The Red Flash

You surely ever heard of the famous rare green flash:


Source

...or of the more rare blue flash:


Source

....that can even be purple under certain conditions:



...but what about the red flash?


An image from Buenos Aires, Argentina by Luis Argerich (photography). The rising sun is miraged into a classical 'Etruscan Vase' or 'Omega' shape. The junction of the two sun images (one rising the other descending) is a vivid red - a red flash, the exact counterpart of the subsequent green flash

Etruscan Vase sunsets and sunrises are mirages of two suns. Let’s talk here only of sunsets – sunrises are the same but with opposite vertical movements. Warm air beneath cooler refracts sunlight to give an upper erect image and a lower inverted image. During a sunset the lower image rises as the upper one sinks.

Interesting things happen where the two images meet. This is at the ‘fold line’.. At the fold the images are stretched vertically. We can see that as the sunset progresses – the two images are liquid-like in that they distort and then join as though attracted and glued.

The high vertical magnification at the fold is the key to the green flash. This is the place of maximum colour dispersion. At the final phase of the sunset, the two images of the sun’s upper limb slide together – the top image sinking and the bottom inverted one rising. Colour dispersion gives the upper limb a slight green rim and as the two images merge the thin green line is all there is. The mirage magnifies the rim vertically – enough to flash out a vivid green.

And earlier in a sunset when the two – red edged - images of the sun’s lower limb meet at the fold? The enhanced vertical colour dispersion then gives a red flash.

The fold line is slightly above the horizon as are the green and red flashes.

Source: OPOD


Fort Stevens State Park, Oregon

Source

I always find these phenomena astounding, but even more so because when the sun sets, and you see it dip below the horizon, you are actually seeing a mirage. By the time one watches a sunset, the light one sees is infact being bent by the atmosphere, so the light continues to reach the eye, despite the fact that the sun is actually already out of direct line of sight.

Sometimes I find myself capable of grasping enormous concepts like black holes, dark matter, star birth and the structure of the known universe, with both hands, and am utterly comfortable with the basic premise that I am dealing with at the time. And then you really sit and think about the insanity of physics which allows, not only the clockwork of the solar system, but the unrelenting glory of little, near magical moments like these to happen.