A diagram describing the astronomical variations known as the Milankovitch Cycles that have played a chief role in causing the glacial and interglacial periods of the current Ice Age: (P) the precession of the equinoxes, caused by changes in the earth’s axial tilt direction with respect to its orbit around the sun on a cycle of 19,000 to 24,000 years; (T) the earth’s obliquity, caused by changes in the tilt of the earth’s axis with respect to the plane of the ecliptic on a cycle of 41,000-year cycle; and (E) eccentricity, caused by the change in the shape of earth’s orbital path about the sun on a cycle of 100,000 years.