Tilt & Spin
Thanks to being whacked by its soon-to-be Moon, Earth’s rotational axis tilts at 23.4°. This tilt brought seasonal variations.
The obliquity of Earth – the orientation of its spin axis to solar orbital plane – has changed over time. Even minor changes in obliquity cause major climatic shifts. The tilt of the Earth’s axis as it spins gives rise to the seasons. The aspects of periodicity in Earth’s spatial and orbital changes are known as Milankovitch cycles.
Earth’s shape and spin result in a difference in gravitational pull between the poles and the equator, with equatorial objects lighter by 0.6%. Even at the same latitude, gravity varies from place to place because of several factors, including the bulge about the Earth, elevation, such as mountain ranges, and the moon’s gravitational influence.
Earth’s rotation has a gravitational effect upon itself, causing the diameter at the equator to be 27 km greater than its diameter through the poles.
Earth spins about its axis at a rate of 0.5 km per second. Its revolution about the Sun moves at 30 km/sec.