H

Have you ever witnessed the elusive “green flash”? If not, don’t lose hope. I have only seen this rare weather occurrence three times, the most recent being just a few days ago. Like many fleeting moments in nature, chasing after them often leads to disappointment. The green flash is not exempt from this.

I was reminded of my encounters with it, both here and on top of Mowing Word in Pembroke, through reading Kai Bird’s monumental biography of the great atomic physicist Robert Oppenheimer recently. The author describes Oppenheimer inviting a companion one brilliant sunset to take a walk at Cruz Bay in the US Virgin Islands:

“After the sun had disappeared below the horizon, they caught sight of a burst of green light. Robert calmly clarified the scientific explanation behind their observation… the layers within Earth’s atmosphere act as a prism, resulting in a temporary glimmer of green.”

You won’t encounter one every time you search. You need to be aware of where to look. Two of my three sightings have occurred in this area, the exposed white cliffs and brown heather above South Stack cafe on Anglesey. As the sun was setting, the top surface momentarily transformed into a vivid green. Then came the exciting part! A powerful light streaked across the sky.

The atmosphere creates an optical illusion by bending sunlight, separating it into the different colors that make it up. The colors with shorter wavelengths, such as blue and violet, bend more than longer wavelengths like yellow, orange, and red, which are instead absorbed by the atmosphere. This leaves green light, which has a medium wavelength, as the most visible color when the sun is just below the horizon.

The phenomenon known as the “green flash” was first witnessed by me during a climb on the sea-cliffs in the 1960s. A German climber, Reinhard Karl, who climbed with me, also saw it. Unfortunately, he passed away in 1982 in an ice avalanche on Cho Oyu. As I looked out to the sea, a lingering ray of sunlight suddenly formed into a bright green streak of light. It approached me straight on, and then brushed off my shoulder and disappeared into the distance. It was both beautiful and unsettling. To make sense of it, I turned to the words of the father of the atomic bomb.

Source: theguardian.com