Proving the Earth is a sphere
IN RECENT MONTHS
news reports have suggested a resurgence in the theory the Earth is actually flat. Some people undoubtedly make the claim as a joke, but apparently others are serious about this belief.
The Earth isn’t flat, of course, but how can we prove that? There are several ways. Here are a few of our favourites.
THE ANCIENT GREEK METHOD
A scholar called Eratosthenes worked out the Earth was a sphere way back in 240 BCE. He did it by whacking a stick in the ground in the Egyptian city of Syene at midday and measuring the angle between it and its shadow. He repeated the experiment in the nearby city of Alexandria and noted the angle was different by seven degrees. Extrapolating from this, he reasoned the Earth had to be round – the angle would have been identical on a flat plain – and that its circumference was 44,100 km. He was out by about 10% – pretty good for a bloke equipped with just two sticks and 10 fingers.
THE HORIZON METHOD
Watch a ship sail away from you. Eventually it will disappear over the horizon. If the Earth was flat, it wouldn’t do that. It would just appear to grow smaller, and with a powerful enough telescope you could track it all the way to Africa.
THE CIRCUMNAVIGATION METHOD
If the Earth was flat, circumnavigation would be impossible. The first person to successfully sail a ship right around the Earth was a Spanish sea captain called Juan Sebastian Elcano, who took three years to do it and arrived back in his home port in 1522. He was originally commissioned by Ferdinand Magellan, who wanted to have the honour of proving the world could be circumnavigated. The boss, however, got himself killed in the Philippines – leaving Elcano and his crew to complete the mission. Since then the world has been circumnavigated millions of times. Passenger and cargo planes to do it every day. In all these millions of journeys over hundreds of years, no one has ever fallen off the edge of the world and gone hurtling into the abyss of deep space.
THE TELEPHONE METHOD
If the world was flat and the Sun just spun around in a circle above it, light would hit the entire surface all at once. Time, therefore, would be the same everywhere, but it’s not. If it’s 5pm in Australia, ring a flat-earther in California and wake him up. It will be midnight the day before in Los Angeles. Time differences can only happen on a rotating sphere.
THE PHOTOGRAPHIC METHOD
Since space travel became a reality in the 1960s, astronauts and satellites have taken vast numbers of photographs of the Earth. All of them show a spherical object floating in space – sometimes with another spherical object, the moon, floating nearby. If all these photographs had been taken from exactly the same spot, it could be argued (as flat-earthers sometimes do) that all they show is a two-dimensional disc. But they haven’t been. They have been taken from multiple angles at multiple distances on multiple occasions. You just can’t fake all this evidence. Besides, if the Earth was flat, cats would have pushed everything off it by now.