Four seasons - solstices and equinoxes
This simulation shows how the 23.5 degrees tilt of the Earth's rotation to the plane of its orbit around the Sun gives rise to the seasons:

June 20-21 solstice: North pole is tilted towards the Sun Summer in north - longest day Winter in south - shortest day Continuous day-light north of the arctic circle Continuous night south of the antartic circle Sun directly over the tropic of cancer	September 22-23 equinox: Both poles receive the glancing rays of the Sun along the horizon Equal nights and days everywhere Autumn in north - days getting shorter Spring in south - days getting longer Sun directly over equator
December 21-22 solstice: South pole is tilted towards the Sun Winter in north - longest day Summer in south - shortest day Continuous night north of the arctic circle Continuous day-light south of the antartic circle Sun directly over the tropic of capricorn	March 20-21 equinox: Both poles receive the glancing rays of the Sun along the horizon Equal nights and days everywhere Spring in north - days getting longer Autumn in south - days getting shorter Sun directly over equator

Within any of our lifetimes the direction of the Earth's spin axis remains fairly constant (it actually prececes like a top - but slowly - completing one full turn every 26000 years) so it's the position of the Earth in its orbit around the Sun that determines the seasons.

The positions of the Tropics of Cancer and Capricon (23.5 degrees either side of the equator) and of the Arctic and Antarctic Circles (23.5 degrees from the poles) directly match the Earth's tilt.