Topic summary
Earth's axis
Extracted from the Wikipedia article Axial tilt.
Seasons
Earth's axis remains tilted in the same direction with reference to the background stars throughout a year (regardless of where it is in its orbit) – this is known as axial parallelism. This means that one pole (and the associated hemisphere of Earth) will be directed away from the Sun at one side of the orbit, and half an orbit later (half a year later) this pole will be directed towards the Sun. This is the cause of Earth's seasons. Summer occurs in the Northern Hemisphere when the North Pole is directed toward and the South Pole away from the Sun. Variations in Earth's axial tilt can influence the seasons and is likely a factor in long-term climatic change(also see Milankovitch cycles).