Cumberland Falls, along the Cumberland River in southeastern Kentucky, is 13 miles off the main highway—hidden, preserved, and, most importantly for my visit, completely dark. I'd taken the two-hour journey to Cumberland Falls State Resort Park to see one of nature's celestial wonders—a moonbow. It was 12:05 a.m. when I arrived, and the park was overflowing with hurried photographers and children clutching glow sticks. The fanfare was a hopeful sign that tonight, after six failed attempts, I would finally get to see one.

A moonbow, or lunar rainbow, is an extremely rare phenomenon that occurs when moonlight is refracted through water droplets, creating a rainbow much like one formed by sunlight. Under a camera, it reveals its full spectrum of colors, but to the naked eye, it appears as a glistening white arch of light. “I call it a ghost rainbow,” said Jehan Abuzour, a park naturalist at Cumberland Falls.

The description is apt: The moonbow's iridescent glow seems otherworldly, and if you’re like me, the allure of such beauty is irresistible. On this muggy night last July, after a two-year-long pursuit, I finally saw it—a radiant band of silver light spilling from mist-shrouded falls as if summoned by magic. Its ethereal sight was everything I could have hoped for. 

The uniqueness of Cumberland Falls 

Cumberland Falls remains, in a general sense, understated. Its moonbow doesn’t cascade from the grandiose granite cliffs of Yosemite or glisten from Hawai'i’s verdant tropical landscape. Instead, it’s tucked within a rural state like an unsung hero, offering its own beauty to those willing to travel. “I’ve had people come from all over the world—including China, Mexico, and countries in Europe—just to see the moonbow.… It’s really special that we have it here in Kentucky,” said Abuzour. For moonbows to emerge, conditions need to be perfect: a clear, cloudless night, a full moon low in the sky, the right amount of water droplets in the atmosphere (produced by either rain or the spray of a waterfall), and the correct geometry of the moon’s position.

Though moonbows can occur in several places, Cumberland Falls is one of only two locations in the world where they consistently appear (the second being Victoria Falls on the border of Zimbabwe and Zambia), thanks to its precise geographical location. The waterfall’s topographic placement and axis point create the exact slant necessary for the moonbow to appear on cue each month. “Our location gives us the right angle to the horizon in order for the moon’s light to be refracted,” explained Abuzour. “The lunar light must hit the falls at a 42-degree angle and be reflected back through the mist. It’s visible because the viewer is standing right between the moonlight and the falls.”

The interplay between light and water is what makes Cumberland Falls, dubbed the “Niagara of the South,” a perfect stage for the moonbow to appear. Gushing 3,600 cubic feet of water every second over its sandstone edge, the falls rise 68 feet tall and span 125 feet wide and generate a year-round mist, essential for projecting the moonbow’s color prism. 

How to see the moonbow

I know now that my countless unsuccessful moonbow sightings are due to my naive assumption that I could just show up at the park on a full moon and find it waiting for me as if it had nothing better to do than offer a private showing. While the weather can’t be controlled, I’ve since learned there are ways to maximize your chances: The right conditions, timing, and patience are key.

Your chances of seeing a moonbow occur within a five-day window during the full moon phase when the moon is at its brightest. The third day is the optimal time to see it. Abuzour recommended staying more than one night to maximize your chances. “Stay at least two nights if you can. If you really want to see it, stay all five during the best viewing window.” The park does book up quickly, especially in the summer. So, if you’re planning accommodations nearby, do so in advance. However, Abuzour’s favorite time for viewing is during the winter. “The best time to see a moonbow, in my opinion, is February. But all the winter months, in general, are great. The sky is usually clear, the air is drier, and it's not as busy as a travel time.”

Above all, you need patience. “I’ve seen the clouds break, and then all of a sudden, the moonbow appears, even for a brief moment. Just like that,” said Abuzour, swishing her hand. “Just wait; it’s there.”

You could technically see a moonbow anywhere with enough water vapor and the right conditions, but waterfalls strong enough to generate mist are the most reliable. Choose a spot without trees or obstacles between the waterfall and the moon, making sure the mist is on the opposite side of the moon’s position in the sky. The sky must be fully dark and free from light pollution. The moonbow will form when the full moon is at its lowest and brightest point, ideally one to two hours after sunset.

Schedule down to a science

The times when moonbows are visible vary greatly depending on the time of year and when the moon rises and sets. In the winter, the moonbow could be visible as early as 5:30 p.m., whereas in the summer, it can be as late as 3:30 a.m. “I calculate the dates and times using my moonrise calculator, then I add two hours, which is the amount of time it takes to rise above the mountain ridge. At that time, there’s a two-hour window when you can definitely see it,” stated Abuzour.

On the other side of the country, nature photographer Brian Hawkins used a 3D model of Yosemite Valley to create his own viewing schedule for the moonbow that occurs at Yosemite Falls—typically visible in April, May, and June. “I took a graphical approach.… If the light’s behind you and you make a 42-degree arc from where it's coming from, you can figure out where the moonbow will appear.”

Though moonbows look white, the full spectrum of colors are present—but because moonlight is dimmer than sunlight, human eyes have trouble picking up the various colors. To capture the moonbow, Hawkins recommends exposure settings of 15 seconds, at f/4, at ISO 1600 (with more photography tips available on his website). If you’re a novice photographer, any recent model smartphone will do. 

“It's getting easier nowadays because smartphones can actually catch [the moonbow]. Before, you'd have to have a full DSLR camera with a tripod and nighttime [photography] skills,” Hawkins added. What has always made the moonbow so special is its rarity, but even more so, its fleeting existence.

“The [Cumberland] moonbow won't technically last forever,” said Abuzour. She noted that the falls once roared 40 miles downstream, but erosion over millennia shifted their position, and to this day, they’re still moving slowly. “For now, though,” Abuzour reassured, “we get to live today and enjoy the moonbow in our lifetime.”

You can catch the next Cumberland Falls moonbow on January 11, but the best day will likely be January 13. For a complete list of moonbow 2025 dates, check out the schedule here.