Flattening Facts for Kids

The flattening, also called ellipticity or oblateness, describes how much a planet or other celestial body is "squashed" at its poles and bulges at its equator. Imagine a perfect ball. Now, imagine pushing down on the top and bottom of that ball. It would get wider around the middle. That's what flattening means!

This shape is very common for objects that spin, like Earth. Our planet isn't a perfect sphere; it's slightly wider around the middle (the equator) than it is from pole to pole.

What is Flattening?
See also

What is Flattening?

Flattening is a way to measure how much an object looks like a slightly squashed ball instead of a perfectly round one. Scientists use the term "oblate spheroid" to describe this shape.

An oblate spheroid is a 3D shape that looks like a sphere that has been flattened at its poles and bulges out at its equator. Think of a slightly squashed orange or a M&M candy.
The poles are the top and bottom points of the spinning object.
The equator is the imaginary line around the middle of the object, halfway between the poles.

Why Do Planets Flatten?

Planets flatten because they are spinning! When a planet spins, it creates an outward push, similar to what you feel when you spin around quickly. This force is called centrifugal force.

The faster a planet spins, the stronger this outward push becomes.
This force is strongest at the equator, where the planet's surface is moving the fastest.
Because of this outward push, the material of the planet tends to move away from the center at the equator, making it bulge.
At the poles, there is very little or no outward push, so the planet stays flatter there.

Think about spinning a ball of soft clay or dough. As it spins faster, the middle part will start to bulge outwards, and the top and bottom will flatten a bit. Planets, especially when they were young and still forming, were often soft or liquid, making it easy for them to take on this flattened shape.

How Do We Measure Flattening?

Scientists measure flattening using a simple formula. They compare the distance from the center to the equator (called the equatorial radius) with the distance from the center to the poles (called the polar radius).

The formula for flattening (f) is: f = (equatorial radius - polar radius) / equatorial radius

Let's look at Earth as an example:

Earth's equatorial radius is about 6,378 kilometers (3,963 miles).
Earth's polar radius is about 6,357 kilometers (3,950 miles).

Using the formula: f = (6,378 km - 6,357 km) / 6,378 km f = 21 km / 6,378 km f ≈ 0.0033

This number, 0.0033, tells us that Earth is only slightly flattened. If you were looking at Earth from space, it would look almost perfectly round.

Earth's Shape: Not a Perfect Ball

Even though Earth looks round, it's actually an oblate spheroid. This means:

The distance around the equator is slightly longer than the distance around a circle passing through the poles.
Mount Everest, the highest point on Earth, is actually a tiny bit closer to the center of the Earth than the peak of Mount Chimborazo in Ecuador. This is because Chimborazo is much closer to the equator, where the Earth bulges out. So, even though Chimborazo is not as high above sea level as Everest, its peak is further from Earth's center.

This slight bulge affects things like:

Gravity: Gravity is slightly weaker at the equator because you are a little further from the Earth's center.
Measurements: When scientists map the Earth or launch satellites, they have to consider this flattened shape for accurate calculations.

Flattening in Other Space Objects

Many other planets and celestial bodies also show flattening, especially those that spin quickly.

Jupiter and Saturn: These gas giants spin very fast and are much larger than Earth. They are noticeably flattened. Saturn, for example, is very oblate; you can even see its flattened shape with a good telescope.
Stars: Some stars spin incredibly fast and can be very flattened, almost like a pancake.
Asteroids: Smaller objects like asteroids usually don't spin fast enough to become perfectly round or significantly flattened. Their shapes are often irregular.

Why is Flattening Important?

Understanding flattening is important for several reasons:

Navigation and Mapping: For accurate maps, GPS systems, and air travel, knowing Earth's exact shape is crucial.
Satellite Orbits: Satellites orbiting Earth are affected by its slightly uneven gravity field, which is caused by the equatorial bulge. Scientists need to account for this to keep satellites in their correct paths.
Planet Formation: Studying the flattening of planets helps scientists learn about how planets formed and how fast they spun in their early stages.

Flattening facts for kids

Contents