The Moonbow at Cumberland Falls

In 2013, Kentucky Life featured a segment on one of the state’s natural wonders: the moonbow at Cumberland Falls. Visitors and patient photographers can see this rare occurrence at the falls on clear nights when the moon is full.

“The mist that comes off the falls comes up and the light from the moon filters through and creates the moonbow,” explains Pam Gibson, a park naturalist at Cumberland Falls State Resort Park. “You can’t see colors in it usually until you develop your photograph, but then it has all the colors of a rainbow. The moonbow happens every month, usually for five days if the skies are open.”

Cumberland Falls is the only place in the Western Hemisphere where conditions are right to create a reliable moonbow, also called a lunar rainbow.

“Our falls are not artificially lit,” says Gibson. “We don’t have lights on them in the evening to light them up like they do at Niagara Falls and Yosemite Falls. Victoria Falls lost their moonbow when they had an earthquake. The rocks no longer support the falls in the same way so that when the light is filtered through the mist, it doesn’t light it up as a moonbow any longer.”

Gibson says that visitors need to be patient to get a good moonbow sighting. The best way to catch it? Block out several days around the full moon and enjoy a vacation at the park so that you can visit on several nights when moonbow conditions are likely.

For photographers, capturing the moonbow is an exercise in patience, and it requires the right equipment.

“Your best friend when you’re photographing the moonbow, is a tripod because the exposure to get the image properly could be two, three, or four minutes, depending on the camera,” says photographer Charlie Baglan. “There’s no way to hand-hold a shot for that long.”

Baglan adds that you’ll need to turn the flash off to shoot the nighttime phenomenon; a flash will just illuminate the mist and give you a frame full of fog.

“What I use at the moonbow is usually a digital SLR, always on a tripod, usually really slow shutter speeds,” says KET photographer Steve Shaffer. “The cameras I have, they’re usually pretty sensitive, and I keep the ISO or the film speed at 400 or 640. Usually I can get a 30-second exposure at f-4, 4.5, or 5.6. It will change a little bit from trip to trip, just depending on how bright the moon is. I’ve gotten pretty good results so far.

“This is my fourth or fifth trip down here to see the moonbow,” Shaffer says. “It’s always a pretty cool trip. There are always lots of nice people. There are always people who’ve never seen it before, so it’s really cool to talk to those people.”

This segment is part of Kentucky Life episode #1812, which originally aired on February 23, 2013. It was also included in Kentucky Life episode #2420, celebrating the 50th anniversary of the moon landing. Watch the full episode here.