APOD: A Green Flash from the Sun (2014 Jun 04)

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APOD: A Green Flash from the Sun (2014 Jun 04)

Postby APOD Robot » Wed Jun 04, 2014 4:10 am

Image A Green Flash from the Sun

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, as well as an even more rare red flash, was caught in the above photograph recently observed during a sunset visible from the Observatorio del Roque de Los Muchachos in the Canary Islands, Spain. The Sun itself does not turn partly green or red -- the effect is caused by layers of the Earth's atmosphere acting like a prism.

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Re: APOD: A Green Flash from the Sun (2014 Jun 04)

Postby Ann » Wed Jun 04, 2014 5:13 am

This is a fine picture which demonstrates the effects of how the setting Sun has to penetrate the atmosphere "sideways", so that the accumulated layers of atmosphere become very thick, and the apparent shape of the Sun becomes distorted in the process and the colors of the Sun get separated in layers.

Of course, me being me, I find the blue flash even more fascinating. The blue flash is rarer than the green flash, but this picture shows both.

Here is a picture of an extremely rare violet flash.

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Re: APOD: A Green Flash from the Sun (2014 Jun 04)

Postby BDanielMayfield » Wed Jun 04, 2014 7:13 am

APOD Robot wrote:The effect is typically visible only from locations with a low, distant horizon, and lasts just a few seconds.

I'm encouraged (in the hopes of seeing this effect with my own eyes someday) by the fact that it can last up to "a few seconds". The word "flash" sounds instantaneous, as in if you blink during sunset you could miss it. Are there videos showing seconds of green flash duration?

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Re: APOD: A Green Flash from the Sun (2014 Jun 04)

Postby Boomer12k » Wed Jun 04, 2014 8:18 am

Which I suppose is reasonable, as Green is after Yellow in the Spectrum....

Nice Example...

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Chappuis

Postby neufer » Wed Jun 04, 2014 11:45 am

http://www.atoptics.co.uk/atoptics/gf15.htm wrote:
<<Ozone absorbs the yellow/orange (i.e., 555–630 nm) light making the contrast between the red sun & green flash even more dramatic.>>
http://oceanopticsfaq.com/apps/environm ... -twilight/ wrote:

<<It is well known that the ozone layer protects the surface of our planet from the damaging effects of ultraviolet radiation but few people appreciate that, without ozone, the color of the zenith (overhead) sky at twilight would be a pale green/straw yellow rather than the deep, steely blue that we observe. The electronic Chappuis absorption band of ozone is intrinsically weak and has little effect on the color of the daytime sky. This band, extending from 450 to 850 nm, only becomes significant when the pathlength of sunlight through the atmosphere is dramatically increased around sunrise and sunset. At these times, the Chappuis band becomes by far the strongest feature in the visible spectrum of the sky or the setting sun.>>
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Re: APOD: A Green Flash from the Sun (2014 Jun 04)

Postby jackacme@gmail.com » Wed Jun 04, 2014 1:43 pm

Eric Rohmer made a movie in the '80s called "Le Rayon Vert." It's a typical Rohmer film - i.e., heavy on explosions and car chases -- just kidding, it's about a lonely French woman searching for a human connection. At some point she comes to believe that seeing the "green flash" will herald a change in her condition and allow her to find happiness.

Hmm, Wikipedia reveals that the film is connected to the Jules Verne novel of the same name. The characters in the film talk about the Verne story which makes the whole thing very pomo and meta, as the kids say.

http://www.imdb.com/title/tt0091830/?ref_=fn_al_tt_1 <-- film info
http://en.wikipedia.org/wiki/The_Green_Ray_(film) <-- more info

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Re: APOD: A Green Flash from the Sun (2014 Jun 04)

Postby hlwelborn » Wed Jun 04, 2014 4:27 pm

Fascinating photo; the optical illusion of the sun as a portal and the viewer looking out through it is wonderful.

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Re: APOD: A Green Flash from the Sun (2014 Jun 04)

Postby ta152h0 » Wed Jun 04, 2014 4:52 pm

can tbhis be seen from the ISS ?
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Re: APOD: A Green Flash from the Sun (2014 Jun 04)

Postby Chris Peterson » Wed Jun 04, 2014 6:31 pm

ta152h0 wrote:can tbhis be seen from the ISS ?

I think the problem is that sunrises and sunsets from ISS are nominally sixteen times faster than they are as seen from Earth. That means any flash will be extremely short and hard to see. Maybe with a video, where it could be seen frame by frame.

Optically, they are looking through twice as much atmosphere, which might change the distortion somewhat. The real deal killer might be that from the ISS, the entire troposphere is slightly thinner than the width of the Sun.
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Re: APOD: A Green Flash from the Sun (2014 Jun 04)

Postby neufer » Wed Jun 04, 2014 7:22 pm

Chris Peterson wrote:
ta152h0 wrote:
can this be seen from the ISS ?

I think the problem is that sunrises and sunsets from ISS are nominally sixteen times faster than they are as seen from Earth. That means any flash will be extremely short and hard to see. Maybe with a video, where it could be seen frame by frame.

Optically, they are looking through twice as much atmosphere, which might change the distortion somewhat. The real deal killer might be that from the ISS, the entire troposphere is slightly thinner than the width of the Sun.

http://couldntkeepit.wordpress.com/2013 ... high-view/
http://couldntkeepit.files.wordpress.co ... l_full.jpg
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Re: APOD: A Green Flash from the Sun (2014 Jun 04)

Postby LocalColor » Wed Jun 04, 2014 10:36 pm

Great image of a brief yet amazing occurrence.

hypermetabolic

Re: APOD: A Green Flash from the Sun (2014 Jun 04)

Postby hypermetabolic » Wed Jun 04, 2014 11:24 pm

In Greenland north of Thule (where I spent a year) the sun would touch the northern horizon (part of the ice cap) in August for the first time in months, moving horizontally. By walking up and down a hillside I could control the colour of the flash, from yellow through the spectrum to blue-violet and back. I spent a half hour of seeing and photographing it, alas without a long lens.


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