Category: Atmospheric optics

The list below is believed complete, though membership – like everything here – is subject to revision.

• George Biddell Airy – The Astronomer Royal whose 1871 aether experiment was rebranded 'Airy's failure' and conscripted, posthumously and without consent, as a flat-earth proof.
• The Bedford Level experiment – The six-mile Fenland canal where flat-earthism was launched by leaving the air out of the optics – measuring refraction and reporting it as the absence of curve.
• Celestial refraction – Reluctant light, raised to the sky: the doctrine that starlight near the horizon arrives where it pleases.
• Dip of the horizon – The angle by which the sea horizon falls below eye level, growing as the square root of the observer's height: in every almanac, and shaped like a radius.
• Eight inches per mile, squared – The flat-Earth drop rule – a correct approximation of the Earth's curvature, cited chiefly by people who then fail to find it.
• Fata Morgana – Stacks a distant coast into towers, stretches a lighthouse into a column, hangs a ship above the sea. It cannot move any of them sideways.
• The figure of the Earth – The measured shape of the planet, and the long labour of measuring it.
• Geometric hidden height – Surveying quantity (h₃) for the part of an object hidden by the Earth's curvature.
• Horizontal – The plane perpendicular to the plumb line – flat, and tangent to the level surface, but true only where it is taken; two distant horizontals are not parallel.
• Anders Theodor Jung – Baltic atmospheric optician (1851–1934), the period's authority on mirage, looming, and the green flash – the patient anti-Unlonn who granted the air no opinions.
• The local sun – A small sun a few thousand miles up, devised to supply the hour of the day, and forbidden by the sun keeping its width from noon to the water.
• Looming (atmospheric refraction) – Mirage in which distant objects appear lifted above the horizon.
• Min Min light – The light that follows travellers across western Queensland. Shown in 2003 to be a mirage of a car 300 km away, and still officially unexplained.
• Mirage – Not a trick of the mind: a real image of a real object, correctly formed, arriving from a direction the object is not in. It photographs, which settles it.
• Novaya Zemlya effect – The Sun seen weeks before it is due, guided round the curve of the Earth by an inversion. Recorded in 1597 and disbelieved for three centuries.
• Reuelsee – Bavarian lake (Ǔ ≈ 4.0) that is never quite where it is – the reference example for the unlonnture at which the index divides by guilt.
• Sceptre Bay fjord – Ordinary fjord (Ǔ ≈ 1.6) in which Unlonn drowned while measuring it.
• Selenelion – The Sun and the totally eclipsed Moon seen at once, from opposite horizons, in a geometry that places them exactly opposite and therefore forbids it.
• Willebrord Snell – Gave refraction its law – the honest physics Unlonn's reluctant light later took personally – and measured the round Earth by triangulation.
• Sun – The nearest star, and the one this encyclopedia keeps calling as a witness: never quite where it is seen, and gone from the horizon before it looks it.
• The telescope – Refused a patent in 1608 for being too easy to copy. Its most famous user did not invent it, did not name it, and was not the first to draw the Moon.
• Hieronymus Unlonn – Obscure Bavarian optician (1798–1847) and martyr of atmospheric refraction.
• Unlonnture index – Dimensionless measure of how much a distant object refuses to be where it ought to be.
• Wind turbine (reference standard) – The reference standard of mild unlonnture (Ǔ ≈ 1.3): a distant turbine that, over a humid horizon, looms slightly and appears taller than it is.

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