"What would happen if the moon were not there? Then our tilt could swing wildly over a large range, resulting in major temperature swings. If our tilt were more like ninety degrees, the north pole would be exposed to the sun for six months, while the south pole would be in darkness, then vice-versa. Instead, it varies by only about one and a half degrees - just a tiny variation, because the gravity from the moon's orbit keeps it stabilized."