The Green Flash, What is it about ???

Have you ever been sitting with friends, watching a beautiful, tropical sunset, when one of them said, ‘I wonder if we will see the green flash tonight?’ You do not know what they are talking about, but you play along and like everyone else you stare at the sun until it is gone. There was no flash, and you think you have been had. Well, you have not. There is a green flash, but you have to be very lucky to see it. The green flash was first documented by Captain Black of the H.M.S. Terror while in the Arctic during its expedition of 1836-1837. Referring to a January 17 event he wrote: ‘In the morning however, at a quarter before ten o’clock while standing on an ice hummock about seventeen feet high, and looking toward the sun I had observed the upper limb of the sun, as it filled a triangular on the ridge of the headland, of the most brilliant emerald color, a phenomenon which I had not witnessed before in these regions.’ At first glimpse of a rising sun or final glimpse of a setting sun is when you might see a momentary burst of dazzling green. To understand this one must begin with the fact that air is a refractive medium, it bends light. Although the bending produced by a given layer is very weak, it becomes progressively stronger as light approaches the Earth’s surface and air density increases. Air is also dispersive – it bends light of different frequencies by different amounts. At sunrise and sunset, when oblique rays from the sun travel a longer distance through the atmosphere, the light reaching the Earth has had a considerable portion of its blue content removed. The scarcity of blue light causes the peak stimulus to shift slightly towards the yellow, making a greenish-yellow flash possible!