As a meteorologist, I have long been aware of the Green Flash and would always try see it when I watched the sunset over the ocean. But I never did; and most of the colleagues and friends that I speak to haven’t either! That has all changed since moving to the coast about a year ago. Now that I frequently photograph sunsets, I probably capture it at least 50% of the time! So, what has changed?
The biggest difference is that I switched from trying to “see” the Green Flash to photographing it! When most people are trying to see it, they are staring into a bright yellow-orange-red ball, and in doing so their irises dilate down to the size of pinheads and their color vision is degraded; making it almost impossible to ever see the green flash with the naked eye.
There are actually two different basic types of Green Flash. The first occurs as a relatively bright flash of an emerald-green color right after the upper disk of the sun has dipped below the horizon. This “classic” type is the one most often seen when a person has not been watching the bright sun during the setting process. It’s the result of warm air overlying the colder ocean and the effects of an inferior-mirage display of the sun and the actual disk of the sun interacting. (For a great technical explanation see https://www.atoptics.co.uk/atoptics/gfimform.htm).
The second variety of Green Flash appears as a small detached element of green light above the disk of the sun. During the course of the sun setting, there are often multiple occurrences of these “green wiggles” of light. This type of flash happens when there is a temperature inversion (i.e., cooler air near the surface and warmer aloft) resulting in a mock-mirage. (See https://www.atoptics.co.uk/atoptics/gfmmform.htm)
And as I found out recently, bright light from the full moon can also be the source of a Lunar Green Flash! The image below was taken November 2020 as the full moon set next to Pigeon Point Lighthouse on the San Mateo County, CA, coast. And it wasn’t until I got home and looked at the image on a monitor that I noticed the tiny wiggle of a rare Lunar Green Flash.
For a deeper dive into the topic check out what I consider the two definitive resources that I have found on the topic. The first is Les Cowley’s Atmospheric Optics pages (https://www.atoptics.co.uk/), which is a great go-to source for not only the Green Flash, but also Rainbows, Halos, Rays and dozens of other visual phenomena. The second is Andrew Young’s Green Flash pages (https://aty.sdsu.edu/). Enjoy and happy Green Flash hunting.
Jan Null, CCM
Certified Consulting Meteorologist
Golden Gate Weather Services