Why do we have seasons?

The reason that we have seasons is that the earth is tilted on it's axis of rotation. This means that at different times of the year the southern hemisphere is pointed towards the sun or away from the sun. In summer the sun's rays hit the surface at a steep angle. The days are longer and the nights are shorter. In winter the sun's rays hit at a shallow angle, the days are shorter and the nights are longer. In the northern hemisphere the seasons are opposite to the southern hemisphere.

A solstice occurs twice a year when the tilt of the earth is most towards or away from the sun. The summer solstice is the longest day of the year and the winter solstice is the shortest day of the year. The equinox is when the day and night are equal in length.