 The Earth's orbit around the Sun varies in a number of ways that impact the amount of solar radiation and its distribution on the Earth's surface. This variation is cyclical, meaning that over a number of years, the parameter increases and decreases in a periodic fashion. The orbital parameters can be observed in a number of paleoclimate records ranging from the waxing and waning of ice sheets to paleotemperature records. The first orbital parameter is known as eccentricity. This has a cycle of 400,000 years and 100,000 years and describes the shape of the Earth's orbit around the Sun, which varies from a shape that's more elliptical to less elliptical. The second orbital parameter is known as obliquity. It's also known as tilt. And this parameter has a periodicity of 41,000 years and it describes the tilt of the Earth's axis as it circles the Sun. The third parameter is known as procession. Procession has a periodicity of 23,000 years and procession describes the time of year at which the Earth is closest to the Sun and furthest away from the Sun. All three parameters describe the amount and distribution of solar radiation received at any point on the Earth's surface.