Carl Sagan Explains How the Ancient Greeks, Using Reason & Math, Discovered That the Earth Isn’t Flat Over 2,000 Years Ago

The denial of sci­ence suf­fus­es Amer­i­can soci­ety, and no mat­ter what the data says, some con­ser­v­a­tive forces refuse efforts to cur­tail, or even study, cli­mate change. Astro­physi­cist Katie Mack calls this retrench­ment a form of “data nihilism,” writ­ing in an exas­per­at­ed tweet, “What is sci­ence? How can a thing be known? Is any­thing even real???” Indeed, what can we expect next from what Isaac Asi­mov called the Unit­ed States’ anti-intel­lec­tu­al “cult of igno­rance”? A flat earth lob­by?

Welp… at least a cou­ple celebri­ty fig­ures have come out as flat-earth­ers, per­haps the van­guard of an anti-round earth move­ment. Notably, [Dal­las Mav­er­icks] guard Kyrie Irv­ing made the claim on a pod­cast, insist­ing, Chris Matyszczyk writes, that “we were being lied to about such basic things by the glob­al elites.” Is this a joke? I hope so. Neil DeGrasse Tyson—who host­ed the recent Cos­mos remake to try and dis­pel such sci­en­tif­ic ignorance—replied all the same, not­ing that Irv­ing should “stay away from jobs that require… under­stand­ing of the nat­ur­al world.” The weird affair has played out like a sideshow next to the main­stage polit­i­cal cir­cus, an unset­tling reminder of Carl Sagan’s pre­dic­tion in his last book, The Demon Haunt­ed World, that Amer­i­cans would soon find their “crit­i­cal fac­ul­ties in decline, unable to dis­tin­guish between what feels good and what’s true.”

Sagan devot­ed much of his life to coun­ter­ing anti-sci­ence trends with warmth and enthu­si­asm, park­ing him­self “repeat­ed­ly, arguably com­pul­sive­ly, in front of TV cam­eras,” writes Joel Achen­bach at Smith­son­ian. We most remem­ber him for his orig­i­nal 1980 Cos­mos minis­eries, his most pub­lic role as a “gate­keep­er of sci­en­tif­ic cred­i­bil­i­ty,” as Achen­bach calls him. I think Sagan may have chafed at the descrip­tion. He want­ed to open the gates and let the pub­lic into sci­en­tif­ic inquiry. He char­i­ta­bly lis­tened to unsci­en­tif­ic the­o­ries, and patient­ly took the time to explain their flaws.

In the very first episode of Cos­mos, Sagan addressed the flat-earth­ers, indi­rect­ly, by explain­ing how Eratos­thenes (276–194 BC), a Libyan-Greek schol­ar and chief librar­i­an at the Library of Alexan­dria, dis­cov­ered over 2000 years ago that the earth is a sphere. Giv­en the geo­g­ra­ph­er, math­e­mati­cian, poet, his­to­ri­an, and astronomer’s incred­i­ble list of accomplishments—a sys­tem of lat­i­tude and lon­gi­tude, a map of the world, a sys­tem for find­ing prime numbers—this may not even rank as his high­est achieve­ment.

In the Cos­mos clip above, Sagan explains Eratos­thenes’ sci­en­tif­ic method: he made obser­va­tions of how shad­ows change length giv­en the posi­tion of the sun in the sky. Esti­mat­ing the dis­tance between the cities of Syene and Alexan­dria, he was then able to math­e­mat­i­cal­ly cal­cu­late the cir­cum­fer­ence of the earth, as Cyn­thia Stokes Brown explains at Khan Acad­e­my. Although “sev­er­al sources of error crept into Eratos­thenes’ cal­cu­la­tions and our inter­pre­ta­tion of them,” he nonethe­less suc­ceed­ed almost per­fect­ly. His esti­ma­tion: 250,000 sta­dia, or 25,000 miles. The actu­al cir­cum­fer­ence: 24,860 miles (40.008 kilo­me­ters).

No, of course the Earth isn’t flat. But Sagan’s les­son on how one sci­en­tist from antiq­ui­ty came to know that isn’t an exer­cise in debunk­ing. It’s a jour­ney into the move­ment of the solar sys­tem, into ancient sci­en­tif­ic his­to­ry, and most impor­tant­ly, per­haps, into the sci­en­tif­ic method, which does not rely on hearsay from “glob­al elites” or shad­owy fig­ures, but on the tools of obser­va­tion, infer­ence, rea­son­ing, and math. Pro­fes­sion­al sci­en­tists are not with­out their bias­es and con­flicts of inter­est, but the most fun­da­men­tal intel­lec­tu­al tools they use are avail­able to every­one on Earth.

Note: An ear­li­er ver­sion of this post appeared on our site in 2017. This ver­sion has been light­ly edit­ed and updat­ed.

Relat­ed Con­tent:

Carl Sagan Pre­dicts the Decline of Amer­i­ca: Unable to Know “What’s True,” We Will Slide, “With­out Notic­ing, Back into Super­sti­tion & Dark­ness” (1995)

Hear Carl Sagan Art­ful­ly Refute a Cre­ation­ist on a Talk Radio Show: “The Dar­win­ian Con­cept of Evo­lu­tion is Pro­found­ly Ver­i­fied”

Carl Sagan Presents His “Baloney Detec­tion Kit”: 8 Tools for Skep­ti­cal Think­ing


Josh Jones is a writer and musi­cian based in Durham, NC. Fol­low him at @jdmagness

by | Permalink | Comments (1) |

Sup­port Open Cul­ture

We’re hop­ing to rely on our loy­al read­ers rather than errat­ic ads. To sup­port Open Cul­ture’s edu­ca­tion­al mis­sion, please con­sid­er mak­ing a dona­tion. We accept Pay­Pal, Ven­mo (@openculture), Patre­on and Cryp­to! Please find all options here. We thank you!

Comments (1)
You can skip to the end and leave a response. Pinging is currently not allowed.
  • David Weiss says:

    Carl Sagen was wrong. Eratos­thenes had to assume an “infi­nite” dis­tance sun for the sun rays to come in par­al­lel when in real­i­ty nobody has ever seen sun rays hit the earth par­al­lel. Then on top of that back then they believed in a geo­cen­tric world. How can you have a mas­sive dis­tant sun orbit­ing a tiny spec earth? You can’t. On the flat earth mod­el the sun is small and close just like we observe and when you have a local light over a lev­el plane you get the same shad­ow dif­fer­ences. Take tow bot­tles and place them on the floor a few feet apart and hold a light direct­ly above one of them. That one will have no shad­ow and the oth­er one will have a shad­ow. Accord­ing to the leg­end of Eratos­thenes you can take the mea­sure­ments and that shad­ow and deter­mine the spher­i­cal­ness of the flat floor. Check my YouTube chan­nel for the real info. DITRH

Leave a Reply

Open Culture was founded by Dan Colman.