On 22 or 23 September, the sun shines directly on the equator and the length of day and night are nearly equal in all parts of the world.
This day is known as the autumnal equinox.
The Reason for the Seasons
Many people think that some parts of the year are hotter because we're nearer to the Sun, but the real reason is that the Earth is wonky (tilted).
Why do we have seasons?
We have seasons because the earth is tilted (wonky) as it makes its yearly journey around the sun.
The Earth's tilt
The Earth's axis is tilted at an angle of 23.5 degrees. This means that the Earth is always "pointing" to one side as it goes around the Sun. So, sometimes the Sun is in the direction that the Earth is pointing, but not at other times. The varying amounts of sunlight around the Earth during the year, creates the seasons.
The tilt of the Earth's AXIS is the most important reason why seasons occur.
We have hot summers and cold winters because of the tilt of the Earth's axis.
The tilt of the Earth means the Earth will lean towards the Sun (Summer) or lean away from the Sun (Winter) 6 months later. In between these, Spring and Autumn will occur.
The north pole begins to move away from the Sun. The Sun rises lower in the sky so the days start getting shorter. When the Sun is at its mid-point in the sky, we reach the 'autumn equinox', around 22 September. Day and night are both 12 hours long and its the beginning of autumn.