Snell's window half-angle.

Underwater, the entire above-water hemisphere is refracted into a cone — the "Snell's window" or "optical manhole" — of half-angle \(\theta_c = \arcsin(1/n)\) (Johnsen 2012, ch. 5). For seawater (\(n \approx 1.333\)) this is about 48.6 degrees, so the whole sky is compressed into a ~97 degree cone overhead.

Usage

snells_window(n = 1.333)

Arguments

n

Refractive index of the water relative to air. Default 1.333. Vectorised.

Value

Half-angle of Snell's window, in degrees.

References

Johnsen S (2012) The Optics of Life. Princeton University Press, ch. 5.

See also

fresnel_reflectance, wavelength_in_medium

Examples

snells_window()        # ~48.6 degrees
#> [1] 48.60663