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Weather Wise: The Rainbow Connection

Weather Wise: The Rainbow Connection
Posted at 12:59 PM, Mar 26, 2024

HELENA — Rainbows form when sunlight hits a raindrop, there is refraction or bending of the sunlight through the drop. A rainbow always appears in the section of the sky opposite the sun, so the big orange ball needs to be at your back.

Our old friend Roy. G. Biv can remind you of the colors - red, orange, yellow, green, blue, indigo and violet.

Sometimes a double rainbow forms, with the secondary higher rainbow having reversed color, caused by light reflected twice in each raindrop.

A twinned rainbow is extremely rare and appears as two rainbow arcs that split from a single base. Twinned rainbows are caused by a combination of different sizes of water drops falling from the sky.

Rainbows are usually only seen as an arc, or part of a circle because the lower half is usually blocked by the horizon. But the next time you're in a plane or up in a really tall building, you might see a full-circle rainbow.

The highest rainbows are seen just after sunrise or just before sunset when the sun's elevation is at its lowest. Low-arc rainbows form when the sun is at any position between the horizon and 42 degrees above it.

Rainbows need the sun but moonbows use moonlight. These are often harder to see because there is less light, and they are not as bright because of that. Moonbows often look white.

And finally, there are fogbows. I took this picture years ago in Wyoming. Light, water droplets, and refraction of that light cause another faint white arc.