Why does the horizon look flat?
From the beach, the horizon looks perfectly flat. A rapper has asked where the curve is, NBA stars have said the Earth is flat, and a Spanish football club changed its name to defend the idea. So how do we actually know the shape of the planet we live on?
The claim
Flat Earth supporters say the Earth is not a globe but a flat surface, and that the curve we are told about cannot be seen. In January 2016, the rapper B.o.B posted a photo of two cities about 16 miles apart and asked on Twitter: "where is the curve? please explain this" [1].
Where it came from
The intuition behind the idea is real: close up, the curve of the Earth is hard to see because the planet is so large. Answering B.o.B, astrophysicist Neil deGrasse Tyson calculated that over that distance the curve hides about 150 feet of a city's skyline, while most buildings in midtown Manhattan are much taller than that [1].
Who promotes it
In February 2017, basketball player Kyrie Irving cast doubt on the shape of the Earth on a podcast. In October 2018 he apologised, in particular to science teachers: "I'm sorry. I apologize" [2].
In 2017, Shaquille O'Neal was asked on a podcast whether he was messing with everybody about the flat Earth. "No, the Earth is flat. Would you like to hear my theory?", he answered. "The first part of the theory is, I'm joking, you idiots" [3].
In Spain, former footballer Javi Poves renamed the club he presided, Móstoles Balompié, as Flat Earth FC in 2019. He said the club was born "to unite the voices of millions of flat earth movement followers", and that a club was "the best way to have a constant presence in the media" [4].
Where it spreads today
The doubt reaches beyond a few famous names. In a 2018 YouGov survey of 8,215 American adults, only 66% of 18-to-24-year-olds said they firmly believed the Earth is round [5].
What the evidence says
The Earth was measured long before satellites. Around 240 BC, the Greek scholar Eratosthenes noticed that at noon on the summer solstice the sun shone straight down a well in Syene, while in Alexandria a stick cast a shadow of about 7.2 degrees. From that angle and the distance between the two cities, he estimated the Earth's circumference at about 250,000 stadia, a figure close to the modern value [6].
Today the shape is measured precisely. NASA gives the Earth an equatorial radius of 6,378.137 km and a polar radius of 6,356.752 km: a sphere slightly flattened at the poles [7].
Satellites go further. In 2011, the European Space Agency's GOCE satellite completed a map of the Earth's gravity with unprecedented precision, used to model the geoid, "the shape of an imaginary global ocean dictated by gravity in the absence of tides and currents" [8].
Evidence behind this entry
Distinct sources cited, by tier.
| Tier 1: Systematic reviews and official positions | 2 |
|---|---|
| Tier 2: Studies, rulings and records | 0 |
| Tier 3: Journalism and expert organizations | 6 |
| Tier 4: Claim sources | 0 |
Verdict
The Earth is not flat. Its size was estimated more than two thousand years ago with a stick and a shadow, and space agencies now measure it in detail: a sphere slightly flattened at the poles. The horizon looks flat because the planet is enormous, not because it has no curve.
Sources
Tier 1: Systematic reviews and official positions
- 7. Earth Fact Sheet. NASA Goddard Space Flight Center, 2024-11-15. nssdc.gsfc.nasa.gov
- 8. GOCE delivers on its promise. European Space Agency (ESA), 2011-03-04. esa.int
Tier 3: Journalism and expert organizations
- 1. Flat-earth believer B.o.B. battles Neil DeGrasse Tyson on Twitter. CBS News, 2016-01-26. cbsnews.com
- 2. Kyrie Irving On Flat-Earth Comments: 'I'm Sorry'. CBS Boston (The Associated Press), 2018-10-01. cbsnews.com
- 3. Shaq was apparently trolling everyone when he made his flat-Earth comments. CBS Sports (Matt Moore), 2017-03-23. cbssports.com
- 4. Spanish soccer team renames itself Flat Earth FC to promote fringe theory. Fox News (Ryan Gaydos), 2019-07-01. foxnews.com
- 5. 34% of young adults not sure if Earth is round. FOX 32 Chicago, 2018-05-06. fox32chicago.com
- 6. June, ca. 240 B.C.: Eratosthenes Measures the Earth. APS News, American Physical Society (Alan Chodos), 2006-06-01. aps.org