Flerfraction

Atmospheric refraction generally raises the apparent position of astronomical objects near the horizon, as well as causing a slight vertical compression

Atmospheric Refraction is the bending of light within Earth's atmosphere due to variations in air density. Flerfs generally have no clue how atmospheric refraction actually works, so they use it (flerfraction) to explain phenomena which are actually impossible on a flat Earth, such as:

• sunsets/rises and moonsets/rises
• why stars can't be seen from particular locations (e.g. Polaris from the southern hemisphere)
• why objects beyond the horizon are obstructed
• why the horizon appears below eye level
• the existence of the south celestial pole
• why the sun and moon do not change in angular size
• star trails always being perfectly circular

Not all flerfs use flerfraction to explain the above phenomena; those who don't generally invoke flerfspective.

Flerfs often deny the presence of refraction when presenting observations of "missing curvature", while simultaneously using it to explain observations that are impossible on flat Earth. This is an example of the Third Law of Flerf.

Atmospheric "Magnification"

Many flerfs claim the atmosphere can magnify things like a magnifying glass. This is partly because they think the term "atmospheric lensing" (which generally means the same thing as atmospheric refraction) literally means the atmosphere acts like a bioconvex lens. Flerfs use this to explain why objects can appear obstructed by the horizon.

In reality, there is no mechanism by which the atmosphere can act this way. Because gravity causes air density to change as a function of height, objects can only appear to be compressed (or stretched in rare cases) in the vertical direction. Some flerfs propose the mechanism for atmospheric "magnification" is water droplets in the air. While a singular water droplet can act like a lens, flerfs don't realise that a collection of many water droplets does not equal one big lens.

Walter Bislin's Flat Earth Dome Model

Walter Bislin's model showing the impossible paths light would have to take.

Flerfs have plagiarised Walter Bislin's Flat Earth Dome Model, claiming it is a working model of flat Earth. In reality, the simulation shows how light would need to bend in impossible ways for flat Earth to make any sense. Flerfs that subscribe to this model believe the light bending is made possible due to flerfraction and/or some firmament-related magic.

Useful Resources

Resource	Author	Notes
Stellarium	See developers	Astronomy software which factors in standard atmospheric refraction when calculating the apparent position of astronomical objects.
Simulation of Atmospheric Refraction	Walter Bislin	Comprehensive calculator for terrestrial refraction. Shows a visual comparison between globe Earth and flat Earth predictions.
Advanced Earth Curvature Calculator	Walter Bislin	Comprehensive calculator for earth curvature, with the option to factor in atmospheric refraction.
Metabunk Refraction Simulator	Mick West	See how temperature profile affects refraction in the atmosphere.