<P> Also in the middle latitudes, the seasonal climate variations produced by changes in the length of daytime are the most marked, with very distinct periods of cold and heat, and other secondary seasonal changes such as snow and ice in winter that disappear in summer and so on . At high latitudes, it is cold most of the time, with constant snow and ice, so the seasons are less obvious; and in the tropics, it is hot most of the time, with no snow or ice at all, so again the seasons are less obvious . </P> <P> The exact instant of solar noon, when the Sun reaches its highest point in the sky, varies with the seasons . This variation is called the equation of time; the magnitude of variation is about 30 minutes over the course of a year . </P>

What happens to the length of day as you move north of the equator