In ancient times, people believed that the Earth was flat, either in a round or square shape, and even today, some still adhere to the flat Earth theory.
Since ancient Greek astronomers observed the sky and the round Moon, scientists have known that the Earth is spherical.
An image of a tropical storm taken from the International Space Station clearly shows the curved surface of the Earth (Photo: NOAA/Getty Images).
Today, we see many images of the Earth from space, captured by astronauts or sent back by orbiting satellites. But why can’t we see the Earth as round when standing in a park or looking out the window?
The answer lies in the perspective. Humans are very small creatures living on an immense sphere.
Imagine you are a performer in a circus, standing on a ball with a diameter of about 1 meter. When looking down at the ball, you will see it curving in every direction.
Now imagine a bee perched on that ball; because it is much smaller than the ball, it cannot see the entire ball.
The Earth has a diameter of about 12,800 kilometers. Even an adult standing on the ground has a line of sight only about 2 meters above the ground, which means we cannot see the entire spherical shape of the Earth when standing on its surface. Even if you climbed to the summit of Mount Everest at 8,850 meters, you would still not be able to see the Earth as a sphere.
Only at an altitude of 10 kilometers can you see that view, because the length of the horizon we can see depends on our height above the ground.
Standing on the ground without any obstruction, we can see the horizon about 4.8 kilometers away. This distance is not enough to perceive the curvature of the Earth.
To see the entire Earth as a sphere, you must fly at the altitude of satellites or spacecraft.
Some large commercial aircraft can also fly high enough to see the Earth’s surface slightly curving, but it is clearer from the cockpit than from a passenger seat.
In this photo taken from an airplane flying over Colorado, USA, the Earth’s surface appears curved rather than flat (Photo: Paul Comstock/ Flickr, CC BY).
Even from space, you cannot discover an important fact about the shape of the Earth. That is our planet is not perfectly round.
In fact, the Earth is an oblate spheroid, meaning it is slightly flattened at the poles and bulges at the equator.
This is due to the Earth’s rotation creating centrifugal force. This force causes the Earth to bulge slightly at its “waist.” Additionally, the topographical features on the surface, such as mountains and deep ocean trenches, also alter the shape of this sphere due to variations in the Earth’s gravitational field.
Earth science includes a field known as geodesy, which specializes in studying the shape of the Earth and understanding our planet’s position in the universe.
Geodesy provides a wealth of information, from constructing drainage systems and mapping sea-level rise to launching and tracking spacecraft. It is a critical field in contemporary scientific research.
