It is just the fact that the forward tilt axis (of the North pole) is always along one straight line, while the Earth is going around the Sun in a roughly circular path.
(It; is; just the fact that the forward tilt axis (of the North pole) is always along one straight line) (the forward tilt axis (of the North pole; is; T:always; along one straight line; T:while the Earth is going around the Sun in a roughly circular path)
It the forward tilt axis (of the North pole
is is
just the fact that the forward tilt axis (of the North pole) is always along one straight line
T:always along one straight line T:while the Earth is going around the Sun in a roughly circular path