The Earth is not flat

A post on Instagram claims that balloons spotted in the sky above North America last month are evidence that satellites are “fake”. A caption on the post says: “Earth is flat and satellites are fake”.

This is not true. Man-made satellites are real. Amongst other things, they are the basis for the GPS system that is used by mobile phones.

And the Earth is round. Or to be precise, it is roughly spherical. This is one of the most solidly established facts in science.

We often see conspiracy theories like this being shared on social media—including those suggesting that aircraft contrails are part of a secret plot to poison the world or control the weather, the 5G network caused the Covid-19 pandemic or that the World Economic Forum or the World Health Organisation plan to depopulate the world.

None of this is true, but it can harm people’s ability to make informed political choices, or even their health, if they believe it.

Why we know the Earth isn’t flat

There are many ways to prove that the Earth is spherical. Indeed people were able to demonstrate this in several ways more than two thousand years ago.

Aristotle, for instance, observed that the Earth’s shadow on the moon during a lunar eclipse is always circular.

The Greek mathematician Eratosthenes and the Roman-Greek-Egyptian mathematician Ptolemy were able to estimate the circumference of the Earth quite accurately, by measuring the angle of the sun in different places at the same time.

We now know that if the Earth were a flat disc instead of a sphere, gravity would also tend to pull people at the edges inwards towards the centre, not just down towards the surface—with all sorts of strange effects that we do not observe.

Many of our observations in geology, such as plate tectonics, are not explained by a flat Earth.

A spherical Earth is also a fundamental fact of navigation.

And of course we have many photographs of a spherical Earth from space.

Image courtesy of US Government