## Difference in Hidden Height Calculation Results

Flat-Earthers use “8 inches per mile squared” to calculate the hidden height of a distant object. It is not the proper formula as it ignores the observer’s height & refraction. It will result in an erroneously larger hidden height than the correct amount.

A 2-m-tall observer will be able to see a 5-m-high object at 10 km. However, the 8-inches rule erroneously tells it should be entirely hidden. It is the source of a lot of flat Earth misinformation.

## First Image of Earth From Space Taken By a V-2 Rocket

The first image of Earth from space was taken by the V-2 No. 13 rocket in 1946 using the DeFry 35mm movie film camera and a 50mm lens attached to the rocket. The camera had a relatively narrow field of view. As a result, Earth’s curvature is only very slightly visible.

Flat-Earthers claim the flat appearance in the photo “proves” a flat Earth. In reality, 1. by careful examination, we can see the curve, 2. the camera has a narrow field of view, reducing the visible curvature, 3. the photo shown by flat-Earthers is usually a cropped version, further reducing the visible curve, and 4. the photo matches the expected curvature according to simulation.

## Curved Airplane Window and Observation of Earth’s Curvature

With careful planning, we can easily observe Earth’s curvature from an airliner. To “explain” the observation, flat-Earthers invented the excuse that it is caused by the distortion from the shape of the airplane’s window.

In reality, all camera lenses are curved, too, yet most of these lenses produce normal, rectilinear images. The fact that the shape of the window is curved does not mean looking through the window will produce a curved horizon.

## Bonneville Salt Flat and Earth’s Curvature

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.

## Earth’s Curvature and the Size of a Coronavirus SARS-CoV-2 Causing the COVID-19 Outbreak

The surface of the water in a container with a width of one meter (3 ft) will have a curvature of 0.000002 cm from Earth’s gravity. As a comparison, a single SARS-CoV-2 coronavirus is at least 0.000005 cm in diameter, or at least 2½ times larger.

If a SARS-CoV-2 coronavirus is not visible to the naked eye, then there is no reason to expect that we will be able to see the much smaller curvature of the surface of water.

## Dizzib’s Earth Curve Calculator

Dizzib’s Earth Curve Calculator is one of the most popular Earth’s curvature calculator on the Internet. However, it does not account for atmospheric refraction and, therefore, unsuitable for determining the visibility of a distant object.

Many flat-Earthers used Dizzib’s calculator to analyze the observation of the visibility of a distant object and led them to an erroneous conclusion. If we can spot the calculator being used in their images, we can easily rule out their conclusion.