HELENA — A rainbow is a meteorological phenomenon that is caused by reflection, refraction and dispersion of sunlight in water droplets.
In order to see a rainbow, the sun will always have to be at your back or at least in the opposite section of sky from the rainbow. We've all seen rainbows, even some double, triple, and even twinned rainbows. But most rainbows are fleeting, here one moment and gone the next.
However, last week's rainbow in Helena persisted all day long. A rare December rainbow that seemingly stuck in the sky for many to see.
There was a very unique set of conditions that led to these colors lighting up the sky for hours. Remember the ingredients; sun, raindrops, and the proper positioning.
On that day rain was falling most of the day, especially up on the Continental Divide. The wind was very strong, which was blowing raindrops nearly 10 miles from the base of the clouds on the divide.
As clouds tend to do, they dissipated with a downslope flow on the east side of the divide. There hardly were any clouds over or near this rainbow, with clear skies above it. Clouds dissipating also allowed the sun to continuously shine into the windswept raindrops, creating a rainbow for hours.