Why is Earth tilted

For the uninitiated, yes, our planet is tilted. The Earth is at an angle of approximately 23.43° to its orbital plane. The following figure should help - 

Earth's axial tilt. Courtesy: Wikipedia

So it is natural to wonder why the Earth is tilted in the first place and not perpendicular to its orbital plane.

Well, there is no definite answer for this question but there is a theory.
To understand why, we need to go back in time billions of years, when the solar system was just taking shape. The early solar system was a rough and violent environment with lots of gas, rocks and other junk colliding with each other, knocking each other off their paths and coalescing. Gradually this colliding-and-clumping led to the current state of the solar system with Sun at the center and eight planets around it and millions of smaller junk particles (asteroids) floating around. 

Rarely however, after a planet is formed and starts revolving/rotating, it would encounter a massive collision with something big enough to impact the planet's course (a large asteroid or a planetessimal). Experts theorize that a series of such collisions with massive asteroids is the reason for the tilt of our planet. 

In the early days such collisions were not uncommon. In fact Moon itself was formed by one such collision that ejected lots of debris that eventually got together to form Moon. However, it is very unlikely that a collision of that scale would happen now because there is no known asteroid out there on a collision path and big enough to change the course or angle of Earth. Even if there is one (there are some smaller ones), we would deflect it. So, don't worry!

Does it help?
Like many things that are perfectly tuned for life, Earth's tilt is also perfectly tuned for life as we know it. It is this perfectly calibrated tilt that allows for the seasons and weather conditions that are not extreme but perfectly suited for life. If there was no tilt, like some other planets, Earth would have been too hot for some time and then too cold. 

But hey, an intelligent designer did not tilt the Earth to support life. It just happened and if it did not happen, we wouldn't even be here to question why it did not happen!

Did the simple science for kids in this post make you a little smarter?
If you have any ideas / questions you want to learn about, please leave a note in the comments section. 
Would be glad to know if there are any inaccuracies in the article.


  1. Nice summary. You might also add info about tilt of other planets. They all tilt some amount but there is quite a range.

  2. The rotating Earth is a gyroscope driven by the Circular Inertia of its molten iron outer core

    The molten Iron is concentrated within the tropics as is evidenced by the bulge in the Earth’s surface at the Equator and can be considered as a rotating disc

    As the molten Iron disc rotates the Iron moves cyclically in and out of phase with the Earth’s Linear Inertia

    This causes the molten Iron to slow down when anti-phase and speed up when in-phase with the a corresponding increase and decrease in the density of the molten iron

    The result is that one side of the molten Iron disc is permanently heavier than the other side which causes the disc and the Earth to tilt

    The tilting continues until the Angular Momentum (L=Iω) is constant throughout the molten Iron

    Where the Moment of Inertia is (I) is large the Angular Velocity (ω) is small and where the Moment of Inertia is (I) is small the Angular Velocity (ω) is large

    The condition of constant Angular Momentum is reached when the Earth tilts to an angle of 23.4°

    The Earth’s molten Iron gyroscope is self regulating and maintains the 23.4° Tilt Angle
    From "The Iron Universe" by Joel Savory

    1. This is a bold claim. Is there any math or scientific support for this claim?

  3. this is actually a very helpful article