Axis Tilt is Critical for Life. The tilt of the Earth's spin axis with respect to the plane of its orbit about the sun (the ecliptic plane) is important for a habitable Earth. The Earth's spin axis is tilted 23.5° with respect to the ecliptic, giving moderate seasons and preventing temperature extremes anywhere on the planet. This illustration, patterned after Ward and Brownlee, summarizes the effects of different tilt angles with respect to the ecliptic plane.