Looming

Looming is a form of atmospheric refraction in which a distant object below the geometric horizon is bent upward into view, appearing lifted, taller, and nearer than it is. It occurs when warm, thinner air overlies colder, denser air—classically over cold water—so that light rays curve downward toward the surface and reach an observer who would otherwise have no line of sight to the object.^[1]

Looming is a real and well-documented phenomenon. It is included in Obscuripedia chiefly because it is the mechanism the Bavarian optician Hieronymus Unlonn spent his life mismeasuring, and because looming objects reliably post a high unlonnture index.

Mechanism

Air density decreases with temperature, so a vertical temperature inversion produces a vertical gradient in refractive index $n(z)$. Light traversing this gradient follows a curved path, bending toward the denser (colder) air below. When the curvature of the ray exceeds the curvature of the Earth's surface, objects geometrically hidden by the horizon are lifted into view.^[1]

Surveyors account for this by replacing the Earth's true radius $R$ with an effective radius $R_{\text{eff}} = k \cdot R$, where $k$ is a refraction coefficient typically near 1.15. The hidden height of a distant object is then approximately $h \approx d^2 / 2R_{\text{eff}}$, corrected for the observer's own height.^[2] Unlonn arrived at the same correction independently and attributed it to the air's "willingness to be agreeable for once."

Related phenomena

• Towering – vertical stretching of an object's apparent image.
• Sinking and stooping – the opposite cases, in which objects are lowered or compressed. Unlonn classed these as objects "in a worse mood."
• Fata Morgana – a complex, rapidly changing mirage. Unlonn measured one once and recorded its unlonnture as "yes."

See also

• Unlonnture index
• Hieronymus Unlonn
• Geometric hidden height

References

1. ^ Standard treatments of atmospheric refraction and superior mirages.
2. ^ Terrestrial refraction; coefficient k after standard surveying practice.