season

The cause of the seasons. As the Earth orbits the Sun, its axis of rotation always points in the same direction. This means that, during the northern hemisphere summer solstice (usually 21 June), the Sun is overhead in the northern hemisphere. At the northern hemisphere winter solstice (usually 22 December), the Sun is overhead in the southern hemisphere.

Period of the year having a characteristic climate. The change in seasons is mainly due to the Earth's axis being tilted in relation to the Sun, and hence the position of the Sun in the sky at a particular place changes as the Earth orbits the Sun.

When the northern hemisphere is tilted away from the Sun (winter) the Sun's rays have further to travel through the atmosphere (they strike the Earth at a shallower angle) and so have less heating effect, resulting in colder weather. The days are shorter and the nights are longer. At the same time, the southern hemisphere is tilted towards the Sun (summer) and experiences warmer weather, with longer days and shorter nights. The opposite occurs when the northern hemisphere is tilted towards the Sun and the southern hemisphere away from the Sun.

In temperate latitudes four seasons are recognized: spring, summer, autumn (fall), and winter. Tropical regions have two seasons – the wet and the dry. Monsoon areas around the Indian Ocean have three seasons: the cold, the hot, and the rainy.

The differences between the seasons are more marked inland than near the coast, where the sea has a moderating effect on temperatures. In polar regions the change between summer and winter is abrupt; spring and autumn are hardly perceivable. In tropical regions, the belt of rain associated with the trade winds moves north and south with the Sun, as do the dry conditions associated with the belts of high pressure near the tropics. The monsoon's three seasons result from the influence of the Indian Ocean on the surrounding land mass of Asia in that area.