The amount of incoming solar radiation, also called insolation determines the temperature on Earth. This temperature rises and falls according to the strength of radiation given off by the sun, the distance from the earth to the sun, and the tilt of the Earth's axis of rotation. However, the recent change between glacial and inter-glacial states that occurs on a circa 100,000 year (100 ka) timescale, does not correlate well with these factors. This is known as the 100,000 year problem.