sol

Солонгын өнцөг

Explore the geometric-optics angles behind primary and secondary rainbows.

Drop ray sketch

Ray display
Parallel rays entering a spherical water drop A schematic circle showing many parallel rays refracting and reflecting through a water drop.

Many parallel rays are sampled across the drop. Where the outgoing family bunches together, the rainbow direction is forming.

Deviation angle curve

Deviation angle versus impact parameter A curve showing signed rainbow deviation angle as a function of normalized impact parameter.

Current angle

A negative signed angle follows the source notebook convention: it is counted from the Sun. Positive angles are measured from the antisolar point.

Primary and secondary summary

What is plotted?

The impact parameter b/R is the normalized height where a parallel ray enters the droplet. The incident angle α follows from b/R = sin(α). Order 1 is the primary rainbow, order 2 is the secondary rainbow, and higher orders add more internal reflections.

Uniformly spaced rays in the sketch correspond to uniformly spaced b/R values on the curve. Extrema mark where nearby rays bunch together, producing a bright rainbow direction.