Is Earth like an upright egg, or a squashed spheroid? It would take an epic 18th century expedition to finally find out.
Earth is round. The vast majority of people know and accept this, and there are indeed ways to prove that Earth is round, not flat.
But Earth isn’t completely round: the speed at which our planet spins makes it more of a squashed shape, with the north and south poles slightly flattened.
You can find out more about this in our video demo below.
Discovering the true shape of Earth
The ancient Greeks believed that circles and spheres were the perfect shapes, a belief which carried over into Old World science.
This idea wasn’t challenged until the Enlightenment era, leading to two new theories about our planet’s shape.
French philosopher René Descartes’s theories about vortices in the ether suggested Earth was shaped like an upright egg, stretched towards the poles.
Meanwhile, Isaac Newton’s theory of gravity suggested Earth’s spin would make the equator bulge out, while flattening the poles.
Knowing which was true would greatly increase the precision of naval navigation, so the French and Spanish governments sponsored two expeditions to solve the issue.
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One would head to Lapland near the Arctic circle, the other to the equator, to measure the length of one degree of latitude.
If Lapland was longer, Decartes was correct; if it was the equator, then it was Newton.
In 1735, an expedition set sail for the Andes in modern-day Equador.
Bad planning, extreme weather, volcanic eruptions and a leader who spent much of the team’s money buying diamonds for his mistress meant it was a decade before any crew member came home.
By then, the Lapland expedition had long since returned, compared their own measurements to those taken in Paris, and proved that Newton’s idea was correct.
This article originally appeared in the May 2023 issue of BBC Sky at Night Magazine.