Why the second rainbow has its colours reversed

Look closely at a double rainbow and the second arc begins to seem less like an echo. It is usually fainter and sits outside the brighter bow. Its colours also run the other way. That reversal tells you something about the route the light took through the rain.

One extra reflection changes the view

Sunlight bends as it enters a water droplet and again as it leaves. The National Weather Service’s explanation distinguishes the primary rainbow, whose light reflects once inside a drop, from the secondary rainbow, whose light reflects twice. These are different paths through the water, not two separate coloured objects hanging in the sky.

The extra reflection changes the directions in which the light emerges. That is why the secondary bow occupies a different part of your view. It is not simply the primary rainbow projected a little farther away.

Read from the outside edge inward

For the brighter primary bow, the outer edge is red and the inner edge violet. The NASA Space Place explanation published by NOAA describes the secondary bow with violet outside and red inside. Its two-reflection route also produces a fainter bow.

A useful visual check is to find the red edges: in an ordinary double rainbow, they face the space between the two arcs. The violet edges face away from that gap. This is a way to remember the arrangement, not a requirement that every hue be equally clear in a photograph.

There are no hard boundaries between seven painted stripes. As the Met Office explains, the colours form a continuous spectrum. Familiar colour names help us describe it; they do not divide sunlight into seven separate compartments.

The observer belongs in the explanation

The viewing arrangement matters. For a sunlit rainbow, the Sun is behind the observer and rain is ahead. The National Weather Service gives approximately 42 degrees for the primary bow and around 50 degrees for the secondary. These describe angular geometry, not a distance to a rainbow’s supposed endpoint; individual colours do not all follow one exact angle.

That also helps explain why chasing a rainbow’s end is the wrong picture. NOAA’s account describes a rainbow as an optical phenomenon whose appearance depends on where the viewer is standing. It is not a fixed arch that you could walk underneath and inspect from every side.

Notice the quieter space between the bows

The gap can look darker than the neighbouring sky. The Met Office calls this Alexander’s band. The word darker is relative: it does not mean the strip contains no light or must look black. Cloud, rain and the surrounding brightness remain part of the scene.

A short observation checklist

When a double rainbow is visible, compare three things: which arc is brighter, which red edge faces the gap, and whether the sky between the arcs looks darker. Record what you can actually distinguish rather than filling in an expected set of colours. Our illustration shows the general arrangement; it cannot establish the brightness or geometry of any real sighting.

The droplets themselves have another easily misread feature. Read why falling raindrops are not shaped like teardrops.

References

Met Office. (n.d.). Rainbows: Optical wonders. https://weather.metoffice.gov.uk/learn-about/weather/optical-effects/rainbows
NASA Space Place. (2025, September 2). What causes a rainbow? NOAA National Environmental Satellite, Data, and Information Service. https://www.nesdis.noaa.gov/about/k-12-education/optical-phenomena/what-causes-rainbow
National Weather Service. (n.d.). How do rainbows form? https://www.weather.gov/fgz/Rainbow

Reading notes and scope

Sources checked 29 September 2026. NWS is part of NOAA, so those two sources are not independent corroboration; the Met Office offers a separate explanation. This is a qualitative optics guide, not field measurement. No source photographs are reproduced.