Archway to the Light

Some fun facts about rainbows include:

• Each person sees a different rainbow.
• The shadow of your head is at the center of the rainbow.
• You can often see your shadow very far away and at the center of a rainbow.
• The primary rainbow is seen at a 42-degree angular radius from the shadow of your head.
• The secondary rainbow is seen at a 51-degree angular radius.
• The light forming the secondary rainbow reflects twice inside the raindrop, the light for the primary only reflects once inside the raindrop.  This is why the order of colors in the secondary bow is reversed from the primary bow.
• The primary rainbow and secondary rainbows are formed from raindrops located in different areas of the sky.
• The rays that form the primary rainbow that we see are those rays that hit the top part of the raindrop.
• The rays that form the secondary rainbow that we see are rays that hit the lower part of raindrops, which are different from the raindrops that form the primary bow.
• The dark band between the primary and secondary bow is due to total internal reflection of light that cannot exit the raindrop at angles between 42-degrees and 51-degrees.  This is referred to as “Alexander’s Dark Band”, after Alexander of Aphrodisias, who first described the effect in 200 AD.
• Rainbows do not exist in a particular location, they are angular phenomena, not a spatial one.  A rainbow created by water droplets very close to you will look the same as a rainbow formed from the distant rain.  Sorry, there is no “end of the rainbow” at a particular place.

Afternoons, when the sun is low, are usually the best times to see rainbows.  In order to see a rainbow, you need to be located between a rain shower and the sun.  The sun needs to be direct, not diffused by clouds. Learn more here about the correct angles to see rainbows.