The Green Flash and the Blue Flash
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The Green Flash is an exceptional , mind-boggling , poorly-understood sight of Sunrise and Sunset . The true and legendary Green Flash seems as bright as a flashbulb and has the same momentarily disturbing effect on vision . It is so rare that I am unaware of any image which captures it . Two preliminary matters : 1) The green segment and the green flash are both remarkable sights . There is a difference between the green segment and the green flash . The green segment is of normal photospheric brightness . The green flash is an immensely brighter burst , seemingly 10 or 100 times brighter . Mathematical nomenclature : A chord cuts off an arc from a circle and , simultaneously , cuts off a segment from a disk . Application : Ideally , a spherical sun rises above a horizontal , linear horizon to expose a segment of itself . Reality : This ideal sun is actually a range of suns of different spectral colors , conventionally , the red sun , the orange sun , the yellow sun , the green sun , the blue sun and the violet sun , although actually , a much larger range , a more or less continuous range is present on various occasions . When near the horizon , these suns are separated by chromatic differential atmospheric refraction . The lowest of these is the red sun and the highest above the horizon is the violet sun . The yellow sun is typically the brightest . The violet sun rises first and sets last , but is almost always dimmed to invisibility by atmospheric aerosols , etc. A segment of the blue sun is occasionally seen . More frequently , a segment of the green sun can be seen at Sunrise/Sunset while the yellow sun is still/already below the horizon . The green segment , it could be called the green glow , or the green shift , is infrequently seen , but not really rare . When the sky near/at the orient/occident is very clear , the green segment can normally be seen . It is an easy inference that , from a very favorable location , the green segment can be seen dozens or hundreds of times per year . The first color seen will vary over pretty much the whole spectrum . Sometimes greenish-yellow , sometimes yellowish-green , or bluish-green , or others . Quite often , as the first bit of the yellow sun rises , the green segment will split into two green pieces separated by a yellow segment . The green segment has been imaged many times . 2) The idealized picture just presented is severely modified by the atmosphere . The shape of the segment(s) is often wildly and greatly distorted . Quite often , as the first bit of the yellow sun rises , the green segment will split into two green patches of some shapes or another at the termini of a yellow bar . Also quite often , the Sun is dimmed to a greater or lesser extent as it rises or sets , just as it is less often when higher in the sky . More reality : Anyone who has expectations of how a Sunrise or Sunset will appear is almost surely bound to be disappointed . The range of phenomena is simply too great . When the Sun is near the horizon , its light takes a long path through the atmosphere . This long path quite commonly facilitates a wide variety of meteorological modifications of the image . The long path also tends to scatter blue light more efficiently ( thus the blue color of the midday sky ) making the image of the Sun , which is formed only from light which survives the trip , redder in color . In particular , violet and blue are frequently seen to be missing altogether . Consequently , there is no such thing as a unitary , or uniform , "green flash" phenomenon , such as you may have read about in less authoritative sources . The green flash is not something you either see or don't see , like some sort of step-function . There are intergrades between the green segment and the much rarer , and much brighter , green flash . Sometimes the green will be much brighter than the usual , maybe a little brighter , maybe much , much brighter . Sometimes as bright as a flashbulb . That's the Green Flash . Any of the entire range of appearances from green segment to green flash is a quite remarkable sight , especially on initial viewing or if unexpected . But , no one who has seen a true and legendary Green Flash could possibly confuse that immensely bright flash with the mere color shift of a green segment . Sometimes , these green phenomena are actually blue , or as a few images suggest , violet . Sometimes , the green segment is detached from the main part of the photosphere , sometimes not . The green segment can be brilliant and striking , truly a remarkable phenomenon , and people who see it may remember it for a long time . "Ordinary" green segments are still definitely brilliant , striking and remarkable . They are not really "ordinary" . But the green flash will "knock your socks off" ; it seems to be as bright as a flashbulb , and momentarily disturbs your vision . It's a flash , a burst , much brighter than the brightness of the unenhanced photosphere . That's why it's called a flash . - - - Notice to imagers and photographers . Please don't throw away your images . I worry that , with such wide distribution of so many mislabeled representations of the green segment , imagers may have thrown away as useless the greatly overexposed images that would document the green flash . This is a highly unfavorable situation . - - - My observations . Although far from ideal , conditions under which I typically observe are quite often good enough to allow me to see the green segment . I've seen the green segment many hundreds of times . My observations reveal a wide range of phenomena which seem well-explained by these basic principles . I wonder , under my typical conditions , if I may not have been advantaged in observing these phenomena by : a) an elevation far above sea level , b) binoculars , c) insomnia , and d) consequent convenience of Sunrise . People who flock to the seashore for its far horizon may be disadvantaging themselves by immersion in the marine murk . I have seen the classically described phenomenon , an extremely bright flash of green light , as "bright as flashbulbs" . Much more frequently , I have seen a bright green glow , lasting a greater or lesser length of time , and assuming a variety of shapes and sizes . More frequently than that , I have seen merely bright green specks , also of various durations , shapes and sizes . The large number of these specks I have seen may be inflated by the preponderance of my observations over a land horizon at Sunrise through binoculars , where it is easy to catch a "first bit" through leaves of trees . Many , many times , there is no green , not really , just yellow , or orange or red ; many of these , of every hue . I generally ignore any dim phenomena at Sunrise , since I can't distinguish them from isolated illuminated clouds . And it is only with experience that I can properly anticipate the pace of events at Sunset and make this distinction then . The blue flash . On extreme occasions , the phenomenon is not green , but blue . I have seen a number of bluish-green and greenish-blue phenomena , of various hues , mostly very green . At the equinoctial Sunrise , 1998 SEP 23 , I saw a BRIGHT BLUE FLASH . In detail : The Sun rose behind trees , which are far away and not of any great consequence . Immediately prior to Sunrise , the whole area of the sky near the orient was especially luminous , so much so that it raised the question "Why is the sky already so bright if the Sun isn't up yet ?" . I saw a definite brightening of the pale orange at the orient . 31.40 seconds after that , at 11h 18m 23.6s UTC (I was too excited to have the patience to obtain the hundredths , personal equation = about .25s not applied) , I saw the "first bit" ; it was bright green , rapidly evolving , giving way to green and yellow spreading out horizontally , and then it happened . A BRIGHT BLUE FLASH , as blue as could be , not more green than violet , occurred 6.26s after the "first bit" and high , not directly in front of the first bit ; but a fraction of a degree higher , and seemingly big , perhaps as big as the , as yet unrevealed , Sun . If the brightness hadn't been so disturbing , I'd call it a lovely blue , a sky blue or a baby blue , mostly a sky blue . After the blue flash , the color continued to evolve , moving left and right , until the green ended 3.24s after the blue flash . I spoke with an experienced and enthusiastic meteorologist , Andre Bernier , who said there was nothing very unusual about the weather at sunrise . He said there was a small inversion of 10 or 15 degrees F for about 200 feet or 1000 feet at the surface . Apparently , the key to seeing blue phenomena is a clear path , which can occur even if there are a few clouds , as there were . As with my 9 observations of the corona of our Sun from within the umbral shadow of the Moon , but to a lesser degree , the words above describing the blue flash are rather definitely insufficient to thoroughly describe the phenomena . There is something very significant missing . You have to be there and see them yourself to really understand . ( And this remains certainly true even if right now you are smugly telling yourself I am surely mistaken in this . It's an observing thing . ) In retrospect , I see that in some ways I did a pretty lame job in reporting the blue flash I observed : "a blue flash is better than a green flash" : http://www.satobs.org/seesat/Aug-1999/0099.html Pressured by the demand of e-mail , hastily improvising , I mistakenly chose a jocular subject header , intended to be light-hearted , which I now see as troublesome , interfering with explaining the message . As Michael Feldman might say , "sticklers for the truth" should substitute the word "rarer" . With hindsight , I wish I had used a title with less potential for confusion , since my dominant purpose was to dispel confusion . And I never quite got around to explaining clearly that the observing experience of a green flash is qualitatively different than that of the green segment . I surmise that favorably situated observers could observe the green segment 100 or 200 times per year or even more . Being near sea level or in a moist or dusty environment makes it difficult , not to mention sitting indoors watching tv or playing video games . But the green segment is merely a color shift , not a flash . Being the color of the clear sky , and hence the very happiest of colors ; in the abstract , blue is a very nice color . I'm so accustomed to hoping for green that blue at Sunrise can have a slightly surprising aspect , despite being so welcome . I've seen roughly 2 and a half green flashes . One was a green flash , one was a weaker green flash and one was a blue flash . http://www.satobs.org/seesat/Aug-1999/0099.html On a flight between Philadelphia and Washington , I once saw 8 green segments in fairly rapid succession beyond a very distant cloud . I offer no explanation about how that could happen , beyond noting that the airliner was not noticably oscillating up and down . I posted this before my experience base had expanded sufficiently to allow me to speak as specifically as I now do : Newsgroups: sci.astro Date: 1995/03/31 Subject: Re: Green Flash Revisited Anyone who has expectations of how a sunrise or sunset will appear is bound to be disappointed. The range of phenomena is simply too great. I'm currently writing an article about the green flash and looking for a publisher (hint, hint). Here is a teaser from my log, from this last Monday; note this is a SUNRISE over a LAND horizon: 1995 March 27 11 21 30, -81.86371, 41.37355, 256 m: Sky 90% overcast, but not near the orient. At 11 21 8, an orange billowing began at the orient. This roiling-cloud-like phenomenon sometimes lasts for many seconds prior to the first bright rays reaching over the horizon. It is uncommon at sunset. It expands as it continues. At 11 21 30 green twinkles began to appear. This was the moment of sunrise. At 11 21 35, a very bright, large burst of green bloomed above the green and yellow fragments. At 11 21 40 the green had been completely overwhelmed by the yellow and pain was imminent immediately thereafter, due to the high level of illumination. Sometimes there is no bloom or burst of green, but there will be a distinct green phase. Then this : Newsgroups: sci.astro Date: 1995/09/24 Subject: Green Flash! Sun rise, land horizon; Venus set; Mars set; Ganymede Sunrise on a moderately polluted planet Sunrise this morning from Berea, Ohio, USA, -81.8637 (W), N 41.3735, 256m; very low, land horizon; 7x35 binoculars, stopwatch, WWV 5 MHz. Bright green flash, preceded by tiny orange roiling cloud. (Only rarely (except when it is cloudy) is it truly difficult to discern the location of the orient merely by inspection prior to sunrise, without considering the possibility of precalculating it, altho the notice is sometimes only a few seconds). Illumination above the orient shifted markedly to the right for a couple of minutes prior to Sunrise. At 950924 111902.1, the first bit of a very small, orange, dim (i.e., not bright), roiling cloud appeared at the orient. At 111907.1, Sun rise, the first bit of green, which was bright, appeared. Within .5s it had expanded to become a nearly horizontal, somewhat interrupted bar, which rapidly became very bright, really spectacular. At 111910.4, the green flash ended as it was overwhelmed by incredibly brilliant yellow, which terminated observations. The equinoctial Sun rise the morning before had been in some ways more spectacular than this morning, but those details will have to follow later. --- Venus set last evening was spectacular. For a couple of minutes prior to Venus set, as seen thru a tripod-mounted, 81x89 monocular, the planet was separated into multiple, highly colored, vigorously vibrating disks. The separation was so spectacular that had they not been bouncing around like crazy; at times, they might have appeared to be stacked on their edges, one on top of another. These disks were red, yellow, green, and to a lesser extent orange, and even less, blue. The altitude at disappearance, 950923 232823 must have been very low because ICE computes an altitude of -29.7', with total altitude corrections of -33.6'. I'm not exactly sure how to interpret that. --- Whenever someone tells you what they saw , what they are certain they saw , no matter how bizarre , please advise them to make observations like these for themselves and to carefully compare what they appeared to see , on the one hand , with what they know to be the physical nature of the Sun and Venus , on the other hand . And then to characterize the transparency of the atmosphere , and the fidelity of images seen through it . Another thing to keep in mind is that , although they had only 1X available , our ancient ancestors could see phenomena something like these . E.g. , I'd be quite surprised if Galileo was the first human to see the satellites of Jupiter . I consider it all but certain that someone had previously taken advantage of favorable conditions and a very distant rock to see a step disappearance of Jupiter , revealing one or more of its satellites . Whether such observers made the proper interpretation is a separate matter . Then this : There are trees low on my horizon where Mars set, so I couldn't follow it for the last few minutes. But prior to that, it was very interesting because the disk was split into various colored disks, tho not as thoroughly as Venus had been. In fact, near the time I lost sight of it, about 950924 005620, it was essentially just one disk. But what a disk. It was an incredibly highly saturated, deep red; really spectacular; so incredibly red. Often people report having difficulty seeing Mars as red, characterizing it as orange instead. On this occasion there wasn't even a ghost of a doubt; in fact it was a very deep red, way over toward the infrared. [ 950924 111902.1 = 1995-09-24 11:19:02.1 UTC ] A thought toward a proposal . NSF should commission an atmospheric survey project to record these Sunrise/set phenomena every day with a view to creating a baseline , documenting the present state of the atmosphere going forward . This would be primarily meteorological in purpose , to capture detailed information over the decades about the content and nature of the atmosphere by imaging , including spectroscopically , Sunrises and Sunsets ; and Moonrise/set , Venusrise/set , Jupiterrise/set , and Marsrise/set . It would also be capable of capturing images of the green flash . We have one atmosphere . One . Other observations . http://blog.360.yahoo.com/blog-I4JaicUoeqgoFA_O4TQKZtnyA.8-?cq=1&p=323 It is like a flashbulb from a camera, green, and rare to see. There were scientists who had never seen it before. They would jump around on the deck, because they were no longer virgins. http://www.sailblogs.com/member/accatsailor/?xjMsgID=31614 The green flash occurred just as the sun dropped below the horizon. It was almost a neon green color and gave the appearance of a slow motion green flashbulb going off. It lasted for a couple of seconds and then the horizon was back to normal. We were both excited to see it! http://www.ncyc.ca/cruising/cuba/mar_04/mar_04.htm One other "first" was when Debbie was on the wheel at sunset, and witnessed the green flash. This occurs the moment the sun disappears from the horizon, and in the red and orange glow sometimes you seen a flash, similar to a green flashbulb going off. http://www.stayadventurous.com/2010/07/sunset-sunday-my-first-green-flash-laguna-beach-california/ Just like a flash bulb photo from the 1930s, a brilliant blast of light pulsated immediately after the last edge of the sun dipped below the horizon. ... The flash also seemed to travel along the horizon outwards from the center. Brilliant and beautiful. http://www.tripadvisor.com/ShowTopic-g150792-i257-k3780628-The_Green_flash_at_Sunset-Mazatlan_Pacific_Coast.html The Green flash at Sunset ... Most of the time it is the last one second before the sun disappears, but on occasion it is like a small green flash bulb. http://www.tripadvisor.com/ShowTopic-g150792-i257-k1640416-o10-The_Green_Flash-Mazatlan_Pacific_Coast.html But sometimes it is actually a flash. Like a small green flash bulb. http://www.surfingsandiego.com/forum/printer_friendly_posts.asp?TID=2425 No worries, the Green Flash occurs at a precise moment as the sunsets. There's no guarantee that it will occur, or that you will even see it, it just kind of happens. It's like a green camera flash bulb going off, everything gets a green tinge, it's almost blinding. http://www.negril.com/discus/messages/83412/151149.html I've only seen it happen one time and that was in St Kitts. It was bright like someone taking a picture with a green flash bulb. http://www.cruisersforum.com/forums/f106/the-green-flash-20359.html The Green Flash ... Saw it once really well at 13 degrees N latitude. Never thought it was anything to speak of - until I saw a really good one. Shorter than a flash bulb but just as bright and green as green can be. http://www.fodors.com/community/caribbean-islands/ok-which-folks-among-you-have-actually-seen-the-elusive-green-flash.cfm It is, as has been stated elsewhere- an actually neon green flash, like a flash bulb. ... It's really a flash! I've seen it twice- ... The "flash" that looks like a "flash bulb" happens farless often. - - - The main ideas . Model of the Standard Atmosphere for Green Flashes and Blue Flashes atmospheric refraction : bending of incoming light by the atmosphere differential atmospheric refraction : refraction increases as the density of the transmitting medium increases . chromatic differential refraction : lower frequency light is refracted more , i.e. , through a greater angle, e.g. , by a prism . atmospheric refraction : Celestial objects appear to be closer to the zenith , i.e. , at higher altitudes . Sunrises come earlier than geometry suggests ; Sunsets come later . differential atmospheric refraction : refraction increases at lower altitudes , i.e. , near the horizon , e.g. , the Sun appears highly elliptical at very low altitudes as the lower part of the image is raised more than the upper part . chromatic differential refraction : the violet sun rises earliest , followed by blue , green , yellow , orange , and finally , the red sun . At Sunset , the red sun sets earliest , followed by orange , yellow , green , blue , and the violet sun . atmospheric extinction : scattering and absorption reduce the light from an astronomical object . The light from an astronomical object is reduced by atmospheric extinction caused by scattering and absorption . Rayleigh's Law holds that higher frequency light is scattered more efficiently . Often , extinction is augmented by water in the form of haze , fog , mist , or cloud or by dust . This is so effective that violet flashes are virtually unknown and blue flashes are very rare . The Green Segment This atmospheric model explains how the first visible segment of the rising Sun can sometimes be green , or even blue , instead of yellow , and by symmetry , the last visible segment of the setting Sun . ( It also explains why the sky is blue and why the rising or setting Sun , and light near it or near the horizon , is often orange or red , instead of yellow . ) A green segment can be a quite remarkable sight , especially on initial viewing or if unexpected . I'm not a physicist , so my judgment cannot be definitive , but the documentation of the green segment by Professor Andrew Young at http://mintaka.sdsu.edu/GF/ seems excellent to me . That site uses the term green flash to describe the green segment and does not address the green flash , except in reference to historical events . Its images show the green segment . http://mintaka.sdsu.edu/GF/explain/obs_colors.html Documents the green segment very well . Reversed in time and somewhat obscured by far-away , low trees , the sequence http://mintaka.sdsu.edu/GF/pictures/Zinkova/MZ70.jpg http://mintaka.sdsu.edu/GF/pictures/Zinkova/MZ71.jpg http://mintaka.sdsu.edu/GF/pictures/Zinkova/MZ72.jpg http://mintaka.sdsu.edu/GF/pictures/Zinkova/MZ73.jpg http://mintaka.sdsu.edu/GF/pictures/Zinkova/MZ74.jpg is very familiar to me as a typical view of the vicinity of the orient on a clear morning . Excellent documentation . http://mintaka.sdsu.edu/GF/pictures/AAS/greenflash2.jpg http://mintaka.sdsu.edu/GF/pictures/Jan7cropped.jpg http://mintaka.sdsu.edu/GF/explain/simulations/inf-mir/colors/GFcolors.html Excellent documentation . Meteorological Modifications The atmosphere is rarely completely free of disturbances which distort the view of the rising or setting Sun to a lesser or greater degree . Refraction varies with temperature , humidity , and pressure . Sometimes , especially near sea level , disconnected segments or bands , i.e. , segments of two bases , of the rising or setting Sun appear , often one above the other ; sometimes , some of these are inverted , or upside-down . These can be quite remarkable sights . Sometimes , the meteorological modifications are very complicated , making adequate description nearly impossible . Sometimes , the effects of these meteorological modifications evolve very rapidly , making adequate description of a visual observation nearly impossible . Sometimes , the meteorological modifications enhance the view . This may be a brightening of a disconnected piece or pieces of the Sun . It may be a merging of such pieces . The green flash , the true and legendary green flash , is apparently the result of a specific , rare type of meteorological modification which produces a huge increase in brightness . Other than the observations themselves , I don't claim to know very much about meteorological modification , so I'm not comfortable making judgments . The Green Flash Rarely , a green flash , or very rarely , a blue flash , may occur when the brightening is so extreme as to appear to be as bright as a flashbulb . The Green Flash is not a piece of any size ; it's a "flashbulb areal multiflare" . Once the flash starts , your eyesight is instantly blasted , and you would not be watching the gleaming for a half-second or second or so . Words fail to wholly capture this electrifying experience and it has become the stuff of legends . No one has yet described or catalogued all the meteorological modifications which may occur . Landscape Modifications Obviously , the view can be obstructed by objects near and far . Between and above distant leaves , often only green specks will appear . Ocular Modifications Obviously , the view can be distorted by imperfections in the eye and in any optical system used . At Sunset , careless viewing of the yellow sun , or yellow photosphere , can result in bleaching of photosensitive pigments in the retina , specifically erythrolabe , which can result in insensitivity to red light , which can result in perception of anomalous colors , specifically , what is recorded by a camera as yellow light can appear to be green to the eye . Prologue More high-quality data is desperately needed . Walter Nissen preliminary posting : 2013-05-08 minor update : 2013-05-11