Brocken Spectre a rare optical illusion was

Brocken Spectre, a rare optical illusion was spotted on Tamanos Mountain in Washington's Mount Rainier National Park.

On their way down from the summit when Radka Chapin and her fellow hikers came across something that stopped them in their tracks: A rare optical illusion known as the Brocken spectre.

"Well, we’re definitely not leaving now!" Chapin wrote in her report on the discussion forum nwhikers.net. "Over the next few hours, the 'spectre' would show for brief moments before it disappeared with moving clouds."

Several hours later, the hikers continued on their way back when they saw the phenomenon again.

"The spectre became more prominent, colorful, and was projected onto clouds directly below us. It was a breathtaking show," said Chapin.

The phenomenon is commonly seen near The Brocken, the highest peak of the Harz mountain range in Northern Germany, hence the name Brocken spectre. The illusion forms when the sun casts a person's shadow in the mountains, and includes a rainbow halo if there are water droplets in the air.