Hardik Medhi

Every child knows about the various seasons we experience throughout a year.

But why are there different seasons? Why do they change throughout the year? Why is the intensity of each season different in different regions on Earth?

There’s a common notion among the general public that the reason behind the variety of seasons is due to the Earth’s orbit of the Sun — when we are closer, we have summer, and when we are farther away, we have winter.

That notion is, in fact, not entirely true. While the Earth’s orbit does play a role, it doesn’t have a prominent influence. Here’s why. In geometry, there’s a number called eccentricity (denoted by e). It runs from 0 to 1. If a closed shape has an eccentricity of 0, it means it’s a circle. On the other hand, an eccentricity of 1 implies that it’s a highly elongated ellipse.

The eccentricity of Earth’s orbit is 0.0167. That’s almost a circle. This means that there is a minute difference in distance between the Sun and the Earth when we are the farthest away (aphelion) and when we are the closest (perihelion).

This is why the orbit of the Earth does not have a major influence on our seasons.

So, what’s the reason?

The answer lies in Earth’s tilt.

Source: Getty Images

Take a look at the beautiful illustration above.

With respect to the plane of the Earth’s orbit, the planet’s rotation axis is tilted by 23.5 degrees. Because of this, the incoming sunlight is unevenly distributed across the surface. When the Northern Hemisphere is tilted towards the Sun, it experiences Summer, while the Southern Hemisphere has winter. The opposite happens when the Southern Hemisphere is tilted towards the Sun.

This tilt was likely caused by a collision with a large body billions of years ago, when the Earth was still in its early stages. Over time, this tilt of 23.5 degrees played an important role in various biochemical and geological processes that ultimately gave rise to the diverse life that occupies this planet.

Hardik Medhi
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