APOD: Mysterious Green Patches on the Sky (2013 Sep 30)

[chris_talarski]

It's aurora undoubtably, I don't understand why this is a "mystery"

[scopemaker]

The green looks like something I've seen where auroras become "flashing". I saw this during the 1990-1991 solar max. After photographing and all night, all sky aurora (from Aurora, Illinois, by the way), the sky flashed from north to south in what visually was white patches. I ran out of film, so never tried to get the phenomenon. It lasted for about 45 minutes before going back to dazzling colors. But I'd bet that what it is.

[Nitpicker]

This APOD is an attempt not only to solve this intriguing sky riddle, but to measure how powerful the APOD readership is as a citizen-science, collective-intelligence engine.

I remain unconvinced that this intriguing sky riddle has been solved for sure. Too many possibilities if you read all the comments. Although I have learned quite a lot, I only bet on a certainty.

As to the second stated purpose of this APOD, I feel more confident in saying that the collective intelligence of the APOD readership is much, much smaller than the sum of its parts.

[Beyond]

As to the second stated purpose of this APOD, I feel more confident in saying that the collective intelligence of the APOD readership is much, much smaller than the sum of its parts.

I give that a two ROFL rating.

[GKnightCanada]

1. If you watch just before the big green splotch, there are two much smaller green splotches that appear and disappear.

2. There are dozens of observatories all over the world providing 7/24/365 coverage.

If this was something happening in the upper atmosphere, why would observatories not have ever seen anything like it?

It is either something exceedingly rare or something that doesn't occur around observatories, as opposed to something global and common.

3. It can't be something that commonly occurs in the upper atmosphere because we have so many observatories, and it would be a well known phenomenon. (Although it could be a known phenomenon that local conditions are disguising.)

Observatories tend to be built at high elevation in mountains.

So likely this is something to do with the lower atmosphere, perhaps something to do with the nearby presence of the ocean or the forest.

4. Maybe the green is much closer than we are assuming, like a few hundred feet away, and we only notice it when it is illuminated by a green light.

Maybe fog or engine exhaust illuminated by some kind of green flare.

5. If it really is happening in the upper atmosphere or beyond, it must be something very very rare to have never been seen before.

6. I've seen aurora borealis many times. On my monitor the green appears to be the same green often seen in aurora borealis. But it doesn't have the thread or curtain-like look. It is also very brief.

[GKnightCanada]

We obviously need more data.

If they experts who watch the sky for a living can't identify this it is something not happening or not visible where they are.

Has there been any further attempt to do more recordings at the same site?

Exact same site, same camera, same lights, same rising tide.

[GKnightCanada]

I think lhansen » Mon Sep 30, 2013 10:32 pm probably has it. Flood lights reflected off the surface of the rising tide reflected back to the camera from a slight mist in the atmosphere [probably less than 200 feet above the water].

That is a good hypotheses that can be tested by going back out there and repeating the shoot under similar atmospheric and tidal conditions (perhaps repeating it a few times).

Would the photographer be up for trying that? Unless we do the experiment we'll never know for sure, and I've very curious.

[JohnWindam]

Triffids!

[geckzilla]

I think lhansen » Mon Sep 30, 2013 10:32 pm probably has it. Flood lights reflected off the surface of the rising tide reflected back to the camera from a slight mist in the atmosphere [probably less than 200 feet above the water].

That is a good hypotheses that can be tested by going back out there and repeating the shoot under similar atmospheric and tidal conditions (perhaps repeating it a few times).

Would the photographer be up for trying that? Unless we do the experiment we'll never know for sure, and I've very curious.

Probably the best you are going to get is by reading the quoted post from the photographer in the very first post of this thread. And they weren't flood lights, they were small LED lights. Much dimmer than the video implies.

[matty]

Some type of rare aurora effect?

[Lame Nickname]

You could try recording the video again with a blue light, or purple light to illuminate the rocks, then see what gets recorded. If the sky still lights-up green, then it might be atmospheric Soylent Green.

[johnpombrio]

If the color was grey instead of green, the answer would be obvious, high cirrus clouds moving in. The only question after that is why are they green. With a camera's ISO cranked up to record the faint light show going on, color and saturation issues are bound to show up. It's high clouds with the camera causing the green hue.

[George Kinge]

http://asterisk.apod.com/viewtopic.php?f=29&t=32027
I agree with the back ground lighting reflecting off the tide coming in.

[Guest]

Possibly an anomaly in the image, green bleeding in to the clouds forming from the surrounding foliage framing the scene. My vote is on it being ice clouds so high they are reflecting an aurora farther north. But what do I know, I'm just a simple genius.

[Guest]

...or ice clouds reflecting/refracting a Green Flash of the rising sun?

[cathalferris]

Okay - there are some hypotheses that are way off-base. Let's think this one through, in an intelligent and logical manner..

There's unlikely to be any high-altitude cloud present - the star images do not spread or dim appreciably in the video. Neither is there any obvious dimming of the aircraft trails as they pass through that area in the FOV. If there was any water droplets or ice crystals present, then there would be a dimming and spreading-out of the star images at different points in the image, and we simply do not see that. We would expect to see some attenuation of the stars if there was enough cloud present to appreciably reflect any local light.

The output from a pair of omnidirectional camping LED lanterns just isn't enough to illuminate a cloudbank at 15-30km away, which would be the distance of the lower reaches of the green glow if it were the result of illuminated high-level cloud. Just use the high-school geometry to work out the approximate distances.

Aurora - this is certainly more possible, but working against it is the low Kp that was seen for that night, coupled with the camera being farther from the magnetic pole than e.g. Scotland. I've not seen any record of aurora past the zenith from Scotland let alone somewhere farther south geomegnetically, so we can safely discount aurora as the glow. The magnetic field wasn't disturbed enough for southerly-visible aurora at that geomagnetic latitude.

HAARP-related stuff? It's not anywhere realistic.

Algal glow? Not realistic either - if this was to be backscattered by the atmosphere (given we see no clouds present as per my first point) then that glow would have made headlines as well as being easily picked up by satellites and ISS. We just do not see algal glows as bright as city lights, and this is about the brightness needed for the effect seen.

Tidal synchronicity? Given that the green glow is above the mid-level clouds that appear near the end, suggests a minimum distance and height to the glow, and this is above that at which any tidal local weather effects are seen.

Man-made lighting? The glow, while patchy, is fairly even in it's max glow across a fairly large swathe of sky. To achieve this evenness, it's either a *lot* of light energy from one point carefully shining to give an even illumination. This is not trivial. Try to get an even glow across a wall from a flashlight or other small-sized light source. To get the evenness the edges need to get a lot more light energy than the centre, and there's not many realistic options for this. A large light source such as a large city could provide the level of evenness, but that would give a different colour. And we know that there are not any really large cities lit by mercury lights anywhere near the camera. (Eastern Europe / Japan would be the few that would have more mercury than sodium, with a size big enough to evenly illuminate this much sky.

What's left?

I'm trying to get any raw data from the Suomi NPP satellite sensor suite for the night in question, as that would certainly help to pin down any sources of the glow.

I'm saying it's airglow, given what is known about the appearance and behaviour of airglow. Occam's razor comes into play here - it's the simplest solution that fits the observation.

Can anyone give logical reasons why it isn't airglow?

[jean-daniel pauget]

my experience of shoreline and tidal timelapses tells me it's rather common to have several layers of clouds going in opposite or crossed directions, particularly at sunset and sunrise.
the green glow may look autora alike, but the shape is very cloudy to me rather than the usual veils auroras provide.
the green colour also looks like a reflection onto an additional filter in front of the lens, but I cannot clearly relate it to any element in the picture, even the tide.
Usually such reflections are easily correlated as geometric transformations of one bright part of the image.

so my best guess is : a layer of sunrise smog entering a beam from some remote public lighting ?

http://www.flickr.com/photos/yorgda/set ... 144474583/
http://disjunkt.com/jd/

[chefchris]

i think it is smog and the refracted light makes it appear green.

[cathalferris]

It's not related to sunrise - the timeframe of the video is far too long for it to be sunrise-related - especially when the photographer confirmed that the exposure time was constant. Dawn related phenomena would be viewed towards the north east at this latitude and time of year, not the southeast.

Smog doesn't refract as such. It generally absorbs shorter-wavelength colour ranges, and tends to give a muddy red colour when you push the saturation. You simply do not get a pure green from smog. Also, smog would show itself in spread-out star images from scattering of the starlight, and we don't see that to any appreciable extent.

[geckzilla]

Can anyone give logical reasons why it isn't airglow?

A valid point was made in the original thread about it not having the usual waves that airglow presents with. I countered that with the idea that we are viewing it from an unusual angle. It's true that it's an atypical airglow pattern if it's airglow, though.

The idea that lights are reflecting off some very tenuous cloud cover is still pretty solid, too. There wouldn't necessarily have to be any scattering of airplane lights or stars or the scattering could be so faint that the video size and compression kills the effect. It would be nice to have a few stills at original resolution to inspect visual anomalies without the compression interfering so badly.

[gimpyskipper]

I too live near the Bay of Fundy and I like most of the people are in awe of this seascape. At this location the maximum tide would be about 30ft. And when these huge tides come in, the cold waters (about 10c even in summer) often impacts the moist air and causes fog. In this case the fog appeared merely as wisps and are of course, quite low.

The light that the photographer causes the rocks, that are normally reddish ocher in daylight to appear greenish. This can be seen in the video.

Thus the light, reflected from the rocks, illuminated the incoming fog in greenish light

[PhysicsChris]

Could it be noctilucent clouds? The green colour being there because of the original colour cast.

[Curt]

Seems to be looking about NE (based on sky motion) from a latitude of N46. Can Aurora Borealis be observed from so far South?

Based on the topography of the location if the camera had been pointing NE much of what you would be able to see is the cliff wall. That said, the camera seems to be pointed mostly towards the south as it is looking out into the bay, possibly SW from approx location 45º49'01.66"N 64º34'29.32"W. Regarding the Aurora Borealis, yes, it can be seen this far south but only rarely, and never if you are not looking towards the north.

"When you hear hoofbeats think horses, not zebras."

[Steve Dutch]

Since we don't see any bioluminescent algae in the water, I doubt there were enough to light up the clouds, and there weren't significant clouds until the very end of the video anyway. The form isn't very typical of an aurora, but both the color and appearance are very similar to other videos of airglow.

[geckzilla]

"When you hear hoofbeats think horses, not zebras."

I'm being pedantic but zebras are horses and this statement is also biased against people who observe hoofbeats in Africa or at a zoo. Perhaps it would be more appropriate to say when you hear hoofbeats it's probably not Sleipnir.