[thedoc (OP)]

Anthony leyland asked the Naked Scientists:
   A few days ago, just after sun down, we saw a pure red rainbow. I never knew these existed. I assume it's  down to the same reason we have red sunsets - that red light gets scattered less by the atmosphere. But I'd appreciate a more educated explanation!!
Thanks
What do you think?

[RD]

Same reason as the orangey rainbows, see ... http://www.thenakedscientists.com/forum/index.php?topic=18551.0  [reply #9]

If the sun had actually set the red rainbow would arc very high in the sky

[ A recent one in the UK ... http://www.telegraph.co.uk/news/2016/08/25/spectacular-red-rainbow-illuminates-historic-english-town--in-ph/ ]

[VanVinci]

Anthony leyland asked the Naked Scientists:
   A few days ago, just after sun down, we saw a pure red rainbow. I never knew these existed. I assume it's  down to the same reason we have red sunsets - that red light gets scattered less by the atmosphere. But I'd appreciate a more educated explanation!!
Thanks
What do you think?

Not so much down to the same reason but rather a result of a red sunset.

A rainbow is produced by raindrops functioning exactly like Newton's Prism.

Light enters the sunny side of a raindrop and is refracted or bent by doing so.

It then reflects off of the back inner wall of the raindrop and refracts a second time as it passes back out of the sunny side of the drop.

Newton discovered that a Prism will refract light of different wave-lengths by different angles. Resulting in 'White Light' fanning out into the ROYGBIV spectrum we all recognize.

So what happens when you only start with light of Red Wave-lengths???

[Colin2B]

So what happens when you only start with light of Red Wave-lengths???

If red's all you' e got, then red's all you'll get []