Wish I’d had a camera at the time
but a cartoon will have to suffice,
representing two actual incomplete rainbows
that stop in midair where they meet,
lit only by a setting sun.

[![](https://i.stack.imgur.com/Mw2BJ.png)](https://i.stack.imgur.com/ry5zb.png)

This seemed so paradoxical,
I honestly wondered if it was a dream.
After all, on a normal
[rainbow with two arches](https://en.wikipedia.org/wiki/File:Full_featured_double_rainbow_at_Savonlinna_1000px.jpg),
the arcs do not touch
and the larger one is very much fainter with a reversed spectrum.
The arches schematized here were indeed accompanied by
typically-faint concentric larger arcs
that also stopped abruptly where they, too, met,
exactly above the main meeting point.

Being awake, as it turned out,
I discovered the simple explanation for this,
related to an often-subtle
and less dramatic everyday phenomenon
that is readily understandable in nonscientific terms.
I had enough information at the time
to solve this like a puzzle, though,
and now you do too.

**What was that simple explanation for this odd pair of rainbows?**

**Notes.**
Only air was between the point of view and these rainbows.
The less complete rainbow, to the right, is *slightly* brighter
and both arches brighten the air directly below them.
The picture has been **revised** to more clearly represent
how the rainbows end at slightly different places, muddled by their overlap.

The larger arch ends
a little to left (and slightly up) from where the smaller arch ends.

The rainbows were not as thick as depicted (none are)
and had further characteristic features
that scientific photography would reveal
to extend a vertical pattern of similar meeting points.

Safe to guess that this effect was not observed
by humans more than a century or two ago,
although tiny animals may have experienced it
over the course of eons.

Some details of the real-life story have been altered
in an attempt to stymie internet searches.

Here is an **added** diagram meant to emphasize
that the position of a rainbow depends on the direction of
incoming sunlight
and
that the size and distance of any rainbow are intrinsically ambiguous
because the mist that creates a rainbow is rarely at a single
distance and the resulting image occupies the same portion of
the visual field
regardless of actual distances to individual mist droplets.
More information can be found all over the internet,
such as
[Wikipedia](https://en.wikipedia.org/wiki/Rainbow)
and (less laboriously)
[earthsky.org](http://earthsky.org/earth/what-gives-rainbows-their-curved-shape).

[![](https://i.stack.imgur.com/JjENf.png)](https://i.stack.imgur.com/JjENf.png)