Axis tilt · Lean
How Earth’s tilt changes
Obliquity is the tilt of Earth’s axis, measured from the line that stands upright on the orbit’s plane. It swings between about 22.1° and 24.5° in a cycle of 41,000 years. Today it is 23.44° and falling, and the next low comes in about 10,000 years.
About 41,000 years
Axis tilt
The axis leans between 22.1° and 24.5° from upright.
Midsummer daylight
The Sun is up 20.1 hours at 22.1° of tilt and 22.4 hours at 24.5°.
Summer melt
Cooler high-latitude summers let more winter snow survive.
How tilt makes seasons
Seasons come from tilt, not from distance. Earth is closest to the Sun in early January, when it is winter in the north. As Earth goes around, the hemisphere tipped toward the Sun gets longer days and a higher Sun. The other hemisphere gets shorter days and a lower Sun.
A bigger tilt widens that difference. The effect grows with latitude, so the poles feel it most and the tropics hardly at all.
Why it matters for ice
On a midsummer day at 65°N, the daily average sunlight is 457 W/m² at 22.1° of tilt and 496 W/m² at 24.5°. That is a difference of 39 W/m². With less tilt, northern summers are cooler and more winter snow survives. Repeated for thousands of years, that can build an ice sheet, if the rest of the climate allows it.
The same change also moves sunlight between latitudes. It does not simply warm or cool the whole planet.
A small angle with a long reach
The whole range is 2.4 degrees. It works the same way for thousands of years, and feedbacks from ice, oceans and carbon dioxide amplify it.
Tilt always has to be read together with the stretch and the wobble. Together they decide where and when sunlight changes most.
Try it yourself
Change the orbit
Move all three motions and watch midsummer sunlight at 65°N change.
Questions
Quick answers
What is Earth’s tilt today?
23.44°, the standard J2000 reference value. It is slowly decreasing.
Would Earth have seasons without tilt?
Only weak ones. Distance would still change the sunlight a little, but both hemispheres would warm and cool together.