Escaping the human scale

Originally published 12 October 1987

When I was a child I owned a pic­ture book that told the sto­ry of Christo­pher Colum­bus. Sev­er­al of the illus­tra­tions are still clear in my mem­o­ry. One showed Span­ish car­avels, with pen­nants fly­ing, sail­ing off the edge of a flat Earth into the mouth of a wait­ing mon­ster. This sup­pos­ed­ly illus­trat­ed the pre­vail­ing view of the shape of the Earth at the time of Columbus.

Anoth­er pic­ture showed Colum­bus stand­ing before Queen Isabel­la with an apple in his hand. “I believe the Earth is round like this apple,” he tells her, “give me ships and crews to sail them and I will prove it.”

And so it was that one more kid learned the myth that Colum­bus was the first to imag­ine that the Earth was round.

Colum­bus did not have to con­vince any­one of that the Earth was a sphere. All geo­g­ra­phers since the time of the Greeks knew that the Earth was shaped like a ball. Nor was Colum­bus the first to imag­ine that he could reach Asia by sail­ing west­ward across the Atlantic. Aris­to­tle report­ed­ly said it could be done. More than a thou­sand years before Colum­bus the Greek geo­g­ra­ph­er Stra­bo record­ed that Greek and Roman sailors had attempt­ed the crossing.

None of which detracts from Colum­bus’ achieve­ment. To have launched out onto the unchart­ed west­ern sea in three tiny ships required spec­tac­u­lar courage, no less than that required by the first Amer­i­can astro­nauts who embarked for the Moon. Colum­bus returned from his voy­age con­vinced he had reached the Indies. The astro­nauts returned from their jour­ney to the moon with pho­tographs of the blue-white plan­et Earth sus­pend­ed in the black of space, more per­fect­ly round than any apple.

Even with those pho­tographs before us, cer­tain erro­neous views per­sist regard­ing the shape of the Earth. One com­mon mis­con­cep­tion is that the Earth is “pear-shaped” or “squished flat” at the poles. School books fre­quent­ly show a draw­ing of a gross­ly ellip­ti­cal Earth, and that exag­ger­at­ed image has a curi­ous way of stick­ing in the mind.

Planet is an ellipsoid

The Earth­’s shape is indeed an ellip­soid (or very close to it), a shape impart­ed to the plan­et by its rota­tion. But the diam­e­ter of the Earth at the poles is less than the diam­e­ter at the equa­tor by only 29 miles out of near­ly 8000, so the plan­et is “out-of-round” by less than one-half of 1 percent.

No astro­naut’s eye would be sharp enough to notice this depar­ture from spheric­i­ty. The “pear shape” of the Earth cer­tain­ly isn’t notice­able on pho­tographs. If a bowl­ing ball were as lop­sided as the plan­et Earth you could still roll a fair game of strikes.

Text­book illus­tra­tions also exag­ger­ate the rough­ness of the Earth­’s sur­face. It is dif­fi­cult to grasp just how smooth the plan­et actu­al­ly is. We talk of the “mighty” Andes and “tow­er­ing” Himalayas as if they con­sti­tut­ed con­sid­er­able bumps on the Earth­’s sur­face. But the sur­face of the Earth is rough only on a human scale. Put a scaled-down ver­sion of Mt. Ever­est on a bowl­ing ball and it would be less than a hun­dredth of an inch high, or about the thick­ness of a piece of paper. If the sur­face of the bowl­ing ball were mod­eled exact­ly to rep­re­sent the sur­face of the Earth, from high­est moun­tain peaks to deep­est ocean trench­es, your eye would not detect nor your hands feel the depar­ture from smooth­ness. And you could still roll a win­ning game.

The blue-white plan­et that we see in space pho­tographs takes its col­or from sea and cloud. But even the oceans and the atmos­phere are of gauze-like dimen­sion on the scale of the Earth. On the bowl­ing-ball, the atmos­phere would be a wrap of air about as thick as three or four sheets of paper. Dip the ball in a tub of water and shake it off and the film of damp that would remain is suf­fi­cient­ly deep to be the oceans. A cos­mic giant who picked up the Earth in his hands would hard­ly be aware that what he was hold­ing was any­thing oth­er than a smooth, round rock.

Forget the human scale

And, of course, that’s exact­ly what it is. Oceans, atmos­phere, moun­tains, and val­leys are only con­sid­er­able by com­par­i­son to our­selves. To imag­ine the plan­et Earth as it real­ly is we must first escape the lim­i­ta­tions of human scale. Eratos­thenes of Alexan­dria in the 3rd cen­tu­ry B.C. suc­cess­ful­ly mea­sured the Earth­’s size, by math­e­mat­i­cal rea­son­ing and obser­va­tions of shad­ows cast by the sun. But first he had to imag­ine a smooth, spher­i­cal Earth on which the high­est moun­tains and deep­est val­leys have shrunk to insignif­i­cance. In doing so, Eratos­thenes and his con­tem­po­raries per­fect­ed a new way of think­ing — today we call it science.

And this was Colum­bus’ real achieve­ment. He was not the first to con­ceive that the Earth was round, nor was he first to assert that Asia could be reached by sail­ing west­ward. But he did suc­cess­ful­ly free him­self from the lim­i­ta­tions of human scale.

It is one thing to know some­thing as a bit of school­book infor­ma­tion; it is some­thing else to ful­ly com­pre­hend the real­i­ty of a thing in the mind’s eye. Colum­bus’ con­cept of a spher­i­cal Earth was suf­fi­cient­ly clear to sus­tain him on one of the great voy­ages of dis­cov­ery. In this he was more than a nav­i­ga­tor, more than Admi­ral of the Ocean Sea. He was a man of imag­i­na­tion and science.