Blue Marble and the Visible Area of Earth’s Surface

The Blue Marble is an image of Earth taken by the crew of the Apollo 17 spacecraft on its way to the Moon. It was taken from a distance of 29000 km from Earth’s surface.

Flat-Earthers dismiss it by incorrectly asserting that the image covers a too-small area of Earth’s surface, due to their failure to account for the maps’ distortion.

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The Polar Azimuthal Equidistant Map is NOT the Flat Earth Map

The azimuthal equidistant map is a valid map. The map is a projection of the spherical Earth. Like every other map, it has distortions. It is not the “flat-Earth map,” and the usage of the azimuthal equidistant map does not endorse a flat Earth.

Flat-Earthers claim the shape of the polar azimuthal equidistant map as their own “flat-Earth map.” It is identical with the azimuthal equidistant map only in shape, but not in everything else. Unlike the azimuthal equidistant map, the so-called “flat-Earth map” does not represent reality.

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Air Map of the World 1943/1945

Flat-Earthers discovered a map titled “Air Map of the World” from 1943, explaining the flight routes during the time. Because the shape is identical to the fictional “flat Earth map,” they incorrectly claimed that it is a flat-Earth map. In reality, it is an azimuthal equidistant map that has distortions, a flattened shape of the spherical Earth on a flat surface, and does not depict the true shape of the Earth.

The exact nature of the map is even explained in a very detailed manner in the map’s description. Unfortunately, in the flat-Earth community, the map is passed around in a very low resolution, and therefore, the explanations become unreadable.

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Fisheye Videos

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In images taken using a fisheye lens, a straight line will remain straight if it crosses the center of the image. We can use this attribute to determine if a line is straight in reality.

In any fisheye videos taken from a high altitude, there should be plenty of moments where the horizon crosses the center of the image, and we can use those to determine that the horizon line is curved in the real world.

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Excessively Defishing Fisheye Images to Flatten the Curved Horizon

Defishing is a process for removing barrel distortions in fisheye images. It takes fisheye images, and convert them to normal, rectilinear images that preserve straight lines. Different fisheye lenses can have a different amount of distortions, and thus, require a different defishing strength.

Some flat-Earthers would deliberately use stronger defishing parameters than necessary for the lens being used. Their intention is not to remove the barrel distortion in the resulting images, but also to introduce pincushion distortions to the images. Pincushion distortion is the reverse of barrel distortion. It would curve a straight line to the other direction from what would be produced by the barrel distortion in fisheye lenses. At a specific position in the scene, it would make the curved horizon to appear flat.

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The Reasons Why Fisheye Lenses Are Used

Action cameras are being used in high-altitude balloons, rocket launches, and the ISS because they have some advantages compared to other cameras. And most action cameras are equipped with a fisheye lens.

Flat-Earthers allege that there is an evil intention behind every use of fisheye lenses, especially in space and high-altitude usages. They are wrong. The use of fisheye lenses is not unreasonable. And if a rectilinear result is desired, it is trivial to convert any fisheye footage to a rectilinear one.

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The Gleason Map

The “Gleason Map” is a map with the azimuthal equidistant projection, centered on the north pole. The Gleason Map is not a scaled-down figure of the Earth, but it is merely a projection of the actual, spherical shape of the Earth, like every other map.

Alexander Gleason —the creator of the map— claimed that the map depicts the shape of the ‘flat Earth’. The majority of the flat-Earth communities adopt this map as ‘the flat-Earth map.’ They are wrong. The map is merely a projection of the spherical shape of the Earth, just like every other map types.

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Day and Night Areas on a Flat Earth

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At any given time, there is an equal area of the Earth that is experiencing daytime, and that is having a night time. The reason is that the sun is very far, and it would illuminate a hemisphere of the Earth, and leave the other dark.

If we plot which areas of the Earth that are getting sunlight on an azimuthal equidistant map centered on the north pole, the sun would appear to illuminate a somewhat elliptical area during the northern hemisphere summer, and a lopsided Bat-Signal shaped area during the winter. During the equinox, the sun would appear to illuminate a half-circle area.

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Fisheye Lenses and Earth Curvature

A good majority of pictures of Earth taken from space are being dismissed by flat-earthers merely because they are made using fish-eye lenses. They believe any curvature of Earth shown in those pictures is the result of the fisheye effect, and thus, cannot be used as evidence of Earth’s curvature. They even take a step further and assume a fish-eye lens is deliberately used to take every picture of the Earth taken from a high altitude so that they would have a curvature in it.

These claims are, of course, ungrounded. In some cases, we can conclude the curvature is there, even when a fish-eye lens is being used. We can use this useful property of any photographic lens:

A straight line will appear straight as long as it crosses the center point of the image.

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