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📘 Why the secondary rainbow flips colors

Imagine standing at the edge of a shower with sunlight warming your back. Put the Sun behind you and look toward the rain. The bow is a pattern made by drops sending selected rays into your eyes.

3
lessons
~15 min
to learn
Adults
level
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What you’ll learn

  1. The bow begins behind youExplain how sunlight, spherical raindrops, and the observer's position produce the primary rainbow.A rainbow is a viewing pattern made by refraction, internal reflection, and color separation in many drops opposite the Sun.
  2. The second route through a dropDescribe the two-reflection path that produces a secondary rainbow and why it is wider and fainter.The secondary bow comes from a second internal reflection, sending fewer rays out at a larger angle.
  3. The dark space betweenIdentify Alexander's dark band as an angular gap between the primary and secondary ray concentrations.The dark interval is not a hole in the rain; it is where neither bow sends concentrated rainbow light toward the observer.

Questions this course answers

What extra event makes the secondary rainbow?

The secondary bow comes from rays that reflect twice inside a drop before emerging.

How does the secondary rainbow's color order differ from the primary's?

The outer bow has red toward its inside and violet toward its outside, opposite the primary order.

Why can the sky between the bows look darker?

The primary's concentrated rays end near 42 degrees while the secondary's begin near 51 degrees, leaving a darker interval.

Put the main events in a primary-rainbow ray path in order

The primary path is built from two refractions with one internal reflection between them.

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