Optical Antics at Sunset

My lovely and talented wife has a habit of being in the right place at the right time to capture nature doing interesting things. This particular shot was taken by cell phone from a moving vehicle in Northern California last night and shows something I’ve never seen before.

Those of you looking for the elusive “green flash” at sunset might never have considered that you can also get the full spectrum of colors too.

This is looking into the sunset, and isn’t your typical rainbow where the sun is illuminating from behind at sunset, such as this one from NASA APOD.


Note: depending on your computer monitor and its settings, you may or may not be able to make out the spectrum. Some adjustment might be needed. What works best for Internet browsing isn’t the best for photos.

Ice crystals in the atmosphere is what I think is the most likely explanation, making a circumhorizontal arc, which is an optical phenomenon. Basically it is an ice-halo formed by plate-shaped ice crystals in high level cirrus clouds. In the photo above, only part of the arc is visible.

An example:

Circumhorizontal arc in relation to 22° halo or circumscribed halo, Oregon –  Image: Wikipedia



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Jim Cripwell
December 19, 2013 10:53 am

When you get the full halo, there are two false suns horizontally. These are called sun dogs.

Mario Lento
December 19, 2013 10:53 am


Jeff in Calgary
December 19, 2013 11:05 am

While I have never seen this in a sunset, it is a commone occurance during the day time up here in Alberta in the winter.
Very cool (or cold?)

Gary Pearse
December 19, 2013 11:06 am

Timely shot and I can see the spectrum – seems rather thick color layers. One of the most beautiful sightings of a standard rainbow for me was when flying in a helicopter doing geolgical fieldwork in a sunshower and seeing two bright and sharp concentric rainbows in complete circles (raincircles?) with the shadow of the helicopter a speck on the ground in the center.

Jenn Oates
December 19, 2013 11:10 am

Dang, missed it entirely!

Jason Calley
December 19, 2013 11:16 am

@ Jim Cripwell Here in NE Florida where I live, sundogs are very common. I see them every week or two. Oddly, most people I have spoken to about them, have simply never noticed. I know local residents nearing retirement age who tell me, “Gosh! I’ve never seen that before!” when I point them out. Makes one wonder how many marvels we humans pass each day and never notice.

December 19, 2013 11:17 am

Not only the Sun but the recent Full Moon also

December 19, 2013 11:17 am

I think Scientific American ran a story in the recent 5 years on the phenomenon of the spherical or 360 degree “rainbow.” The phenomenon is not the same optics as the typical rainbow.
One of the few SciAm articles in the last several years that was not thinly veiled PC stuff.

December 19, 2013 11:20 am

This Summer in July this is the July not now when they are commoin

December 19, 2013 11:24 am


Ian Cooper
December 19, 2013 11:26 am

Anthony, what you have is known as a ‘corona,’ a full spectrum double set of of tight halos around the sun, usually seen at altitude. Your wife’s shot is a very rare example of one on the horizon.
To get a CHA the sun has to be at an altitude of 56 degrees or more. On our side of the ‘Big Pond’ aka The Pacific down here on the SW side CHA’s can only occur between October & February. I’m guessing that on your side it would be April to August and maybe a little longer depending upon your latitude, i.e. the closer to the equator the more time the sun spends above 56 degrees in altitiude.
In the end you are correct in that your wife does have the knack of capturing such rare events, well done.

December 19, 2013 11:36 am

I have seen the green flash 5 times, 4 times at sea and once standing on the beach in Curacao.
Until I saw it for the first time I thought it was just one of those wind-up things for first trippers, like long stands, or buckets of steam to prime the windlass.

Lance Wallace
December 19, 2013 11:37 am

Although an astrophysicist by training, and even teaching astronomy and physics and running a small observatory in the MidWest, I have never seen the “green flash”. Last year, visiting with family in San Diego, we went to the Green Flash restaurant, so named because it looks out on an unobstructed view of the Pacific where one might be able to see the phenomenon. http://greenflashrestaurant.com/
After explaining to the family the general idea of the green flash, I watched carefully with them as the sun sank to the horizon. Suddenly they all exclaimed “There it is!” I was the only one who didn’t see it, apparently having blinked at the crucial moment.

December 19, 2013 11:37 am

Those so called sun dogs or rings around the sun are common.
This is a specific phenomenon and ONLY one that lasts (usually) a few seconds.
I think everyone seen a halo effect around the sun on a day with some fog, or even light rain. And many seen a rainbow.
NONE of the above mentioned effects are the SAME as the green flash that lasts only a few seconds. Until reading the links here – never heard of this effect.

December 19, 2013 11:37 am

Dash it, pressed the post button too soon.
I have no idea what causes the green flash but it is one of the things you never forget once you have seen it.

Mark Bofill
December 19, 2013 11:42 am

But I thought…

“Ever gazed upon the green flash, Master Gibbs?”
“I reckon I seen my fair share. Happens on rare occasion. The last glimpse of sunset, a green flash shoots up into the sky. Some go their whole lives without ever seeing it. Some claim to have seen it who ain’t. And some say—”
“It signals when a soul comes back to this world from the dead!”

Next you’ll be telling me gamma rays don’t actually turn people into hulking green superheroes.
/sarc? /silly.

John F. Hultquist
December 19, 2013 11:43 am

Very nice; thank her for us.
We chased the end of rainbow a few weeks back. Darn Leprechauns kept moving it and we never got the pot of gold.
TheLastDemocrat must have missed the statement from the spouse of the photographer:
This is looking into the sunset, and isn’t your typical rainbow where the sun is illuminating from behind at sunset, . . .

December 19, 2013 12:11 pm

A friend of mine has a few photos from many years ago, when he lived in the tropics and caught many such strange phenomena on film. IIRC the most of them he saw was in West Africa at the end of the summer dry season.
Like your picture, they are a strange sight. I unfortunately have only seen photos of them.

Joseph Haselby
December 19, 2013 12:26 pm

I’m a former Pan Am pilot having crossed oceans hundreds of times. Every sunset I looked for the green flash , saw it only twice.

Henry Galt.
December 19, 2013 12:32 pm

I used to fly from Gibraltar to the UK and twice saw the entire sky as one giant spectrum. Both times due to French air traffic control’s industrial action necessitating a different flight path to the norm.
Beautiful seems such an inadequate word sometimes.

December 19, 2013 12:39 pm

Anthony, your wife shot a beautiful picture of a rare optic phenomenon due to the sunset and the far mountains who shield the sun. This so called corona most happened with the sun (much) higher in the sky. Details of this and many others atmospheric optics you can find on http://atoptics.co.uk/droplets/corona.htm

December 19, 2013 12:44 pm

While serving as a bilge swab on a commercial fishing trawler back in the summer of 1981 I occassionally had the opportunity to come up on deck and breath fresh air for a short time. One evening I was resting against the checkers, gazing out at the sunset, when just as the sun went below the horizon (there was nothing but water between me and Japan) I witnessed a green glimmer, then a full on flash. I saw it only once more after that but feel fortunate for having seen it with my own eyes. Unfortunately I did not have a camera along with me. Even had I brought one it would have been confiscated by the skipper and used to barter for more slaves.

December 19, 2013 12:49 pm

Having lived in San Diego and at the beach for most of my life, I can say I have seen the green flash many times. The thing I have noticed is that it has to be a perfectly clear day with absolutely no haze. The best conditions have been, in my experience, cold (<60F….yes that is cold in SD…), dry (<30% Humidity….again this is considered dry in SD..) and calm. I always wondered if the flash was actually the sunlight refracting through the ocean at just the right angle, since it happens just as the last bit of orange disappears below the horizon.

gopal panicker
December 19, 2013 2:06 pm

I have watched hundreds of sunsets…no green flash.

The Ol' Seadog.
December 19, 2013 2:42 pm

The rarest type is the Complex Solar Halo. In 1962, I saw one in the S. Atlantic, whilst on Passage to Capetown.. Here are some examples.http://epod.usra.edu/blog/2013/02/halo-complex-above-hanover-germany.html http://adsabs.harvard.edu/full/1925JRASC..19..115C (See diagram)
gopal panicker – Green flashes occur at sea and are quite common. They occur when the sea is flat calm.

December 19, 2013 2:48 pm

Global Warming causes unprecedented sunsets!
We’re doomed!

Steve from Rockwood
December 19, 2013 2:49 pm

I saw the Green Flash once. Wondered why a guy goes running around in his underwear at sunset.

O. Olson
December 19, 2013 2:52 pm

I’ve never seen the green flash up here on the Canadian prairies either, But I did see this… one evening we were thrashing wheat, dad on the combine and I was hauling 6 miles home. I pulled out onto the road heading north and noticed something didn’t seem right. It took a few seconds to realize the whole sky to the northwest was greenish. Over just a few seconds the sky got even greener, then faded back to a pink. The sun had just set in the northwest. I’ve always thought this had to have been something related to the green flash but of course a little different. Anyone else seen this? Oh yes, if I remember right, there wasn’t a single cloud in the sky.

December 19, 2013 3:09 pm

I’ve only ever seen partial solar halos in the UK but we do get some very nice lunar halos from time to time.

O. Olson
December 19, 2013 3:34 pm

One more thought, the green sky over several seconds at sunset I described above happened over west central Saskatchewan in late August or early September. It was great thrashing weather, warm and dry, no wind and no clouds. Lots of outfits were out (more but smaller combines back then) and there would have been lots of dust hanging in the air. Maybe that played a part?

Chris Clark
December 19, 2013 4:31 pm

After a bit of playing with hue and gamma settings to show the colours I agree with the ‘corona’ identification. Minnaert in ‘Light and Colour in the Outdoors’ explains it as diffraction from water drops in the clouds.

Janice Moore
December 19, 2013 6:22 pm

Green flashes may be “common.” I, having watched many, many sunsets over Puget Sound or the Pacific Ocean have never seen one — until this evening, long after sunset, here, on WUWT!
Thank you! And, Anthony, please tell your wife “THANK YOU” from us for all the support she has given you over the years, the invisible, but strong, “wind beneath your wings.” But for her, you would not likely have flown as high nor so far… . And your (and Christopher, Lord Monckton’s) soaring to the heights you have has rallied the valiant but scattered warriors for truth making the difference between an enemy drooling in triumph over a cowering, tricked and utterly ignorant, public and an enemy held at bay, snarling and bellowing, unable to prevail.
And they NEVER shall. For, in the end, truth wins.

December 19, 2013 6:28 pm

As others have pointed out, this is a corona. Compare it with the pollen corona serendipitously featured just a few articles articles earlier. Probably the premier website for atmospheric optics is Les Cowley”s http://www.atoptics.co.uk

Berényi Péter
December 19, 2013 6:31 pm

Just for reference.

December 19, 2013 7:22 pm

Um, where’s the green (takeoff on Where’s the beef?) … R-G color vision deficient here …

December 19, 2013 7:40 pm

Anthony, please thank your wife for great timing with the camera, a very nice photo indeed.
These optical effects fall into three categories; scattering, diffraction and refraction/reflection. What causes each optical effect (illusion, mirage, chimera) is determined by the size of the particles involved relative to the wavelength of light.
Scattering is what causes the sky to appear blue when observed from the surface. The “particles” are actually the gas molecules (N and O2) which are smaller than the wavelength of light. This Rayleigh scattering sends the blue light off in all directions and you observe an indistinct blue diffuse surface.
Another case of scattering, Mie scattering, occurs with larger particles (dust, smog, etc.) This occurs in longer wavelengths (reds and greens) and causes the red glow at sunset. Again the scattering is “all directional” so there is no distinct structure to what is observed.
Diffraction is caused when the particles are about equal to a wavelength or so of the light. This is what causes the “halo’s” around light sources when ice crystals or snowflakes are present between the observer and the light source. This “bends” the light by a fixed angle which depends on the wavelength. Since the “bending” is more limited in distribution angle a more distinct (but not focused) ring or arc is observed. “fogbows” are colored rings around light sources visible when the fog is between the source and the observer. The fog has smaller physical particle size than water droplets.
The last case is the rainbow, in this case the water droplets actually refract/reflect the light backwards towards the observer; light behind the observer, water droplets in front of the observer, rainbow visible by observer. The front (closest to the observer) surface of the water droplet refracts (bends) the light into the droplet. Since the refractive index of the water varies with wavelength this bend has a different angle for each color. Then the back of the water droplet reflects the light back towards the observer. This results in the rainbow, which is ironically enough an example of “back radiation” (sorry, I could not resist, but it is true).
There are optical design software tools (for example “Zemax” (a registered trademark) and others) which are capable of modeling these effects. The models are based on the basic rules of scattering, diffraction, and refraction and include measurable physical characteristics of the materials involved. For example, the refractive index of water can be easily measured at different wavelengths. A simple model of the Sun (including color spectrum based on blackbody temperature) striking a sphere of water (modeled with the wavelength dependent refractive index) will yield a nice “model” of a rainbow, including the “arc” (which is mostly a function of the source (sun) to observer angular relationship).
The “green flash” is caused when the light from the setting sun actually enters the surface of the water and then leaves again on its way to the observer’s location. Of course the angles where this can happen are very small and as the Sun “sets” they only occur for a brief period. Any rough seas or humidity will blur the green light so it cannot be seen distinctly.
Cheers, Kevin.

December 19, 2013 9:22 pm

Any green color in the sky more than a few percent of 1 degree from the sun is not the green flash. The green flash is a flash of green at the top edge of the setting sun. It is caused by a prism effect of the Earth’s atmosphere. It generally occurs when the sun is partially below the horizon, usually majority below the horizon, and the air that the sunlight goes through is so clean that the main sunlight is orange rather than red. If the sun appears a yellowish shade of orange when is is partially below the horizon, especially halfway below the horizon, chances of seeing the green flash are better.
Some spectacular green flashes occur just as the sun visibly completely sinks below the horizon, except for the top edge’s green light spectral component that persists for a brief time after the yellow, orange, and red main light of the sun sink below the horizon. In some cases, one may see the green flash changing from a yellowish shade of green to a less-yellowish shade of green.
In extreme cases with extremely clean air, the green flash changes to blue-green, and is called the blue flash. That probably requires air so clean that the sun is mostly a noticeably yellowish orange, maybe almost a flamelike very slightly whitish yellow, when a majority of it is below the horizon – which I have never seen.
If conditions appear good for a green flash, it is a good idea to take a video or a series of rapid-fire still photos with a camera set at a high zoom setting, and exposure low enough for the sun to show as roughly candle flame to incandescent lightbulb to possibly banana edible part color. You probably want the main part of the sun overexposed, but not to cream color or white. If the green flash occurs before the sun is 99-plus-% below the horizon, the human eye can miss it, while a camera may catch it.

December 19, 2013 9:54 pm

Thanks, Anthony, your wife has a remarkable talent!
I learned about sun-dogs, halos, green flashes etc. from Prof. Jim Kaler of Univ of Illinois-Urbana, 1973-4. He admonished us undergrads to always check the sun each day, and thanks to him, I’ve seen all sorts of halos and other light phenomena. I DO recall how the entire class sniggered when he mentioned the “green flash”!
Please see some of his photography at his website. He’s a remarkable guy, we are still in touch by email! http://stars.astro.illinois.edu/

Larry Ledwick
December 19, 2013 10:36 pm

I’ve seen a green flash one time in the late 1960’s. I was at the University of Colorado and out walking between buildings just as the sun rise broke over the horizon. I was looking up at the flatirons above boulder just as the first rays of the sun illuminated them, and very briefly they were a distinct green color before they took on the expected warm orange of the rising sun.
Another solar optical illusion I had the privileged of seeing was a sun pillar.
The blizzard of 1982 which shut down the city of Denver on Christmas Eve buried the city under 2 or more feet of blowing snow. In some places it drifted 3-4 or more feet deep. The local hospitals put out a call for owners of 4×4 vehicles to help them get their nursing staff home and bring in new personnel after the storm broke. I went down to Lutheran hospital in west Denver and picked up 4 nurses and proceeded to try to get them safely home. In Arvada I had one nurse who lived on a steep hill on a street which was drifted 3-4 ft deep with all the cars buried to mid side windows. The snow was unbroken all the way to the bottom of the hill. After considering my options, I told her I would drive all the way to the bottom of the hill breaking the trail then turn around and bring her back up to her house. I was in a full sized Jeep Cherokee and the snow was head light deep as we went down the hill. I blew down the hill at a good clip because I was afraid if I stopped I would not be able to get going again, so we were throwing a good “bow wave” of snow as I pushed through the deep snow. I got turned around at the bottom and brought her back up to mid hill and after some considerable effort, she forced the passenger side door open enough to squeeze out and wade hip deep through the deep snow to her front porch.
After dropping her off I went to drop off the last nurse in Westminster and turned onto 92nd ave east bound from Federal just as the sun came up. This is a local high spot with a fantastic view of the entire Denver basin and a clear view all the way to the eastern horizon.
Due to the previous nights blizzard, the atmosphere was filled with invisible uncountable trillions of microscopic ice crystals and just as the sun broke the horizon it was like a powerful spot light was turned on pointing vertically from the location of the sun and a brief but brilliant pillar of light shot up from the sun.
It was a dazzling display that unfortunately only lasted a few seconds as we drove down the road and our position moved out of the ideal viewing angle for that light show.

December 19, 2013 11:46 pm

People interested in this sort of thing might like “Rainbows, Halos, and Glories” by Robert Greenler.

Leo Smith
December 20, 2013 2:16 am

for a green flash you need to stare directly at a setting tropical sun as it dips below the sky goes dark except for a green after image burned in your retina. As the video above shows its not ‘really there’. I tried the same trick with a still camera: no green flash ;(

Ed Zuiderwijk
December 20, 2013 5:42 am

“Ligt and Colour in the outdoors” by Minneart with photographs from a Finnish bloke has a full chapter devoted to it.
The green flash is not an “after burn” image, that would be black! And you don’t need the sun set or sun rise. What you do need is a low very sharply defined edge behind which the Sun disappears or from behind it appears. The horizon without clouds at sea would do, but you need exceptional transparency as well.
I personally saw (with several others) the green flash when the Sun appeared from behind distant clouds over Tenerife as seen from the top of La Palma island.

December 20, 2013 5:51 am

Concerning sundogs, a few years ago I saw no less than 5, a large halo round the sun and four similarly sized halos at 90 deg and touching each other and the central halo.

Mickey Reno
December 20, 2013 7:26 am

I’ve lived along the beach in Western Mexico, and now on a sailboat. I’ve never seen a green flash, but know many people who say they have. I’ve know some who ‘saw’ it as I was looking at the same sky and saw nothing. But people are different. Some are color blind, and some have extra color detection, called tetrachromats.
There is also the possibility that psychological suggestion makes some people see what they expect to see. We call these people climate scientists.

Weather Dave
December 20, 2013 9:12 am

On our cruising yacht, this last season in New Caledonia the Green Flash was a regular occurrence. You need a lack of low cloud at sunset. It’s best seen with a pair of binoculars; do not look thru the binoculars until the last fraction of the Sun is visible or you will damage your eyes.

December 20, 2013 12:57 pm

Despite years of looking for the green flash, I never managed to see or photograph one until about 2 weeks ago when I stopped to look at the sunset as I drove home along the Scottish west coast:
Another tick on my bucket list.

December 22, 2013 11:17 am

Anthony says: “Ice crystals in the atmosphere is what I think is the most likely explanation”
I agree, this is a very nice shot for being took with a camera phone. The reason why I agree is because, when I’m out at night observing the night sky, over the past few years I’ve noticed a large increase in the amount of Moonbows I would see during a moonlit sky, they were so rare to see before 2008 where I live, and they were usually faint (possibly caused by water droplets), now they are more frequent, very pronounced and bright, this type of Moonbow seem to be different in that they are created mostly by Ice crystals in the atmosphere and not just water droplets. I would say that the sunset in the photo and frequent Moonbows occurring now are the Ice crystal variety of this optical effect.

Kevin Kilty
December 22, 2013 1:47 pm

Joseph Haselby says:
December 19, 2013 at 12:26 pm
I’m a former Pan Am pilot having crossed oceans hundreds of times. Every sunset I looked for the green flash , saw it only twice.

Most of us land-locked people have never seen a “green-flash”. I saw one once on the Oregon Coast. It requires a very long distance to the horizon and a suitable temperature versus height structure along the visual path.
Anthony’s picture of the corona was so subtle that I missed it completely at first. It doesn’t look like a green flash, or at least like the one I saw. However, it is quite a nice picture when one sees the subtle colored haloes.

Kevin Kilty
December 22, 2013 1:49 pm

Mickey Reno says:
December 20, 2013 at 7:26 am
I’ve lived along the beach in Western Mexico, and now on a sailboat. I’ve never seen a green flash, but know many people who say they have. I’ve know some who ‘saw’ it as I was looking at the same sky and saw nothing….

It is so brief that people can miss it easily.

Kevin Kilty
December 22, 2013 2:20 pm

O. Olson says:
December 19, 2013 at 2:52 pm
I’ve never seen the green flash up here on the Canadian prairies either, But I did see this… one evening we were thrashing wheat, dad on the combine and I was hauling 6 miles home. I pulled out onto the road heading north and noticed something didn’t seem right. It took a few seconds to realize the whole sky to the northwest was greenish. Over just a few seconds the sky got even greener, then faded back to a pink. The sun had just set in the northwest. I’ve always thought this had to have been something related to the green flash but of course a little different. Anyone else seen this? Oh yes, if I remember right, there wasn’t a single cloud in the sky.

I’ve lived about half my life on western prairies too, and I find the sky opposite the sunset to be as interesting and beautiful as the sunset itself. The color of the sky directly above the indigo shadow of the Earth is generally about the color of the sunset, or at least that is what I have noticed on the northern prairies of the U.S. Thus, your green sky could be related to a green-flash on that occasion, but it could also result from a corona like the one Anthony posted. The confusing issue is always that the eye can often see complementary colors (green being complementary to pink) juxtaposed even when one of the pair isn’t really present. This comes from exhaustion of dyes in the eye’s color receptors. A number of people on this thread have spoken about the green flash being an afterimage of the Sun, and I can see why they might think it so. The Sun’s afterimage lasts a long time and is very complex. I find it evolves from a very bright image that I can’t describe as a color at all through purple and eventually fades as green. But the green flash is unmistakable after a person has seen it once. It doesn’t look like an afterimage or a corona.

December 22, 2013 4:07 pm

Jules Verne wrote a story about the green flash called “The Green Ray”. A couple was standing on a hill waiting for it, but just at the crucial moment their eyes meet and… they miss it! But they realize they are in love, so it all ends happily.

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