The seasons are a result of Earth’s axis of rotation being tilted 23.5 degrees with respect to its orbital plane. This means that as the Earth travels around its orbit of the Sun the Northern hemisphere is at times closer to the Sun than at other times of the year. As the Earth orbits on a tilted axis when the Northern hemisphere is closer to the Sun the Southern hemisphere is further away and vice-versa which results in the seasons occurring at opposite times on the year in each hemisphere.

Summer occurs when the tilt it towards the Sun and Winter occurs when the tilt is away from the Sun. Autumn and Spring occur during the passage between these two points. It is interesting to note that the hottest temperatures in the Summer usually fall around a month or so after the point at which the tilt causes a hemisphere to be closest to the Sun. This happens because the Earth and its atmosphere can store a large amount of heat, the oceans being particularly effective heat sinks. This captured heat is then dissipated later in the year.