Question

What causes seasons?

Answer 1

Seasons are caused by a planet's axial tilt.

Explanation:

If a planet's axis of rotation isn't perpendicular to the plane of its orbit it will have seasons. The reason for this is that one hemisphere gets more sunlight than the other for part of the year.

In the case of the Earth, the tilt is `23^@`. This gives us the four seasons. When the axis of rotation is pointing towards the Sun it is Summer. When the axis is pointing away from the Sun it is Winter.

Of the planets in the solar system, Mercury, Venus and Jupiter have small axial tilts and so have little seasonal effect. All of the other planets have seasons.

Uranus with an axial tilt of `83^@` has extreme seasons.