How we know Earth is round, not flat: a review of claims and misconceptions about Earth’s shape

The claim that the Earth is flat and stationary has been repeated in countless posts and videos online in recent years. Over 4 years ago, Science Feedback posted a first review of these claims coming from a video published by ‘Flat Earth’ on 17 November 2020. However, these claims have continued over recent years, sometimes with ideas or variations (e.g., dome shaped Earth), but all with the same central idea that ‘Earth isn’t round like we were taught’. 

Claims that the Earth is ‘flat’ and ‘stationary’ directly contradict ample scientific evidence demonstrating that the Earth is round, rotates on its axis, and revolves around the Sun. However, for some people this isn’t enough, as they question the very foundations of science and rely instead on ‘self-conducted experiments’ – often not accounting for other factors that explain what they observe.  

In this review, we will take a two-part approach to addressing the claims: first, we will present the scientific evidence supporting Earth’s round shape, and secondly, we will present common misconceptions and why they rely on faulty reasoning or non-scientific methods. 

Humans have known that the Earth is round for over 2000 years – but how did we discover that?

In 350 B.C.E., Aristotle wrote in On The Heavens, “our observations of the stars make it evident, not only that the earth is circular, but also that it is a circle of no great size.” His conclusion was based on the observation that different constellations and stars can be seen from different locations on Earth, and that the Earth continually casts a round shadow on the Moon throughout a lunar eclipse (Figure 1). 

If the Earth was flat, all stars would be visible regardless of one’s location and the shape of the Earth’s shadow on the Moon would change with the Moon’s position in the sky or as the angle between the Sun and the supposed ‘flat Earth’ changes.

In 240 B.C.E., the Greek mathematician Eratosthenes estimated that the circumference of the Earth was approximately 24,000 – 29,000 miles by measuring the distance between two cities in Egypt and the angle of the Sun’s rays during the summer solstice^[1]. Specifically, he noticed that on the summer solstice, a stick located in the city of Syene cast no shadow, whereas a stick in Alexandria cast a shadow at an angle of about 7.2 degrees. This observed difference in shadow angles is only possible if the Earth’s surface is curved (Figure 2). 

Eratosthenes then hired surveyors to walk from one city to the other, measuring the distance at about 5,000 stadia. Using these measurements, he calculated the circumference of the Earth (Figure 3). Erathosthenes’ estimate was not far off. The Earth is 24,900 miles around the equator and slightly less around the poles, which is why the National Oceanic and Atmospheric Administration (NOAA) refers to its shape as an irregularly shaped ellipsoid (i.e., spherical, but not a ‘perfect’ sphere). 

The Earth, as well as the other planets in our solar system, are spherical because gravity pulls toward the center of an object. However, because the Earth spins on its axis, it is not perfectly spherical. This is because the force of rotating causes the planet to bulge slightly at its equator relative to the North and South poles.

Since then, the spherical shape of the Earth has been confirmed through images from satellites and spacecraft. For instance, astronauts on the Apollo 17 mission to the Moon captured the classic image of the Earth, known as the (original) ‘The Blue Marble’, when they were about 28,000 miles from the surface (Figure 4). 

Some ‘flat Earth’ proponents have suggested there are no real photos of Earth from space and that these photos are ‘fake’ or ‘CGI’. Given the relatively close proximity of satellites to Earth, it is true that a number of more recent photos are composites – combinations of several photos into one. This is necessary because the satellites taking these images are not far enough from Earth to capture the entire planet in one shot. However, the National Aeronautics and Space Administration (NASA) does not hide the fact that certain photos are composites – in fact, they openly explain this on their website.

The photo in Figure 4, however, was captured as a single photo (see film and camera details here), made possible by the great distance (~28,000 miles) that astronauts had traveled away from Earth on their way to the moon. 

In 1851, Léon Foucault found a creative way to demonstrate that the Earth spins on its axis, providing the first empirical evidence of this phenomenon. He hung a pendulum from the ceiling of the Paris Observatory and set it in an oscillatory motion, then watched how the angles of the lines formed by the swinging pendulum changed over the course of a day^[2]. 

On a non-rotating surface, a pendulum released in a specific direction (without forces from other directions) would swing along a consistent plane without deviation, tracing a single line relative to the ground. However, on a rotating planet, the ground beneath the pendulum and the point it is fixed to are also rotating. Because of this, the swing plane of a Foucault pendulum appears to move relative to the rotating ground – tracing out different lines throughout the course of a day. The time it takes for this plane to make one full rotation depends on its latitude on Earth; notably, if located at the equator, it will not appear to rotate at all. 

However, a (properly) released Foucault pendulum traces out different angles over the course of a day – a simple experiment that Foucault used to demonstrate that Earth is rotating. (See a simple visualization of this effect in the link here). This rotation – along with the tilt of the Earth on its axis and its revolution around the Sun – explains why we experience day and night as well as seasons (Figure 5).

Another observation that can only be explained by a round, rotating planet is the influence of the Coriolis Effect on weather patterns (Figure 6). The Coriolis Effect* describes a phenomenon in which moving objects’ paths deflect or curve when moving within a rotating ‘reference frame’ – like a rotating planet. On Earth, this causes winds to appear to curve rather than follow a straight path – a consequence of air moving across a rotating planet.

Latitudes above and below Earth’s equator have a smaller circumference than the equator. But the points along all latitudes on Earth must rotate once in 24 hours – the length of a day. However, because areas near the equator (i.e., largest circumference) have to travel along a bigger ‘circle’ in that time, they have to move faster. Think of this like running on a track – to complete one lap, those on the outside have to run faster than those on the inside because the outside ‘ring’ is larger. So on Earth, the latitude-dependent velocity causes winds to appear to deflect towards the poles – to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. (Similarly, tropical cyclones spin counterclockwise in the north and clockwise in the south.) This hemispheric difference would be impossible on a flat Earth.

*Note: The Coriolis Effect can be tricky to visualize. For a visual aid, watch the video linked here.

As demonstrated above, and contrary to the claim that the Earth is stationary – one of the underlying claims of ‘flat Earth theory’ – it is well-established through multiple lines of evidence that the Earth rotates on its axis and revolves around the Sun. But what about the so-called ‘experiments and observations’ that the ‘flat Earth’ believers claim to prove otherwise? Let’s investigate these below. 

Common misconceptions and problems with ‘flat Earth’ experiments and ideas

As we explained, there are numerous variations of ‘flat Earth’ claims – more than we can reasonably review here. As such, we will investigate a few of the main claims below and explain the flaws in their experiments and reasoning. 

Misconception 1:

‘If the Earth is a spinning sphere, planes and helicopters should just hover while the Earth spins below it‘

Verdict: Incorrect. 

Quick takeaway: The Earth is rapidly spinning, and because of gravity and the law of inertia, so too is the atmosphere and everything on Earth’s surface. This includes planes that take off and the atmosphere (i.e., air) they fly into. So when a plane takes off and starts moving, it is moving in an atmosphere that is rotating/spinning at the practically same speed and direction (eastward) as Earth and the plane are. If the solid Earth was the only thing spinning, you could not jump without the ground below you rotating away, and you would also feel blistering winds that match the rapid speed of Earth’s rotation, as the Earth drags you through the air at that speed. 

Details: This claim is rooted in a misunderstanding of how planets (e.g., Earth) influence nearby matter/objects. More specifically, the misconception here is that ‘things only spin with the Earth while they are touching it’, or that ‘only Earth’s solid body is rotating’. However, these ideas are incorrect and ignore the physical laws of gravity and inertia. 

Things with mass on or near Earth – relatively speaking – are attracted by Earth’s gravitational field. Earth’s atmosphere has mass and is therefore attracted and bound close to Earth by gravity. This is why Earth can have an atmosphere at all and why its air hasn’t escaped into the vacuum of space. But why does the atmosphere spin along at (roughly) the same rotational speed as the ‘solid’ Earth does, and how do we know that’s the case?

It’s easiest to start with what we would observe if Earth’s atmosphere did not spin with the rest of Earth. Let’s start by imagining what your hand would feel when sticking it out of a car window while driving at high speeds. Those who have done this know that you would feel a continuous stream of air rushing over your hand. Even if the air isn’t moving with respect to the ground, you feel air moving because you and the car are passing into the (let’s say stationary, in this case) air at a certain speed – 60 miles per hour (mph), for example. Therefore, the air feels as if it is moving at 60 mph because your hand is moving through it at that speed. 

Similarly, if only the Earth and things on its surface – like you – were spinning, but not the atmosphere, you would feel wind rushing past you at a blistering speed of 1,040 mph (1,674 kilometers per hour) – the speed of Earth’s rotation at the equator (varying with latitude, as explained earlier). As you know, this is not the case. This is because Earth’s atmosphere is, roughly speaking, spinning along with you and the Earth. This is a result of the physical laws described above, along with Earth’s surface ‘dragging’ the atmosphere via friction and the atmosphere’s viscosity. So gravity explains why things are bound close to Earth, but why does matter in or on Earth spin along with the planet?

The Earth began forming 4.5 billion years ago after clouds of dust and gas collapsed under gravity and began compacting and spinning. Since then, Earth – and all matter contained in/on it – has been spinning as a system. Newton’s first law of motion – also known as the law of inertia – dictates that an object in motion stays in motion unless acted upon by an outside force. 

This means that all matter that is bound to Earth – or near Earth’s surface, in the case of the atmosphere – and is rotating with Earth, will continue to do so unless an outside force stops it. For this reason, when a plane takes off, or you jump in the air, the ground does not spin away. In essence, you, the plane, the ground, and the atmosphere are spinning with the rest of Earth as a system. 

Misconception 2:

‘Antarctica doesn’t exist and is just an icewall‘

Verdict: Incorrect. 

Key takeaway: Several independent sources and lines of evidence show that Antarctica does exist and is in fact a continent, not an ‘ice wall’. The fact that it is not an ‘ice wall’ is proven by several different lines of evidence:

• Satellite imagery of Antarctica showing that it is continental landmass –  not a wall (linked here and here; see Figure 7);
• Photos taken in Antarctica showing mountains and other rocky terrain (i.e., not just ice) (linked here);
• Ship records and Antarctic expeditions (linked here);
• Continental movement via plate tectonics (as we will explain below). 

Details: 

In recent years, social media posts have gone viral after claiming that Antarctica is an ‘ice wall’ rather than a continent. The ‘ice wall’ mentioned in these claims is part of ‘flat Earth theory’ – together claims are part of a conspiracy theory suggesting that our model of Earth is ‘not what we were taught’. Though these posts claim that there is a supposed ‘ice wall’ surrounding our oceans, there is no evidence that this is the case. 

Several lines of evidence shows that Antarctica is a continent, not an ‘ice wall’ as claimed in social media posts in recent years. One of the strongest pieces of evidence is satellite imagery of Antarctica which shows the landmass is an isolated continent surrounded by water (Figure 7). 

There are well over a century of records of ship voyages to the continent and Antarctic expeditions where scientists and explorers have traversed the continent on foot (linked here). And voyages continue to this day. In the 2022-2023 season, Antarctica saw more than 100,000 tourists. 

But it’s not just tourists who visit the continent. Scientists from around the world visit and work at bases in Antarctica to conduct scientific studies (e.g., collecting ice cores to study past climates). During their stay, they have taken photos of certain geographic features in Antarctica – such as mountains and other rocky terrain – sticking up from the ice. This is evidence that Antarctica is an ice-covered landmass underlain by normal continental features (e.g., mountains) – not just a ‘wall of ice’.  

Scientists have also studied how the continent of Antarctica formed and moved over time. Evidence shows that Antarctica began slowly moving to its current position roughly 182 million years ago^[3,4]. At that time it was part of a larger supercontinent called Gondwana (Figure 8) – which also included land that we now call South America, Africa, Madagascar, India, Western Australia, and Arabia^[4]. These studies show that Antarctica is not just floating ice, but a continent that has been studied like the others – albeit to a lesser extent given its inhospitable environment. 

Misconception 3:

‘There is no observable curvature to Earth’

Verdict: Factually inaccurate. 

Key takeaway: 

There is ample photographic and video evidence captured from satellites and spacecraft showing the curvature of the Earth. However, when taken from the correct height/distance from Earth’s surface – and with an unobstructed view – Earth’s curvature is clearly evident (see NASA footage here). 

Read more about the history of photographic proof of Earth’s curvature in the link here.

Details:

A number of social media posts have been shared online in the past attempting to ‘disprove’ that Earth’s surface is curved. However, none have provided credible evidence that refutes Earth’s curvature that we’ve observed in ample photographic and video evidence captured from satellites and spacecraft. Instead, these posts often show photographs taken on or near Earth’s surface, often introducing well-known visual phenomena and distortions (e.g., mirages). 

For example, one post shows a photo of the Chicago skyline peeking out from a body of water, with a caption that reads ‘there is no globe’. This photo from 2015 was reportedly captured at a distance of 60 miles away, which some claim is evidence of a ‘flat Earth’ because the city should be beneath the horizon at that distance. However, as explained in previous fact checks (here and here), this observation is compatible with a spherical Earth and is caused by a phenomenon called atmospheric refraction. 

It’s a misconception to think that light always travels in a straight line from an object to our eyes, telling us exactly where it is. In reality, light’s path can bend depending on the medium it is passing through. For example, if you look at a straw in a glass of water, you will notice that – although you know the straw to be straight – it appears to bend in the water. This is caused by a ‘bending’ of light’s path of travel – otherwise known as refraction. This also occurs in Earth’s atmosphere, and is known as atmospheric refraction – which explains the tendency of light to bend its path as it encounters different air densities.

In this specific case, atmospheric refraction caused a superior mirage – a mirage in which objects appear higher than they are in reality (Figure 9). This allows objects (buildings, boats, etc.) that are beyond the horizon to appear above it. This is why using images taken on Earth can be misleading without understanding the context and settings in which it was taken (e.g., height at which the photo was taken, height of the objects, atmospheric conditions that day etc.). 

However, this problem is eliminated when looking at the planet from space, which shows Earth’s shape relative to the void of space around it (Figures 10 and 11). Using this evidence, along with numerous other experiments noted earlier, it is abundantly clear that Earth is curved and with an overall spherical shape. 

Misconception 4:

‘Compasses and gyroscopes prove the Earth is not a globe’

Verdict: Incorrect.

Key takeaway: Compasses and gyroscopes do not ‘disprove’ that Earth is globe; in fact, their behaviors are compatible with scientists’ model (and direct observations) of Earth as a spherical, rotating planet. 

Details: In the past, ‘flat Earth’ proponents have claimed that compasses and gyroscopes prove the Earth is not a globe, but these claims do not provide any scientific evidence to support this claim or explain how this might occur. Compasses contain small, lightweight magnets and are used to detect Earth’s magnetic field, which results from movements of liquid iron and nickel in the Earth’s outer core that carry an electrical current. As a result, the Earth has two distinct poles (north and south). The needle of a compass points to the magnetic north pole, which slightly differs from the geographic north pole. Depending on one’s location, it is possible to use a compass to map Earth’s magnetic field (Figure 12). Given that having a north and south magnetic pole fit within the model of a spherical Earth – because having an outer liquid core is part of that model – compasses and their observed behavior are also compatible with a spherical Earth.

A gyroscope is a device that contains a spinning wheel that is mounted in a way that allows the axis to freely assume any orientation. Gyroscopes are used to measure or maintain orientation and angular velocity, and can be found in navigation systems of airplanes, ships, and space stations. Scientific studies have used a newer type of gyroscope – called a chip-based laser gyroscope – to detect the Earth’s rotation with better precision^[5] by using something called the Sagnac effect. In an article summarizing this research, CalTech explained how these gyroscopes were used to measure Earth’s rotation:

“Two light waves traveling in opposite directions around a ring-like path will have equal propagation times. However, when the path rotates, the time to reach a specific point on the rotating path will be different for each wave. This difference provides a measure of the rate of rotation and can be determined very precisely by measuring the interference between the two light waves.”

References:

1. (1943) Eratosthenes and the Circumference of the Earth. Nature.
2. Sommeria (2017) Foucault and the rotation of the Earth. Comptes Rendus Physique.
3. Moulin et al. (2011) An attempt to constrain the age, duration, and eruptive history of the Karoo flood basalt: Naude’s Nek section (South Africa). Journal of Geophysical Research: Solid Earth.
4. Svensen (2018) Gondwana Large Igneous Provinces: plate reconstructions, volcanic basins and sill volumes. Geological Society, London, Special Publications.
5. Lai et al. (2020) Earth rotation measured by a chip-scale ring laser gyroscope. Nature Photonics.