What causes the seasons?

The seasons are a result of the 23.5 degrees of tilt of Earth's rotational axis in relation to its orbit around the Sun. This tilt means that throughout Earth's orbit around the Sun (our calendar year) certain areas of the globe are tilted towards the Sun, while other areas are tilted away from it.

This creates a difference in the amount of solar radiation (or sunlight) that reaches different parts of the Earth, therefore creating the global cycle of fluctuations that we know as the seasons.