Earth and Environmental Science 11–12 · Year 12
Milankovitch cycles by hand: modelling eccentricity, tilt and precession
Module 7: Climate Science
The idea
Slow changes in the Earth’s orbit and axis redistribute sunlight between seasons and hemispheres over tens of thousands of years, pacing the ice ages.
What you need
- a lamp as the Sun, a globe or ball on a tilted axis, string and two pins for an elliptical orbit
- Earthlearningidea Milankovitch by hand sheet; the NASA Milankovitch page for the cycle lengths
How to do it
- Walk the globe around the lamp on a near-circular path and note the seasons from the tilt; then walk an ellipse and note where the globe is closest to the lamp.
- Change the tilt from 22.1 to 24.5 degrees (the range NASA gives) and observe how far the polar region tips toward the lamp in summer.
- Rotate the direction of the tilt (precession) so the northern summer falls at the near point of the ellipse, then at the far point.
- Record the three cycle lengths from NASA: eccentricity about 100 000 years, obliquity about 41 000 years, precession about 23 000 years on average.
- State which combination gives the coolest high-latitude northern summers and why that favours ice-sheet growth.
What you should see
Greater tilt makes the summer hemisphere face the lamp more squarely; precession shifts which season falls at the near point; eccentricity sets how much the near and far points differ. The learner can state the three periods and the combination (low tilt, northern summer at the far point) that yields cool northern summers.
What changes
This activity lists no variables to change, measure and keep the same.
Common misconceptions
Each of these ideas is wrong, and the activity is a chance to test it.
- Ice ages happen because the Sun gets weaker.
- Orbital cycles explain the warming since industrialisation began (they act over tens of thousands of years).
Safety card
Hazards
- hot lamp
Controls
- lamp on a stand
Note
No hazardous chemicals or heat sources: record the activity in the school's RiskAssess risk assessment, following the NSW Department of Education Science safety and compliance page; the Chemical Safety in Schools package is not triggered.
Curriculum references
The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.
- Earth and Environmental Science Stage 6 Syllabus (2017), NESA; current, replaced by the 11–12 Syllabus (2025) from 2028EES12-14EES11/12-1EES11/12-6EES11/12-7
- Earth and Environmental Science 11–12 Syllabus (2025), NESA; to be implemented from 2028, not yet taughtEES-12-03
- Australian Curriculum v9No Australian Curriculum v9 code is listed.
Sources
The pages the author read to write this activity.