## Down Direction of a Globe

A globe is a scaled-down model of the spherical Earth. It can be used to explain the down direction on the real Earth, which is toward the center of the globe. Flat-Earthers like to confuse the down direction explained by the model with that of the real Earth. In reality, the down direction we experience is different from that explained by the globe, which is only a model of the actual Earth.

## Ancient Greeks and Spherical Earth

Ancient Greeks have known spherical Earth since at least the 3rd century B.C. According to historian Otto E. Neugebauer, the Greeks discovered Earth is a sphere from the drastic variation in the stars’ positions & motions between Greek settlements of different latitudes.

## Antipodal Flight Route: Jakarta–Bogota

Jakarta & Bogota are a near antipodal pair: the opposite points on Earth’s surface. We can fly from Jakarta in any direction and arrive at Bogota after traveling a similar distance, irrespective of the direction we leave Jakarta.

Any flight between an antipodal pair has a similar duration even though the different flights have different directions. This fact is only consistent with spherical Earth and cannot possibly be explained if Earth is flat.

For example, on a flat Earth, the flight route of Jakarta–Hong Kong–New York–Bogota is almost a straight route between the two locations. Meanwhile, the Jakarta–Sydney–Auckland–Santiago–Bogota route involves a massive detour, and it should take much longer than the aforementioned straight route. However, contrary to what is expected in the flat Earth model, both routes have a similar flight duration.

## Flight Durations

• Jakarta–Istanbul–Bogota: 12h 0m + 13h 45m = 25.75 hours
• Jakarta–Hong Kong–New York–Bogota: 5h 5m + 16h 0m + 5h 42m = 26.783 hours
• Jakarta–Tokyo–Houston–Bogota: 7h 35m + 12h 5m + 4h 55m = 24.583 hours
• Jakarta–Sydney–Auckland–Santiago–Bogota: 6h 55m + 3h 5m + 11h 0m + 6h 14m = 27.23 hours

## Islamic Rituals and Spherical Earth

Many Islamic rituals rely on the observations of astronomical events. Presently, many such observations are supplanted by calculations involving the knowledge that Earth is a sphere. These calculations give the same consistent results as direct observations on all locations on Earth for several centuries already. The fact confirms that Earth is indeed a sphere.

Some Muslims believe in flat Earth and then try to integrate the belief that Earth is flat into their religion. It results in an interesting phenomenon that they perform their religious rituals using the results of spherical Earth calculations but have severe difficulties accepting the fact. It can result in a spectacular cognitive dissonance after being made aware of it.

## Glass of Water

Earth’s gravity causes water’s surface to curve with the same radius as Earth’s. On glass with a diameter of 10 cm, Earth’s gravity causes the water to form a curvature of 0.00000002 cm, outside other factors like surface tension.

Flat-Earthers like to demand that we prove water curvature in a glass of water. In reality, whatever the container, the curvature of the water surface remains the same as Earth’s radius. On a glass of water, it will be too small to observe.

## Bedford Level Experiment Confirmed the Curvature of the Earth

In 1870, Alfred Russell Wallace took a challenge from a flat-Earther and successfully confirmed the existence of Earth’s curvature in the Bedford level experiment.

Wallace did the experiment on the Bedford Canal. Wallace fixed a black band on the Old Bedford Bridge and observed it with a telescope from the Welney Bridge 6 miles away. Right in the middle, he placed a pole with two discs on it. The telescope, the top disc, and the black band are at the same height above the water.

From the telescope, both discs were seen above the black band, proving the existence of Earth’s curvature.

## Flat-Earthers’ Excuse to Dismiss Observation of the Sky

Flat-Earthers like to dismiss evidence of spherical Earth if it is in the form of an observation of the sky. In reality, many of the observed motions of celestial objects can only be explained if Earth is a sphere. These observations are sufficient to prove that Earth is a sphere and rule out a flat Earth.

## Salar de Uyuni and Other Salt Flats

Salt flats are flat expanses of ground covered with salt and other minerals. Salar de Uyuni in Bolivia is the world’s largest salt flat. Salt flats appear visibly flat, but they still follow the curvature of Earth.

Flat-Earthers claim the apparent flatness of Salar de Uyuni and other salt flats “proves” a flat Earth. In reality, while salt flats appear flat, they still follow Earth’s curvature. On a salt flat, the bottom part of a distant object will be obscured by Earth’s curvature, similar to at sea.

## Archimedes and the Surface of any Fluid

In the 3rd century BCE, Archimedes of Syracuse wrote what we now call the Archimedes’ principle in his book “On Floating Bodies” using the spherical Earth model.

Flat-Earthers like to misuse Archimedes’ principle as if it supports their claim that Earth is flat. In particular, they abuse Archimedes’ principle as if it is a competing explanation against gravity. In reality, Archimedes and other Greek scientists at the time already knew Earth is a sphere, and he explicitly mentioned it in his writings.

## Curvature of Water Surface

If Earth is a sphere, why is the surface of water always flat?

Due to Earth’s gravity, water seeks the lowest potential or as close as possible to the center of Earth. It forms a practically spherical surface centered on Earth’s center. The width of the surface in everyday cases is tiny compared to Earth’s radius. Thus, the water surface looks practically flat but not perfectly flat.

## Qibla Direction Proves Earth is a Sphere

Muslims perform their prayers by facing the Qibla —or the direction to the Kaaba in Mecca, Saudi Arabia. The Qibla direction is traditionally determined from the direction to the Sun when the Sun is directly overhead the Kaaba. If the Sun is visible during that time, it will indicate the direction of the Qibla.

If the observation results are drawn on the so-called ‘flat-Earth map,’ the Qibla will not consistently point to the Kaaba. Only calculations using the spherical Earth model will give us consistent results that agree with centuries of observation from various locations on Earth. The Qibla proves Earth is a sphere.

## Oblate Spheroid Shape of the Earth

The Earth is an oblate spheroid. Its diameter is longer across the equator than between the poles. The difference is tiny, only about 0.3%. It is not possible to notice the oblateness from photographs taken from space without careful measurement.

Flat-Earthers claim that in photos taken from space, Earth appears as a perfect sphere, unlike what science tells us, and they use it to discredit science. In reality, it is possible to notice the oblate shape with careful measurement of the images.

Auckland, New Zealand and Madrid, Spain are a near antipodal pair. Both are located at the diametrically opposite points to each other on Earth’s surface. Therefore, we can fly from Auckland in any direction and arrive in Madrid after traveling a roughly similar distance, regardless of the direction taken.

Any flight between an antipodal pair has a similar duration even though the different flights have different directions. This fact is only consistent with spherical Earth and cannot possibly be explained if Earth is flat.

## Antipodal Flight: Shanghai–Buenos Aires

Shanghai, China and Buenos Aires, Argentina are a near antipodal pair. Both are located at the diametrically opposite points to each other on Earth’s surface. Therefore, we can fly from Buenos Aires in any direction and arrive in Shanghai after traveling a roughly similar distance, regardless of the course taken.

Any flight between an antipodal pair has a similar duration even though the different flights have different directions. This fact is only consistent with spherical Earth and cannot possibly be explained if Earth is flat.

## Geoid and Altitude Above Sea Level

The geoid is the shape that the ocean would take under the influence of the gravity and rotation of Earth alone. The geoid is smooth but irregular because Earth’s density and surface are uneven. ‘Height above sea level’ is measured relative to the geoid.

Some flat-Earthers claim that measuring height above sea level is not possible if the Earth is spherical. They are wrong. Height/altitude/elevation is usually measured relative to the geoid, which is approximately a sphere. The geoid is a more accurate model depicting the shape of the Earth, compared to the spherical & ellipsoid model.

## Leveling

Leveling is the process of determining the elevation of a point relative to another point. The curvature of the Earth and atmospheric refraction affect the result of leveling. There are techniques and formulas to correct the effect of Earth’s curvature and atmospheric refraction.

Flat-Earthers assume that construction works like roads, bridges, railways, etc. are built without accounting for Earth’s curvature. They are wrong. The leveling in such works are done in such a way it minimizes the errors due to Earth’s curvature and atmospheric refraction.

## Earth Globe

An Earth globe is a spherical model of Earth with similar purposes to maps, but unlike maps, do not distort the surface that they portray except to scale it down. The Greeks from the 3rd century BC knew Earth is a sphere, and the earliest globe appeared from that period.

Flat-Earthers take the appearance of a globe before NASA existed as a sign of misconduct, like Universal Studios logo from the 20s. They incorrectly claim that it should not be possible to know Earth is a sphere before the first spaceflight. In reality, we knew spherical Earth since 3rd century BC and globes were already commonplace far before the first spaceflight. In fact, the success of spaceflight depends on our understanding of the spherical shape of the Earth.

## The Ball and Water ‘Experiment’

Gravity is the attraction between objects with mass. The higher the mass, the greater is the gravitational attraction. Gravity is not the result of the shapes of the objects.

Flat-Earthers like to perform the ball-and-water ‘experiment.’ They spray water to a ball, then observe the water does not stick to the ball the same way the ocean water curves over the surface of the Earth. They would wrongly conclude that “gravity does not exist.” Gravity does not come from the spherical shape of objects, Continue reading “The Ball and Water ‘Experiment’”

## Geocentrism: Incompatible with the Flat Earth Model

Geocentrism is a superseded description of the universe with Earth at the center. Under geocentrism, celestial bodies all orbited Earth. Geocentrism was the accepted model of the Universe for approximately 18 centuries; before we knew that Earth orbits the Sun —or what we call as heliocentrism.

We often observe flat-Earthers using the arguments for geocentrism as if it supports the flat Earth model. They are wrong. Under geocentrism, the Earth is a sphere, located at the center of the universe. It is not remotely compatible with the flat Earth model, which is an even more archaic understanding of the Universe.

## Air Distance vs Surface Distance

The cruising altitude of a jet airliner is about 33000-42000 ft or 10000-12800 m. It is very tiny compared to the radius of the Earth of 6378 km. Therefore, the distance measured at the cruising altitude does not differ much compared to the surface distance.

Some flat-Earthers claim that if Earth is a sphere, the distance traveled by a jet airliner would have been multiple times the surface distance. They are wrong. The air distance at 33000 ft is only 0.16% farther compared to the surface distance.