Rainbows, raindrops & angles

About rainbows, raindrops & angles
How they interconnect
    • In any particular example of a ray of light passing through a raindrop, the angle of deviation and the angle of deflection are directly related to one another and together add up to 1800.
    • The angle of deviation is always equal to 1800 minus the angle of deflection. So clearly the angle of deflection is always equal to 1800 minus the angle of deviation.
    • In any particular example, the angle of deflection is always the same as the viewing angle because the incident rays of light that form a rainbow are all approaching on a trajectory running parallel to the rainbow axis.

Scattering: Raindrops

About scattering in raindrops
  • Scattering in raindrops obeys the laws of both reflection and refraction, commonly referred to as Snell’s law. Here are three related descriptions of what causes scattering when visible light strikes a raindrop:
    • When light of a specific wavelength strikes the surface and enters a raindrop its subsequent path depends upon the point of impact, and the refractive indices of water and air.
    • When rays of light of a single wavelength strike a raindrop at different points, scattering is primarily determined by the angles at which they enter the droplet.
    • The interaction between refraction and chromatic dispersion gives rise to the appearance of rainbow colours when parallel white light rays strike various points on the surface of a raindrop.