St. Patrick's Day and Double Rainbows

March 9, 2017
Double Rainbow in Iowa

It’s time to celebrate being Irish (or pseudo-Irish) and look for that pot of gold waiting for you at the end of the rainbow.

I can’t help you with the Irish gig, but I can discuss rainbows. I can also pass on a Central European secret for how to get to the pot of gold.

This is the season to start seeing rainbows, whether you are in Ireland or Texas. The heated air from the South is expanding north and mixing with the cold air remaining from winter—producing spring storms. The combination of raindrops and sunlight produces the magic of rainbows.
six rainbows

Mix water droplets, sunlight, and you get a rainbow—or, in this case six rainbows. SOURCEThe Astrophysics Science Division of NASA/GFSC Credit Terje O. Nordvik

How Are Rainbows Formed?

As the sunlight pours into the rain, each drop acts as a prism, refracting the light. The white sunlight is broken down into its component colors. The back of the raindrop reflects this series of colors, each at a different angle. You see different colors from different raindrops and it blends into a bow.

Each raindrop acts as a prism Source − Wikipedia.

How Are Double Rainbows Made?

For double rainbows, light entering raindrops refract twice, going in from the air to the water and reflecting back out of the water into the air. Each refraction produces a rainbow. You can frequently see the bright first rainbow with a fainter reverse rainbow on the outside.

Once you know the basic science, you can start to understand why there are so many different crazy rainbows. The more the light bounces around, reflecting and refracting, the more different rainbows you can get. 

There are even multiple rainbows. Rain, mist, reflections and light bouncing through the water droplets creates many different rainbows. One scientist, with a laser, created 200 at once.

Ever heard of monochrome rainbows? Sometimes, at sunrise or sunset, when the blues and greens have faded from the sky, you get a brilliant all-red rainbow.

An un-enhanced photo of a red (monochrome) rainbow. Source − Wikipedia.

Whether there are one or fifty rainbows, they are all beautiful images that retreat as you approach them. The end of the rainbow with its pot of gold always remains tantalizingly out of reach.

But, here’s some hope for St. Patrick’s day. A number of European countries have rainbow folklore, spinning tales of elusive gold. In Silesia, (part of Central Europe) legend says that angels put a pot of gold at the end of the rainbow and only a naked man can reach it.

So fortify yourself with green beer, warn the neighbors, and go for the gold!


About This Blog

Mike Steinberg is Senior Vice President for Special Initiatives at AccuWeather Inc in State College, Pennsylvania. He is also a member of the National Weather Association and the Canadian Meteorological and Oceanographic Society.