- Cycles are fundamental to both natural and human-made systems, ranging from seasons and migrations to economics.
- Milankovitch cycles describe how Earth's orbital variations (eccentricity, obliquity, precession) affect long-term climate and ice age timing.
- Eccentricity (100,000-year cycle) alters Earth's orbit shape, affecting insolation and season lengths, but has a minor annual climate impact.
- Obliquity (41,000-year cycle) changes axial tilt, influencing season severity and ice sheet growth, with current tilt at 23.4° and decreasing.