Make rainbows!

Print Friendly
Make a rainbow
Rainbows are one of the wonders of the natural world: But why do you sometimes see one rainbow, and other times a double? Why do you always see rainbows with your back to the sun? How do they really work? Operate your own rainbow, then find out!
You must use an up-to-date browser version to view this!
Primary   Secondary          Rain Curtain       Single Drop       Multi-drop       
  • Primary checkbox enables the primary bow and its light rays.
  • Secondary checkbox enables the secondary bow and its light rays. Notice this bow is seen from different places on the ground; some observers can see a primary, but not a secondary, or vice versa. Lucky people can see both rainbows.
  • To see both ‘bows (but no light rays), uncheck both rainbow boxes in Rain Curtain Mode.
  • Rain Curtain mode shows two parallel light rays (beams) from the sun refracting off a raindrop at the both the top and bottom of the rain curtain. Outgoing beams show where the rainbow is visible.
  • Multi-drop mode mode shows three parallel light rays refracting off three raindrops at different altitudes. The color you see depends on the angle of refraction.
  • Single-drop mode mode shows the path inside a single drop. Change from primary to secondary to see how the light takes a different path for each rainbow. A secondary rainbow is reflected twice, so it’s dimmer.

Note that primary or secondary bows may be used with each mode.

  • Drag the sun around (across the top and up/down the right side) to change the angle of the parallel light rays from the sun and simulate a time-of-day.
  • Drag the person back and forth to see the effect of observer distance from the rain.
  • When in “multi-drop mode” drag the refracting drops up and down.

This applet is Copyright © 2008, 2011 and 2013 by Tom Whittaker.