[bizerl (OP)]

When we look at rainbows, we see a thin band of visible light from red to violet(ish). How many frequencies exist in a rainbow either side of the visible light spectrum? Is there a band of infrared light around the perimeter or some sort of horrible, UV, ionising band in the middle somewhere?

Also, sometimes if a rainbow is very defined, I can see a sort of yellowish haze inside the violet band. Is this the inside version of the usually outside double rainbow?

[Geezer]

Great question!

I kinda-sorta think the answer is yes, but let's see what the experts say.

(This question probably belongs in the physics forum - I'll move it there for now.)

[RD]

... How many frequencies exist in a rainbow either side of the visible light spectrum? Is there a band of infrared light around the perimeter or some sort of horrible, UV, ionising band in the middle somewhere?

Water absorbs UV and IR much more strongly than visible light ... http://www.lsbu.ac.uk/water/vibrat.html#uv
So the far-UV and far-IR components to a rainbow are going to be very dim.

... I can see a sort of yellowish haze inside the violet band. Is this the inside version of the usually outside double rainbow?

sounds like you're seeing some supernumerary bands ... https://secure.flickr.com/photos/kiwinz/5109305087/  which is an interference pattern, (whereas the rainbow itself is created by dispersion).

The "outside rainbow" cannot occur in contact with the inner rainbow ... https://en.wikipedia.org/wiki/Alexander%27s_band