Water bends light, which makes a straight straw in a glass look broken or shifted.

The longer version

Light slows when it enters water, and a beam crossing the boundary at a slant changes direction. Rays leaving the submerged part of a straw therefore arrive at the eye from slightly displaced angles, and the brain, assuming straight-line travel, places the underwater section where it is not.

The effect makes pools look shallower than they are, a misjudgement with real consequences for anyone diving in. Refraction also magnifies, so a coin under a glass of water can appear larger. Fishermen aiming at fish and astronomers correcting for air rely on the same correction, and both learned it by trial long before the mathematics was written down.

Where this entry sits

These facts explore how light behaves and how human eyes turn it into the colors we see. Along the way you meet rainbows, prisms, mirrors, shadows, lasers, and optical tricks that fool our vision every day. The full list sits on the Color and Light page, where every entry is listed in order.

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More From Color and Light

Eight more entries

Mirages appear on hot roads when layers of air bend light from the sky toward the ground.

A rainbow is actually a full circle, but the ground usually hides the lower half.

Double rainbows happen when light reflects twice inside each droplet, reversing the color order.

You never see a rainbow from directly overhead because the geometry requires looking away from the sun.

Red light bends least through glass, while violet light bends the most.

The color orange takes its name from the fruit, which had the word first.

Purple and violet describe similar hues, though violet refers to a single wavelength of light.

Many languages have fewer basic color words than English, sometimes grouping blue and green together.

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