When we think of looking at the Earth in space we often think of it as a perfect round sphere, but in reality, this is not the case. It all started off thinking that the Earth was flat. That if you sailed to the end of the sea you would fall off the edge of the Earth. After many years of theories, research and calculations we did prove that the Earth is round. However, there are factors that are making the planet change shape very slowly constantly such as: Earth’s rotation, wobbly motion, gravitational and magnetic forces, meaning the earth isn’t completely round.
In scientific words the term is called a geoid, this is what they use to describe the shape of the Earth. A geoid is an irregular-shaped “ball” similar to a scrunched up piece of paper or even similar to the shape of a potato! Due to the uneven distribution of mass throughout the Earth, the geoid’s shape is smooth but irregular. Therefore scientists use an estimated surface size of this ball to calculate depths of earthquakes more accurately. Or to calculate how deep objects are beneath the Earth’s surface. It’s like an imaginary starting point for the sea level that cuts through the land without going up the mountains or down the valleys.
In the words of an oceanographer on the GOCE team this is their description of a geoid. A smooth surface, so much so that if you placed a marble anywhere on it, it would remain where it was rather than rolling in any direction. To be classified as a perfect sphere, an object must be completely round and symmetrical. It needs to be able to be diced down the middle from any direction and create two equal halves. With Earth’s irregular shape caused by all the forces acting on it and it’s deep cracks in the ocean floor, it is anything but symmetrical.
An oblate spheroid
The shape of the world is what we call in fact an oblate spheroid. An oblate spheroid is a sphere that has been squashed, like a basket ball when it bounces on the ground. In terms of Earth, the poles are slightly flatter comparted to where it bulges at the equator. The Earth’s equatorial diameter is about 7,926 miles whereas the polar diameter is about 7,900 miles. The difference is about 26 miles between them which does not sound like a lot at all. This shape is caused by the Earth’s rotation and the centrifugal force it creates.
The shape of the Earth is not only changed due to it’s rotation. But also because of the gravitational pull of the Sun and the Moon. This gravitational pull from the Moon creates tides on the Earth’s surface, this causes the Earth’s crust to bulge at the points closest to and farthest from the Moon. The gravitational pull of the Sun also creates a similar effect, though it is less pronounced.
The oblate shape of the Earth also affects our planet’s gravity. At the equator, the centrifugal force caused by the Earth’s rotation is stronger. This makes the gravity there slightly weaker than it is at the poles. This means that an object weighs slightly less at the equator than it would at the poles.
In conclusion, the Earth is not a perfect sphere, but rather an oblate spheroid/geoid. This is due to the Earth’s rotation, magnetic, centrifugal and gravity forces all altering the shape slowly over time. Next time you do a solar system display use a scrunched up bit of paper for Earth!
Let’s talk about looking the other way for a minute! Looking from Earth up to space, catch a moment of it forever with your very own personalised star map here!