1. Tilt of the Rotational Axis:

* Planets don't spin perfectly upright. Their rotational axis (the imaginary line around which they spin) is tilted at an angle.

* This tilt means that different parts of the planet receive varying amounts of sunlight throughout the year.

* When a hemisphere is tilted towards the Sun, it experiences summer, with longer days and more direct sunlight. When it's tilted away, it experiences winter, with shorter days and less direct sunlight.

2. Orbit Around the Sun:

* Planets follow elliptical orbits around the Sun, meaning their distance from the Sun varies slightly throughout the year.

* This variation in distance can also contribute to seasonal changes, though it's generally a smaller factor compared to axial tilt.

Important Note: The extent of seasonal changes depends on the degree of axial tilt. Planets with a greater tilt experience more extreme seasonal variations, while those with less tilt have milder seasons or none at all.

For example:

* Earth: Has a 23.5° tilt, resulting in distinct seasons in both hemispheres.

* Mars: Has a 25° tilt, leading to even more extreme seasons compared to Earth.

* Mercury: Has a near-zero tilt, resulting in almost no seasonal variation.

In summary, a combination of axial tilt and orbital path around the Sun determines a planet's seasons. While axial tilt is the primary driver of seasonal change, orbital variations can also play a minor role.