rainbow is an optical effect produced by illuminated droplets of water. Rainbows are caused by reflectionrefraction and dispersion of light in individual droplets and results in the appearance of an arc of spectral colours.

  • Rainbows only appear when weather conditions are ideal and an observer is in the right place at the right time.
  • Waterfalls, lawn sprinklers and other things that produce water droplets can produce a rainbow.
  • A rainbow is formed from millions of individual droplets each of which reflects and refracts a tiny coloured image of the sun towards the observer.
  • It is the dispersion of light as refraction takes place that produces the rainbow colours seen by an observer.
  • If the sun is behind an observer then the rainbow will appear in front of them.
  • When a rainbow is produced by sunlight, the angles between the sun, each droplet and the observer determine which ones will form part of a rainbow and which colour each will produce.
  • Rainbows always form arcs around a centre point (anti-solar point) because each colour is at a different angle to an observer.
  • The axis of a rainbow is an imaginary line drawn between the light source and observer during the period the bow is visible. The anti-solar point is on the same axis.
  • If you can see your own shadow and a rainbow at the same time then the anti-solar point, the centre of the rainbow, is aligned with the shadow of your head.
  • Seen from the air a rainbow can appear as a complete circle. It is only because the ground around the observer gets in the way that a rainbow produced by sunlight is reduced from a circle to a semi-circle or an arc.
  • The sky inside a rainbow is brighter than on the outside because raindrops direct light there too.
  • When a single rainbow is observed then red will appear on the outside, followed by orange, yellow, green, blue, with violet on the inside.
  • When a double rainbow is observed then the secondary rainbow will be outside the first, it will be less intense, and the colours will be in the reverse order with violet on the outside.