A rainbow forms when sunlight bends and reflects inside water droplets, separating into colors that reach your eyes at different angles. For the familiar primary rainbow, sunlight is behind you and the droplets are ahead.
A raindrop changes light’s direction
The Met Office explanation follows the light into a drop, through an internal reflection, and out again. Refraction—the bending as light passes between air and water—helps separate its colors.
The result depends on the positions of the light, droplets and observer. Think of a rainbow as a viewing geometry rather than a painted stripe fixed to one place in the landscape.
The second bow reverses the colors
A secondary rainbow involves an additional internal reflection. It appears outside the primary bow and is usually fainter. Its colors run in the opposite order. The National Weather Service’s atmospheric-optics guide describes the outer secondary bow and its reversed spectrum.
That gives you something specific to notice in a photograph: compare the order of colors in the two arcs. A second bright band is more interesting when you can explain what makes it different.
Why the arc can become a circle
The Met Office notes that a rainbow’s full circle can sometimes be seen from an elevated viewpoint when the right droplets and light are present. From the ground, the lower part is usually hidden.
For a simple observation journal, describe the scene before reaching for a dramatic caption: was there one bow or two, which one was brighter, and where was the sunlight coming from? Record what you can actually see. If the second bow is too faint to resolve its colors, say so.
Those questions are more useful than trying to count seven perfectly separate stripes. The familiar color names are convenient labels for a continuous spectrum.
This is a suggested observation exercise, not a forecast of where a rainbow will appear. Enjoy the view from a safe place; a photograph can be enough to investigate later.
Keep looking upward with why the sky is blue and why sunsets turn orange.
