 -- Two hikers witnessed a rare occurrence while climbing a mountain in Mount Rainier National Park: their own optical illusion.

Radka Chapin and her husband Chris were standing on the summit ridge of Washington's Tamanos Mountain on Saturday when they got to see an effect known as a “Brocken Spectre.”

A "Brocken Spectre" occurs when a person is standing above the horizon, causing a shadow to be cast on the mist or cloud below. As a result, a circular rainbow halo forms around the shadow or "Spectre."

“We were secretly hoping we would get lucky on Saturday as the conditions looked perfect,” Chapin told ABC News.

She added: "As the day went on, the Spectre would last longer and was more prominent and colorful. The best display was in the evening, when the Spectre appeared very clear, large and a short distance from us, right before thick clouds rolled in and obstructed the sun."

Chapin said she has witnessed other forms of atmospheric phenomenon before but last weekend's Spectre was incredibly significant.

“I have seen many halos in the mountains, beautiful storm clouds, incredible sun rays, but this was my first time seeing the Brocken Spectre,” she said. “It's truly a spectacular sight to see.”