Good news, we have one that happens *fairly* regularly here in Kentucky. You’ve probably heard of the Cumberland Falls Moonbow, but what’s the real story behind it? Let’s find out!
First, a moonbow forms the same way a rainbow forms but uses the sun’s light reflecting off the moon’s surface (moonlight) as the source. The light is reflected and refracted by water droplets in the air and the bow appears. Moonbows form in very specific atmospheric conditions making them pretty rare. The area has to be away from light pollution as the artificial light will obscure the bow. The moon must be low in the sky, but unobstructed by terrain or vegetation features. The moon needs to be full or near full, and there must be water droplets present in the air. The most important thing is, skies must be clear, or clear enough to not block the moonlight.
A moonbow appears mainly white in color to the human eye or has a faint rainbow color, due to the lower level of light reflected by the moon. It takes bright white light to see the entire color spectrum, so most moonbows will be whitish in color or may have a dull rainbow color. Regardless, the sight is amazing. Cooler air can help brighten the colors.
The lunar rainbow at Cumberland falls is one of only two “predictable” moonbows in the world. The best time for viewing is between dusk and about midnight on nights with a full moon along with the two days before and after. The moonbow will be highest, relative to the ground, during moonrise and will “shrink” as the moon continues to rise until it is unobservable. The moonbow at Cumberland Falls has been a popular tourist attraction since and before the area was created as a State Park. It is likely that the Native people of Kentucky viewed this very phenomenon before early European settlers.
At Cumberland Falls, these criteria seem to come into play more often than usual. The 65-foot tall and 125-foot wide (on average) falls is enough to put enough moisture in the air for the moonlight to work with. During a full moon, the odds of seeing the bow go up around the falls.
Conditions were just right for a #moonbow in Cumberland Falls, KY. Light from the full moon refracts through mist from the waterfall creating the bow. Cool air produced the colors, otherwise it would have appeared white like a fogbow!
— AMHQ (@AMHQ) April 30, 2018
Every year, Cumberland Falls State Park puts out a list of dates and times that are best for viewing the moonbow.
While it’s not guaranteed that you see a moonbow, the chances are highest during these dates and times. Of course, the weather has to cooperate and skies must be clear. So, next time you’re looking to go see the moonbow, check the forecast and enjoy one of nature’s many wonders, right here in Kentucky!