James Cook’s Second Voyage

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The second voyage of James Cook was commissioned to search for the hypothetical continent Terra Australis in the Southern Pacific Ocean.  He explored the Pacific and Atlantic oceans in the process and proved there is no such continent unless it is over the South Pole itself, which we now call Antarctica.

Some sources stated that Cook traveled over 60000 miles in his second voyage. Flat-Earthers use the figure as Antarctica’s circumference and claim it as “evidence” that Antarctica is much more than a continent. In reality, James Cook explored the vast ocean and did much more than just circumnavigating Antarctica.

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Uniform Circular Motion

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The motion of a specific location on Earth due to Earth’s rotation is a uniform circular motion. We can separate it into a uniform linear motion and a centripetal acceleration toward Earth’s center. From the reference frame of an observer on Earth, the latter results in a constant centrifugal acceleration, which is felt simultaneously with Earth’s gravitational acceleration.

We often use the uniform linear motion of everyday objects to explain the effect (or the lack of thereof) of uniform motion of Earth’s rotation. Flat-Earthers incorrectly reject it just because “it is not a circular motion unlike Earth’s rotation” In reality, a uniform linear motion is one component of a uniform circular motion. And these explanations are correct and still apply.

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Nautical Almanac

A nautical almanac is a publication that describes the positions of stars to enable navigators to use celestial navigation to determine their position at sea. Because the positions of stars are not fixed, a nautical almanac needs to be continuously revised.

Flat-Earthers claim that the positions of stars are fixed, and they only circle the celestial pole. In reality, stars’ positions do change, and we can find the historical positions of various stars from old publications of a nautical almanac.

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Airplanes Do Correct for the Coriolis Effect

Airplanes do correct for the Coriolis effect. They constantly make adjustments to counter forces that try to push them away from the planned route, including the Coriolis force.

Flat-Earthers claim the Coriolis effect does not appear to affect airplanes, and they use it to “prove” that Earth is stationary. In reality, the Coriolis effect does affect airplanes, and we do have to correct for it. But the effect is tiny, and we can safely ignore it in flight planning.

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Sydney-Johannesburg Flight Route

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The existence of the non-stop Sydney-Johannesburg flight route is only possible if Earth is a sphere. We can find that out by comparing its duration to the same route but with a stop.

There are other Sydney-Johannesburg flight routes, but with a stop, like in Dubai. Flat-Earthers use the existence of these routes to “prove” a flat Earth. In reality, it does not mean the non-stop route does not exist & it is not difficult to verify that the non-stop route exists.

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Moving Vehicle Analogy: Inside vs Outside of the Vehicle

The moving vehicle analogy is often presented to explain how Earth’s rotation does not seem to affect an object’s motion. Similarly, a ball released inside a moving vehicle will not fall rearward because it retains its inertia.

Flat-Earthers offer the moving open-air vehicle as if it is the “correct ” analogy. In reality, with their analogy, the air moves relative to the vehicle, which exerts an additional force that does not exist in the fact being explained. Their analogy fails to represent the fact being explained.

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Bonneville Salt Flat and Earth’s Curvature

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Interstate 80 traverses the Bonneville Salt Flat, Utah, in a practically straight segment. From the hilly terrain to the west of the highway, we can observe the highway’s curve following Earth’s curvature using a long-zoom camera.

Flat-Earthers incorrectly claim that salt flats are perfectly flat and use them to “prove” a flat Earth. In reality, salt flats form a curve following Earth’s curvature, like the ocean’s surface.

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Polar Circumnavigation

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Polar circumnavigation is complete navigation around Earth through both the North Pole and the South Pole. Several parties have successfully done it, and it is only possible if Earth is a sphere.

Flat-Earthers incorrectly claim that Earth circumnavigation has never been done through both the poles, and they use it to “prove” a flat Earth. In reality, many have successfully done such feats.

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Hill Sphere

The Moon orbits the Earth —not the Sun— because the Moon lies well within Earth’s Hill sphere. Hill sphere is the region around Earth where Earth —instead of the Sun— dominates the attraction of satellites.

Flat-Earthers noticed the Sun exerts a stronger pull to the Moon than Earth does to the Moon. They incorrectly concluded that according to science, the Moon should orbit the Sun, then proceeded to use it to discredit science. In reality, they did not account for the centrifugal acceleration resulting from the motion around the Sun, which is one of the factors that determines Earth’s Hill sphere.

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Flight Routes During the COVID-19 Pandemic

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During the COVID-19 pandemic, many flight routes are being canceled, suspended, or cut down due to lockdowns, travel warnings, travel bans, or insufficient demand. These include flight routes that are impossible if Earth were flat.

Flat-Earthers looked for these routes, and when they could not find them, they use the lack of these routes to “prove” Earth is flat. In reality, they made these lookups during the COVID-19 pandemic, when most of these routes are not available or severely cut down.

Flying a Drone Inside a Moving Vehicle

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If we fly a drone inside a vehicle that is moving in a constant speed and direction, the drone will hover normally because it preserves the motion it gets from the vehicle. It will not abruptly move toward the rear of the vehicle.

Flat-Earthers claim that it should not be possible for drones to hover if Earth is rotating. In reality, drones follow Newton’s first law of motion and will preserve their inertia. It is easy to demonstrate the phenomenon by flying a drone inside a moving vehicle. The fact that drones can hover still in mid-air is not evidence of stationary Earth.

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Airplanes and Earth’s Rotation

An airplane exists on Earth. It has the same motion as the surface of the Earth, including Earth’s rotating motion. The motion and speed of an airplane are measured relative to Earth’s surface.

Flat-Earthers claim that an airplane should not be able to fly eastward or land. In reality, an airplane is moving relative to the surface. It has Earth’s motion as a component of its motion and does not need to chase Earth’s rotation.

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Earthshine and Moon Phase

Earthshine is a glow in the dark areas of the Moon because sunlight reflects off Earth’s surface to the Moon’s night side. Earthshine can be easily observed with long-exposure photography.

Some flat-Earthers claim that the Moon is transparent or that it is not a sphere. By observing the earthshine using a camera with the correct exposure, we can easily disprove such claims.

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Rock Balancing

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Rock balancing is an activity in which rocks are balanced on top of one another. It is possible to do it if Earth is rotating because the speed is constant and the rocks are affected by a constant net acceleration from gravity and Earth’s rotation.

Flat-Earthers use rock balancing as “evidence” that Earth is stationary. In reality, it is possible to balance objects on a moving platform, as long as it is moving in a straight line with a constant speed, and there is no force —like wind, affecting it.

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Our understanding of gravity explains a phenomenon clearly and directly. It is one idea, easy to understand, explains so many phenomena, can account for a large amount of data, and answers many questions. In other words, we can say that gravity is elegant.

In contrast, each of the different concepts in the flat Earth model requires a separate explanation and often in conflict with each other. We can say it is ugly. It is why flat-Earthers cannot accept that a single idea of gravity can explain so many phenomena.

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Negative Parallax

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Stellar parallax is the apparent shift of closer stars against more distant stars due to the orbiting motion of Earth. Negative parallax, or stars going the wrong way— occurs due to measurement errors placing the nearer star as the farther one and vice versa.

Stellar parallax directly proves Earths’ motion around the sun, and flat-Earthers use negative parallaxes to dismiss it. In reality, negative parallaxes are just statistical uncertainties.

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“What is Gravity”

In a StarTalk episode, Neil deGrasse Tyson was given the question “what is gravity?” He quipped “we have no idea” before elaborating more. Flat-Earthers quoted it out of context to discredit Neil and gravity, completely disregarding what Neil explained afterward.

In reality, Neil did provide a very comprehensive answer to the question “what is gravity” but flat-Earthers only gave an emphasis to the “we have no idea” part of his answer, and skipped the rest of his answer.

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Apparent Size of the Sun & the Moon

The Sun and the Moon appear about the same size in the sky, but they are not perfectly the same size, and their sizes are not constant because their orbits are not perfectly circular.

Flat-Earthers claim it is too much of a coincidence that the Sun is perfectly 400× larger than the Moon and perfectly 400× farther, making them appear perfectly the same size. In reality, the Sun and the Moon are not perfectly the same size in the sky.

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Interlaced Video and Deinterlacing

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Interlaced video is a technique for doubling the perceived frame rate of a video display without consuming extra bandwidth, especially with older display technology. With an interlaced video, a video frame is rendered twice, one after another, first for the odd-numbered lines and then for the even-numbered lines.

Flat-Earthers discovered objects appearing transparent in some footage from the ISS and use the fact as “evidence” the footage was faked. In reality, some of these artifacts are due to interlacing and the process of deinterlacing interlaced videos.

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Pressure Difference Without a Barrier

Atmospheric pressure decreases as altitude increases. A pressure difference can occur without a barrier. Other factors, like gravity, can cause a pressure difference.

Flat-Earthers claim a pressure difference cannot possibly occur without a barrier, like Earth’s atmosphere next to the vacuum of space. In reality, it is not difficult to demonstrate that a pressure difference can exist without a barrier.

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