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Pictures

rainbow in river not a reflected rainbow

Bigger versions : First | Second

On this one we see the other side of the "main" arc and the white surface of water (see below).

other side of rainbow

Observations

So I observed these rainbows in a calm river. Like classical rainbows, the phenomenon requires the sun and creates a circle of colors at roughly 42 degrees to sunlight direction (I didn't measure), and there are also 2 visible arcs.

Surprisingly though, the "less visible" arc was inside the "main" arc, and they didn't seem to share the same center.

Note also that it's not simply a reflected rainbow since the air was rather dry as you see in the second image.

At the surface of the water, I found numerous leaves and a dirty film that leaves a brown thin substance on immersed objects. No idea what it is, but it's common when there's no wind and a small flow in the river (and doesn't usually create rainbows !).

Last but not least, it was late in the morning but I could see some places with white frozen morning dew in spots of grass still in shadows. The surface of water wasn't frozen, but appeared "pearly" and white if seen from a low incidence.

Question

Is this phenomenon created by reflections and refraction of light in water dropplets, like in rainbows ? If so, how can we explain the presence of droplets, and the differences with usual rainbows, i.e. non-concentricity of arcs and the "secondary" arc inside the "main" one ?

Thanks in advance !

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    $\begingroup$ Well explained here? atoptics.wordpress.com/tag/water-surface $\endgroup$
    – Farcher
    Dec 15, 2016 at 18:25
  • $\begingroup$ Exactly ! My previous web searches didn't include "dew" sadly. The explanations in your link are convincing. If I may add a new question : If dew droplets aren't spherical, due to being in contact of a surface (assuming flat), we can expect the resulting arc to be deformed right ? i.e. not purely circular ? $\endgroup$ Dec 15, 2016 at 20:07
  • $\begingroup$ If the drops are small they will be close to being spherical. $\endgroup$
    – Farcher
    Dec 15, 2016 at 21:10

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No helpful answer. But I observed a double rainbow on the oceans surface. So not stagnant water and not dewy as it wasn’t raining. It was a normal warm day in one of the US Virgin Islands. Did you ever find an explanation?

enter image description here

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