What are the factors that cause the occurence of seasons?
The Earth is tilted on its axis. Summer occurs when one hemisphere, either the northern hemisphere or the southern hemisphere, is tilted towards the Sun and thus receives more direct sunlight.
A common misconception is that the seasons have to do with the Earth being closer to the Sun due to the elliptical nature of its orbit, which is not the case. The Earth in fact is closest to the Sun in the beginning of January and furthest away the first week of July.
The Earth spins about its axis at a fixed angle (about 23,5 degrees) to the plane of its orbit. Depending on the planet’s orbital position, either northern or southern latitudes can receive both longer hours of daylight and more direct radiation (i.e. at an angle to the atmosphere closer to perpendicular).
Twice during the year (spring and fall Equinox – around the 20th of March and September respectively), the Sun appears to circle more directly over the equator, and most areas of the globe receive similar amounts of daylight (the poles are exceptions with extremely long periods of the sun either above or below the horizon. From late December to late March, the Southern Hemisphere experiences summer while the Northern Hemisphere experiences winter. From late June to late September, the position is the other extreme, and it is summer in the Northern Hemisphere, winter in the Southern.
These yearly changes in insolation (energy from the sun falling on the Earth) cause the seasons, in conjunction with the prevailing directional wind patterns, ocean areas, currents, and pressure systems.
