant 0.2 deg., and is
given on the predicted graze profiles; they are not the same due to a mistake
in the reference point made when Watts' limb correction charts were created.
Return to the