• Question: IS THERE AN INVISABLE COLOUR A EACH END OF A RAINBOW SOMETIMES I THINK THERE MAY BE INFRARED BESIDE VIOLET

    Asked by mspeirs96 to Anne, Carolyn, Joe, Mariana, Nick on 24 Mar 2010 in Categories: .
    • Photo: Nick Bradshaw

      Nick Bradshaw answered on 24 Mar 2010:

      Yes, in theory rainbows have infra-red at one end and ultra-violet at the other, although their is no way you should be able to see them.

      Also, you sometimes see a second whole rainbow slightly above the first one

    • Photo: Carolyn McGettigan

      Carolyn McGettigan answered on 24 Mar 2010:

      The rainbow that we see is limited by our visual system, which can only perceive light with wavelengths within a certain range (from red through to violet). The rainbow is produced by the refraction of white light into components with different wavelengths, and that’s how we see the different colours arranged side by side. However, we know that light from the sun contains UV light (ultra-violet, with wavelength shorter than visible violet) and infra-red light (wavelength longer than visible red light). So, in the rainbow, infra-red light would be refracted beyond the edge of the red band of visible light, not beside violet.

      There’s a good story as to how infra-red light was discovered. In 1781, Frederick Herschel wanted to test whether the warmth of sunlight was carried more by certain colours of light than by others. He used a prism to refract a rainbow onto a set of thermometers (one for red, one for orange, etc) and recorded the temperature from each. His control condition, which he didn’t expect to warm up, was a thermometer placed in the dark just outside the red edge of the rainbow. To his surprise, he found that this thermometer recorded the highest temperature – which was coming from the refracted infra-red light! This is the principle behind infra-red cameras, which pick up warmth in infra-red form coming from our bodies.

    • Photo: Joseph Devlin

      Joseph Devlin answered on 24 Mar 2010:

      I assume that the prism effect divides light into the full spectrum of wavelengths, even those beyond the range of the human eye. So I guess the answer must be “yes” and the old song should be revised to:

      Red and yellow and pink and green
      Orange and purple and blue
      ultra-violet and x-rays and gamma rays, too
      I can sing a rainbow
      Sing a rainbow
      Sing a rainbow too

Comments

  • Photo: Joe

    Joe commented on :

    It might be worth adding, that in addition to invisible rainbow colors, there is also a secret chord one can play to please the Lord, but you don’t really care for music, do ya?

  • modshamini commented on :

    Does it go like this: the 4th, the 5th…?

    Great story about how they discovered infra-red Carolyn. I love it when scientists get totally unexpected results and discover something completely new by accident!