Why does the tilt of the earth affect the amount of light and therefore the seasons? How are the seasons affected by the tilt of the equator?

1 Answer
May 14, 2017

The axial tilt dictates how much of the Sun's radiation is received by each hemisphere.


First of all the Earth's axial tilt angle and direction are constantly changing due to precession. These effects are small and are only noticeable over long periods of time. We will ignore theses effects in this discussion.

The Earth's axis of rotation makes an angle of about 23.5 degrees to the ecliptic - the plane of the Earth's orbit. The axis always points in the same direction with respect to the fixed stars. It has to because of the law of conservation of angular momentum.

At any moment of time half of the Earth is in direct sunlight.

At the March and September Equinoxes, the Sun is directly over the equator. This means that both the Northern and Southern hemispheres get equal amounts of sunlight. At these times the days and nights are of almost equal length.

At the June and December Solstices, the Sun is directly over the tropic of Cancer or the tropic of Capricorn. This means that one arctic region has a 24 hour day and the other a 24 hour night.

The areas between the tropics always have equal length days and nights. The areas between the tropics and arctic circles have longer days and shorter nights or vice versa.

This is the basic reason for the seasons. There is a lag while the Earth cools or warms so the warmest Summer days and the coolest Winter days are in July/August and January/February in the North and the opposite in the South.