Seasonal variations in polar sunlight, illustration. At the Earth's poles, the angle of incidence of sunlight is reduced compared to at the equator. The effect is more pronounced in winter compared to summer, as shown at right. The Sun at top is at midsummer, at centre it is at the equinoxes (spring and autumn) and at bottom is seen in the middle of winter. At midsummer, the sunlight is spread over a smaller area of surface and a thinner amount of atmosphere compared to other times of the year, so has more of a warming effect. At the equinoxes, the sunlight is spread over a wider area, so is relatively cooler. It is also weakened by passing through a thicker layer of atmosphere. In winter, sunlight does not reach the pole at all.