APOD: Video of a Green Flash (2021 Nov 10)

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APOD: Video of a Green Flash (2021 Nov 10)

Post by APOD Robot » Wed Nov 10, 2021 5:06 am

Image Video of a Green Flash

Explanation: Many think it is just a myth. Others think it is true but its cause isn't known. Adventurers pride themselves on having seen it. It's a green flash from the Sun. The truth is the green flash does exist and its cause is well understood. Just as the setting Sun disappears completely from view, a last glimmer appears startlingly green. The effect is typically visible only from locations with a low, distant horizon, and lasts just a few seconds. A green flash is also visible for a rising Sun, but takes better timing to spot. A dramatic green flash was caught on video last month as the Sun set beyond the Ligurian Sea from Tuscany, Italy. The second sequence in the featured video shows the green flash in real time, while the first is sped up and the last is in slow motion. The Sun itself does not turn partly green -- the effect is caused by layers of the Earth's atmosphere acting like a prism.

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alter-ego
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Re: APOD: Video of a Green Flash (2021 Nov 10)

Post by alter-ego » Wed Nov 10, 2021 5:43 am

I don't know if post-processing was done and if it affected color over a wide spectrum, but sure appears like there's some violet tints visible, and increasing, around the perimeter as the end of the green flash approaches. It's weak enough that maybe there is actually a subtle violet flash occurring?
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Re: APOD: Video of a Green Flash (2021 Nov 10)

Post by migueloz » Wed Nov 10, 2021 5:53 am

In Thule Greenland at the end of the 24 hour sunlight time of summer the sun grazes the northern horizon horizontally at midnight and rises. Then you can change the visual position and therefore the colour of the sun by walking up and down a north facing hillside. Descending, the last bit of sun changes from white to green and blue before disappearing. Walking up the hillside reverses the sequence.

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Re: APOD: Video of a Green Flash (2021 Nov 10)

Post by Ann » Wed Nov 10, 2021 7:52 am

alter-ego wrote:
Wed Nov 10, 2021 5:43 am
I don't know if post-processing was done and if it affected color over a wide spectrum, but sure appears like there's some violet tints visible, and increasing, around the perimeter as the end of the green flash approaches. It's weak enough that maybe there is actually a subtle violet flash occurring?
There was definitely some blue at the end of that green flash, and some violet, too.

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Re: APOD: Video of a Green Flash (2021 Nov 10)

Post by rj rl » Wed Nov 10, 2021 8:39 am

migueloz wrote:
Wed Nov 10, 2021 5:53 am
In Thule Greenland at the end of the 24 hour sunlight time of summer the sun grazes the northern horizon horizontally at midnight and rises. Then you can change the visual position and therefore the colour of the sun by walking up and down a north facing hillside. Descending, the last bit of sun changes from white to green and blue before disappearing. Walking up the hillside reverses the sequence.
now that's something I'd love to experience

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Re: APOD: Video of a Green Flash (2021 Nov 10)

Post by madtom1999 » Wed Nov 10, 2021 9:00 am

I wouldnt call that a "Green Flash" OK there was a green 'prominence' above the sun but a green flash lights up the sky (or somehow floods your eyeballs). When you see one you will be rocked by it. The one I saw was associated with a green 'prominence' detaching from the main solar image but the light intensity shoots up but seems to come from the sky, not the actual solar/prominence area and last milliseconds at most.

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Re: APOD: Video of a Green Flash (2021 Nov 10)

Post by orin stepanek » Wed Nov 10, 2021 1:16 pm

greenset_pivato.jpg
Neat; I never seen one except in photos! :shock:
greenflash_parviainen.jpg
Kinda looks like a green cloud! :lol2:
bff5d074d399bdfec6071e9168398406.jpg
Pretty kitty; never saw a cat hold it's ears back like that :lol2:
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Re: APOD: Video of a Green Flash (2021 Nov 10)

Post by Chris Peterson » Wed Nov 10, 2021 1:50 pm

madtom1999 wrote:
Wed Nov 10, 2021 9:00 am
I wouldnt call that a "Green Flash" OK there was a green 'prominence' above the sun but a green flash lights up the sky (or somehow floods your eyeballs). When you see one you will be rocked by it. The one I saw was associated with a green 'prominence' detaching from the main solar image but the light intensity shoots up but seems to come from the sky, not the actual solar/prominence area and last milliseconds at most.
Whatever you're describing is not what we call a "green flash". Or at least, is not typical of an ordinary green flash, which is precisely what this video shows.
Chris

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Re: APOD: Video of a Green Flash (2021 Nov 10)

Post by Sa Ji Tario » Wed Nov 10, 2021 2:40 pm

alter-ego wrote:
Wed Nov 10, 2021 5:43 am
I don't know if post-processing was done and if it affected color over a wide spectrum, but sure appears like there's some violet tints visible, and increasing, around the perimeter as the end of the green flash approaches. It's weak enough that maybe there is actually a subtle violet flash occurring?
The atmosphere is acting as a prism but it is not still, so other colors appear here and there.
In addition, the climate must be in accordance with the angle of the Sun so that only the green color is filtered

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Re: APOD: Video of a Green Flash (2021 Nov 10)

Post by Chris Peterson » Wed Nov 10, 2021 2:47 pm

Sa Ji Tario wrote:
Wed Nov 10, 2021 2:40 pm
alter-ego wrote:
Wed Nov 10, 2021 5:43 am
I don't know if post-processing was done and if it affected color over a wide spectrum, but sure appears like there's some violet tints visible, and increasing, around the perimeter as the end of the green flash approaches. It's weak enough that maybe there is actually a subtle violet flash occurring?
The atmosphere is acting as a prism but it is not still, so other colors appear here and there.
In addition, the climate must be in accordance with the angle of the Sun so that only the green color is filtered
If the green is dispersed, so are the shorter wavelengths. They usually just aren't visible because the sky background is too bright and our eyes have low sensitivity to them.
Chris

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Re: APOD: Video of a Green Flash (2021 Nov 10)

Post by neufer » Wed Nov 10, 2021 3:57 pm

Chris Peterson wrote:
Wed Nov 10, 2021 2:47 pm
Sa Ji Tario wrote:
Wed Nov 10, 2021 2:40 pm
alter-ego wrote:
Wed Nov 10, 2021 5:43 am

I don't know if post-processing was done and if it affected color over a wide spectrum, but sure appears like there's some violet tints visible, and increasing, around the perimeter as the end of the green flash approaches. It's weak enough that maybe there is actually a subtle violet flash occurring?
The atmosphere is acting as a prism but it is not still, so other colors appear here and there.
In addition, the climate must be in accordance with the angle of the Sun so that only the green color is filtered
If the green is dispersed, so are the shorter wavelengths. They usually just aren't visible because the sky background is too bright and our eyes have low sensitivity to them.
  • Blue, Indigo & Violet visible at the very end of the video are not clearly separated from Green.

    However, Yellow & Orange are blocked by stratospheric ozone absorption:
http://www.jameco.com/Jameco/workshop/puzzler/electronics-puzzler-ozone-solution.html wrote:
Click to play embedded YouTube video.


How did Ozzie Measure Ozone in the Air Outside His Office?

By Forrest M. Mims III

<<As Ozzie watched the traffic light cycle though its colors of green, yellow and red, his boss's [challenge to measure ozone in the air outside his office window] kept cycling through his mind. Suddenly he shouted, "Yes!" and immediately searched online for more information about the absorption of visible light by ozone.

Ozzie soon learned that James Chappuis had long ago discovered the ozone absorption feature named for him. The Chappuis ozone absorption band extends from the blue to the red region of the visual spectrum with twin peaks in the yellow at around 575 nm and the orange at around 603 nm, as shown in this chart:

This chart is a simplified version of measurements of the Chappuis band by many separate teams. References to all of them listed at here

Ozzie learned that the absorption by ozone in the visible spectrum is much less than in the UV, but with care, it is definitely measurable. He compared this new information with the colors emitted by the traffic light and found that the yellow light was closest to the peak absorption of the Chappuis band. Ozzie then designed a simple photometer that used a silicon solar cell as a photodiode...>>
Art Neuendorffer

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alter-ego
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Re: APOD: Video of a Green Flash (2021 Nov 10)

Post by alter-ego » Thu Nov 11, 2021 4:52 am

neufer wrote:
Wed Nov 10, 2021 3:57 pm
Chris Peterson wrote:
Wed Nov 10, 2021 2:47 pm
Sa Ji Tario wrote:
Wed Nov 10, 2021 2:40 pm


The atmosphere is acting as a prism but it is not still, so other colors appear here and there.
In addition, the climate must be in accordance with the angle of the Sun so that only the green color is filtered
If the green is dispersed, so are the shorter wavelengths. They usually just aren't visible because the sky background is too bright and our eyes have low sensitivity to them.
  • Blue, Indigo & Violet visible at the very end of the video are not clearly separated from Green.
    ...
I disagree with you on that. I agree with Chris that the violet/indigo colors are dispersed, and although weak and don't constitute a true flash visible to the eye, the shorter wavelengths separate enough and in the right direction (above the sun) twice during the video (0:17 and 0:29). I expect the clarity and degree of color separation would vary depending on the details atmosphere layering, and that sharply defined colors are less common. I think the violet seen could be primarily dispersed, but the "flash" fizzled because the conditions weren't good enough. This video suggests to me that violet flashes a indeed rare.
A pessimist is nothing more than an experienced optimist

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Re: APOD: Video of a Green Flash (2021 Nov 10)

Post by neufer » Thu Nov 11, 2021 2:47 pm

alter-ego wrote:
Thu Nov 11, 2021 4:52 am
neufer wrote:
Wed Nov 10, 2021 3:57 pm
Chris Peterson wrote:
Wed Nov 10, 2021 2:47 pm

If the green is dispersed, so are the shorter wavelengths. They usually just aren't visible because the sky background is too bright and our eyes have low sensitivity to them.
  • Blue, Indigo & Violet visible at the very end of the video are not clearly separated from Green.
    ...
I disagree with you on that. I agree with Chris that the violet/indigo colors are dispersed, and although weak and don't constitute a true flash visible to the eye, the shorter wavelengths separate enough and in the right direction (above the sun) twice during the video (0:17 and 0:29). I expect the clarity and degree of color separation would vary depending on the details atmosphere layering, and that sharply defined colors are less common. I think the violet seen could be primarily dispersed, but the "flash" fizzled because the conditions weren't good enough. This video suggests to me that violet flashes a indeed rare.
The green "flash" stands out primarily due to:
  • 1) our eyes' sensitivity to green light and
    2) stratospheric yellow/orange absorption of the Chappuis ozone absorption band.
Art Neuendorffer