Why does our environment seem flat when the Earth is round? 🌍

By Kelly R. MacGregor - Professor of Geology, Macalester College

Since the ancient Greeks made observations of the Moon and the sky, scientists have known that the Earth is a sphere.

We've all seen magnificent images of Earth from space, some photographed by astronauts and others collected by orbiting satellites. So why doesn't our planet seem round when we stand in a park or look out the window?


The answer lies in perspective. Humans are tiny creatures living on a very large sphere.

Imagine you are a circus acrobat standing on a ball about 1 meter (3.3 feet) wide. From the top of the ball, you would see it slope away from your feet in every direction.

Now imagine a small fly on this circus ball. Its point of view would probably be just a millimeter or less (about 0.04 inches) above the surface. Because the fly is much smaller than the ball and its viewpoint is so close to the surface, it cannot see the entire ball.

The Earth is about 12.8 million meters (roughly 8,000 miles) across, and even the view of a tall adult peaks only around 2 meters (6.6 feet) above its surface. It's impossible for our eyes to grasp the size of the spherical Earth when we are standing on it. You couldn't even visualize the Earth as a sphere by climbing to the top of Mount Everest, which rises 8,850 meters (29,035 feet) above sea level.

The only way to see the Earth's curve is by flying more than 10 kilometers (6.2 miles) above its surface. This viewpoint makes it clear that the length of the horizon we see depends on how high we are above the Earth's surface.

Standing on the ground, with no obstructions in our view, our eyes can see about 4.8 kilometers (roughly 3 miles) to the horizon. That isn't far enough for the horizon line to show its curve. Like a fly on a circus ball, we cannot see far enough across where the Earth meets the sky.

To see the entire planetary sphere, you'd need to travel with an astronaut or onboard a satellite. From such a distance, you'd get a full view of the Earth.

Large airplanes can also fly high enough to give a glimpse of Earth's curvature, although pilots typically have a much better view from the cockpit than passengers do from the side windows.

Not quite a sphere

Even from space, you wouldn't be able to spot something important about Earth's shape: it's not perfectly round. It's actually a slightly flattened spheroid or ellipsoid. This means it is a bit wider than it is tall at the equator, like a sphere that has been slightly squished.

This phenomenon results from Earth's rotation, which creates centrifugal force. This force causes a slight bulge around the planet's "waist."

Topographical features on the Earth's surface, such as mountains and ocean trenches, also slightly distort its shape. These features cause small variations in the strength of the Earth's gravitational field.