Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: thedoc on 23/09/2016 11:23:04

Title: Do waveforms beyond the visible spectrum form rainbows?
Post by: thedoc on 23/09/2016 11:23:04
Sarah Turnbull asked the Naked Scientists:
   Hello Naked Scientists,

The other day I was looking at a rainbow, and then later I was looking at a microwave. I suddenly wondered: If we were able to somehow enhance our eyes in order to see beyond the visible spectrum, would we see microwave and UV stripes in the rainbow? Do all the wavelengths form stripes like visible light does?
Sarah (Castlemaine, Australia)
What do you think?
Title: Re: Do waveforms beyond the visible spectrum form rainbows?
Post by: evan_au on 25/09/2016 23:08:23
In principle, yes. This is how infra-red radiation was originally discovered.

The astronomer Herschel conducted an experiment where he broke up light into its constituent colors using a glass prism (like a small rainbow).
He used a thermometer to measure the amount of energy in each color, and compared it to the temperature when he placed the thermometer outside the visible band of colors.
He was astonished to see that the thermometer showed a higher temperature in the region beyond the red (infrared) than it did on visible colors. Eventually, it was discovered that the Sun puts out more energy in infrared than it does in visible light.

Although this works for infrared, raindrops won't bend microwaves as effectively, because water absorbs microwaves, and the size of raindrops is much smaller than the wavelength of microwaves.

A rainbow can only bend light which makes it through the atmosphere, and our eyes are fairly effective at picking up the shortest wavelengths that make it through the atmosphere. The atmosphere blocks most ultraviolet (and many kinds of glass also block ultraviolet). See the diagram at:
Title: Re: Do waveforms beyond the visible spectrum form rainbows?
Post by: Electron spin on 30/09/2016 03:04:54
I believe evan is right.

Nonetheless it is a good question.

If I understand your Q correctly, visible light is is simply a "slice" of the RF spectrum. Therefore, if we could expand our bandwidth via mechanical manipulation or the size, depth, and/or chemistry of our eyes like tuning a radio receiver to a different channel we would see below and above the visible spectrum like some critters do.

You see, visible light is just a piece of the "larger same"....a magnetic and electric field generally perpendicular and travels at c in the same medium through the same index of reflection, etc.

I would suggest to my students when trying to figure out the answer to a continuum question like this is to frame it relative to both extremes which would be DC and a freq so high that the wavelength might be a short as the diameter of a hydrogen atom or smaller..

Always take mathamatical based inquires to the extremes for ease of reasoning! ;)

This method saves time and heartache for many students, for many decades.

2nd Q:, "Do all the wavelengths form stripes like visible light does"?

Technically yes they do. play around with a spectrum analyzer.