A Milankovich cycle is any slow but regular change in the Earth's orbit around the Sun, and the tilt of the Earth's axis.[1]
The dynamics are complex. The changes affect the 'insolation' (sunlight falling on parts of the Earth). This leads to cycles of climate on Earth, at about 21,000, 41,000 years, 100,000 and 400,000 years. This whole field is still under active research.
Using applied mathematics, Milutin Milanković predicted that variations in eccentricity, axial tilt, and precession of the Earth's orbit caused climate patterns on Earth.
Similar astronomical theories had been advanced in the 19th century by Joseph Adhemar, James Croll and others. However, there was at first no reliable dated evidence. The issue was not settled until deep-ocean cores were taken and a paper published in Science in 1976.[2]