After the past six weeks of exhausting election campaigning and coverage I think Canada deserves a rainbow–a double rainbow to be exact.  Here is a simple experiment I came up with using house-hold items to create your very own double rainbow.  All you need is a bright light source, a clear jar full of water, and a dark room. It can be a tricky at first to see the double rainbow so stick with it. 

Rainbows are usually seen right after a big thunderstorm when the sun is behind you. White light enters the raindrops, bounces around inside, and then is reflected back to the ground. White light is really composed of all the different colours. As the light hits the raindrop, the different colours separate and no longer travel along the same path. Different colours of light leave at different angles.

Inside the raindrops most of the light makes a single bounce and then leaves the raindrops. The light (that is now split into its different colours) forms the primary rainbow that we are used to seeing. Some of the light, however, can continue to bounce around inside the raindrop. This light leaves the raindrop at a different angle forming a second fainter rainbow that appears above the primary rainbow. Because these secondary rainbows are much fainter it is usually only possible to see them when there is a dark background behind them (like black thunder clouds).

Step-by-step instructions

Double rainbow experiment setup

To create a rainbow you need two things: a light source (to act like the sun) and a round glass jar full of water (to act like a water droplet).

  1. Set the lamp up on a chair, table, or high place.  Sit on the ground below the chair–you should be quite a bit lower to see the best rainbow.
  2. Hold the water-filled glass jar in front of you at an angle of ~45 degrees.  Now start to raise the jar higher.  You should see a reflected spot in the jar that looks like a rainbow.
  3. Keep raising the jar and a second spot will appear.  This is the double rainbow.
Double rainbow results

Let me know how it works out.  Special thanks to Jaime Almond who helped me shoot the video as well as Catharine Holloway, Evan Meyer-Scott, and Robert Prevedel for acting like photons.