Variability of Atmospheric Refraction

In most situations, atmospheric refraction bends light downwards and causes objects to appear higher than they actually are. The strength of atmospheric refraction is not constant. It depends on weather condition and varies on the different seasons, different days, and even different times of the day.

Because of the variability of atmospheric refraction, a distant object that is usually obstructed by Earth’s curvature can sometimes be visible. Some flat-Earthers would cherry-pick moments when the object is visible. They would show such specific moments to everyone and use them to “disprove” Earth’s curvature; happily ignoring the cases where Earth’s curvature partly or entirely obstructs the object.

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White Alice and the Troposcatter Propagation

Troposcatter is a signal propagation method using the scattering phenomenon in the upper troposphere. As the signal pass through the upper troposphere, some of the energy is scattered back toward Earth, allowing the receiver station at the correct location to pick up the signal.

White Alice is a decommissioned troposcatter network in North America. Some flat-Earthers invented the “explanation” that the various satellite-based services we enjoy today are using White Alice. They are wrong. White Alice and other troposcatter networks cannot possibly replace all the services provided by satellites.

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Range Estimation Using the Distance to the Horizon

Sailors sometimes need to estimate the range of a distant contact. Without radars, the only readily available reference point for estimating ranges is the horizon.

By knowing the height of the observer from the waterline, it is possible to calculate the distance to the horizon, and thus, it is possible to determine the distance to a remote contact, relative to the horizon. It is possible to do this only because the Earth is spherical.

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Level, Higher and Lower

A higher position is farther up, away from the center of the Earth, relative to sea level. Conversely, a lower position is closer toward Earth’s center, relative to sea level. Two positions are level if they are at the same height from sea level.

Some flat-Earthers are unable to understand this. To them, ‘level’ means straight. They are wrong. In Earth sciences, height is measured from a plane of reference, usually the sea level.

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Ships Disappearing Over the Horizon and the Various “Explanations” Invented by Flat-Earthers

Due to Earth’s curvature, ships traveling over an ocean disappear from the bottom up. This fact is one of the first evidence to confirm the Earth is a sphere, and one of the first facts of which flat-Earthers had to invent various “explanations” for.

Some of the popular “explanations” are: refraction, perspective, zooming reveal distant ships and visibility limitations. None can explain away the fact.

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Suez Canal

The Suez Canal is a waterway connecting the Mediterranean Sea to the Red Sea. The level of water on both seas is practically the same, and the Suez Canal contains no locks system.

Flat-Earthers are claiming that the Suez Canal was constructed without accounting for curvature. They said if the Earth were spherical, then the middle of the canal should have been 1666 ft deep. This is merely a misconception. The surface of the water is equipotential. It has roughly the same distance to the Earth’s center of gravity. It is not necessary to dig 1666 ft in the middle of the Suez Canal. The engineers only need to ensure the base of the canal is below sea level for sea water to flow.

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Football Field and ‘Flat-Earth Convergence Experiments’

A properly designed football field does not lie perfectly flat. Its middle portion is slightly raised to promote runoff of excess water. Without it, the field can become muddy & uncomfortable.

Some flat-Earthers conducted the perspective convergence ‘experiment’. They put a camera on the surface of a football field, and record a person walking away across the field. The person started to disappear from his feet first. Because they felt the football field is flat, they took the wrong conclusion that the person disappeared due to ‘perspective’. They were wrong. The field is, in fact, not perfectly flat. If it is perfectly flat, the person would appear fully at the end of the field.

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Earth’s Curvature Calculation

The amount of obstruction of a distant object that is caused by Earth’s curvature depends on:

  1. The distance of the object.
  2. The height of the observer.
  3. The height of the object.
  4. The magnitude of atmospheric refraction.

Flat-Earthers like to use the visibility of a distant object to prove Earth’s curvature does not exist. Very often, they failed to account for observer’s height and atmospheric refraction, or make other mistakes, like unit conversions errors, distance calculation errors, etc. Once all are considered for, and mistakes are fixed, everything will be consistent with spherical Earth.

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Infrared Vision

When we are unable to see a distant object, then it is due to one of these reasons:

  • Our eyes lack the sufficient angular resolution to recognize the object.
  • Atmospheric condition limits visibility.
  • The object is far enough and obscured by Earth’s curvature.

Some flat-Earthers like to show that a previously unseen distant object can be brought into view using infrared vision. They would take that as ‘evidence’ of the non-existence of Earth’s curvature. They are wrong. Infrared vision can reveal hidden objects caused by visibility limitations, but not ones obscured by Earth’s curvature.

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Sunset, Camera Zooming, and Autoexposure

There are videos showing the sun to appear to set, but after the camera is zoomed in, the sun is still above the horizon. The reason is that the camera’s autoexposure system is constantly adjusting the exposure, and in such scenes, there’s a difference in overall brightness before and after zooming in.

Flat-Earthers are taking such videos as ‘evidence’ of a receding sun. They are wrong. This is merely a matter of photography. In reality, the sun is not receding, and it has the same angular size throughout the day.

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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 are visibly very flat, but like every other geology features, they all follow the curvature of the Earth.

Flat-Earthers take the flatness of Salar de Uyuni and other salt flats as ‘evidence’ of a flat Earth. They are wrong. While most salt flats appear flat, they still gradually curve and follow the curvature of the Earth.

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The Curvature Fitting Game

The amount of curvature that appears in a photograph of a sphere depends on 1. The radius of the sphere, 2. Camera distance from the sphere, 3. Field of view of the camera, and 4. The distortion characteristic of the camera being used.

The ‘curvature fitting game’ has been flat-Earthers’ favorite pastime. They would try to fit a photograph of Earth’s curvature with another. If they find the result is not proportionally correct, they will make fun of it. They are wrong. Two different photos of a sphere can be taken differently and would show a different curve, even if the object being photographed is the same object.

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Magnetic Dip

Magnetic dip is the angle between the horizontal and Earth’s magnetic field. A compass needle, for example, will not point north and south, but will also have a dip. It tends to dip at an angle toward the Earth (and to the sky). The dip is generally greater toward the pole.  At various locations close to the equator (but not exactly at the equator), the dip is zero.

Magnetic dip as observed on various locations on Earth can only happen if the Earth is spherical.

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Airborne Early Warning & Control (AEW&C): Mitigating Limited Radar Range Due to Earth’s Curvature

An AEW&C (airborne early warning and control) system is a radar system attached to an aircraft. It can detect objects at a very long range compared to any surface mounted radar system.

The reason is that Earth’s curvature limits the range of a surface-based radar. An airborne radar system mitigates this problem.

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The Dip of the Horizon

There are two kinds of the horizon:

  • Astronomical horizon: the horizon at the eye level.
  • True horizon: the line that visually divides the Earth and the sky.

Because the Earth is a sphere, the true horizon always lies below the astronomical horizon, or the eye-level. The angle between them is the dip of the horizon. The higher the observer, the larger the dip of the horizon.

Flat-Earthers claim there’s no dip of the horizon. They are wrong. It is not hard to observe the drop of the horizon and prove the curvature of the Earth.

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Crow’s Nest on Ships

A crow’s nest is a structure in the upper part of the ship, especially old-fashioned ones. It is used as a lookout point and positioned high above to increase visibility over the curvature of the Earth.

On the deck of a ship 4 m (13 ft) above the surface of the ocean, an observer can spot a 20 m (66 ft) high ship from at most ±25 km (16 mi). On the other hand, from a 35 m (115 ft) high crow’s nest, an observer will be able to spot the same ship from ±40 km (25 mi) away.

On modern ships, the role of a lookout is replaced by radars. And for the same reason, a radar is positioned in the upper part of a ship.

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Shadow on Clouds

Before sunrise or after sunset, the Sun is below the horizon and not directly visible. But the sky and clouds above are illuminated because they are high above, and sunlight can reach them.

If there’s a mountain between the Sun and the clouds, it can cast a shadow on the clouds. The flat-Earth model assumes the Sun is always high above, and thus, this phenomenon cannot possibly occur in a flat-Earth.

The fact that a mountain can cast its shadow on clouds far above it is evidence that the Earth is spherical.

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A Glass of Water

The surface of the water in a glass of water is practically flat. Some flat-Earthers claim this is ‘evidence’ that the surface of the water is flat, and it will always be flat no matter how wide the container. They are wrong.

If the Earth is a sphere with the radius of 6371 km (3960 miles), then the surface of the water in a 10 cm (4 in) wide glass will have a bulge of 0.00000002 cm as the result of gravity, excluding other effects like the surface tension.

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Evidence of Curvature: Turning Torso Building, Malmö, Sweden

Turning Torso is a 190 m (623 ft) high building in Malmö, Sweden. It is situated near the strait of Øresund. At the other side of the channel lies the city of Copenhagen, Denmark, only 15 km (9 miles) away from Malmö. Turning Torso has a distinctive segmented shape that is easy to recognize from far. And more importantly for our purposes, the segmented form is making it easy to judge its height from far.

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