Snell's Window

Plate 25 speaks for itself: “The whole sky, through a 97° hole.”

The Physics

Looking up from under water, the whole hemisphere of sky is squeezed into a circle bounded by the critical angle. Outside it you see total internal reflection of the water below.

θ_c = arcsin(1/n)

• θ_c: critical angle, °
• n: refractive index of water, dimensionless

n = 1.333: θ_c ≈ 48.6°, window 97.2°.

Sources

• E. Hecht, Optics, 5th ed., §4.7.

On the poster

Plate 025, “Snell's Window”: the pixel-art plate with its slogan “The whole sky, through a 97° hole.”, the key equation and the facts panel shown above. Pixelated Physics. Physics. Personified.