The four seasons are determined by changing sunlight (not heat!) - which is determined by how our planet orbits the Sun and the tilt of its axis.

At the start of spring - The Spring Equinox - day and night are approximately 12 hours long and the Sun is at the midpoint of the sky. Our north pole tilts towards the Sun.

At the Summer Solstice, the longest day of the year, the Sun is at its most northern point in the sky. After this date, the days start getting shorter.

Fall begins at the Autumn Equinox. Day and night are about 12 hours long and the Sun is at the midpoint in the sky. The north pole moves away from the Sun.

The start of winter begins with the Winter Solstice, the shortest day of the year, when the Sun is at its most southern point in the sky. From then on, the days start getting longer.