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

[APOD Robot]

Mysterious Green Patches on the Sky

Explanation: What is it? Some surely natural phenomenon has appeared in a video that, so far, has defied clear identification. The above time-lapse video was made to record Perseid meteors above Hopewell Rocks in New Brunswick, Canada late this summer. The video, which ran from 9:30 pm August 11 to 3:00 am the next morning, records several meteor and satellite streaks beyond a picturesque background. Each image records a 30 second exposure. At about 25 seconds into the video, however, an unusual patchy green glow appears to cover the sky. Possible explanations include airglow, aurora, lighting from an artificial or natural source, or something completely different. 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. If you have insight into what might be causing this phenomenon, please contribute to the discussion.

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Here are some notes from the photographer copied here for convenience. Original post here.

Good evening,
I am the photographer who created this video. I'd like to thank everyone for actively helping solve this curiosity. Many questions have been asked so I will try to fill in some of the gaps.
I am a professional photographer who lives and works near The Hopewell Rocks in New Brunswick, Canada. A gentleman was in the park early this season and introduced me to the fun of night photography. I played around with the technique with pleasing results so I decided to try a time lapse video. My first attempt was done during a new moon in early July. I started rather late in the night and went through till dawn. It can be viewed here: https://www.youtube.com/watch?v=_4N5rCm5b7g
I had a small glitch in the evening resulting in me losing 7 minutes of photography. This shows in the video as a jump in the stars just as the milky way passes over Lover's Arch. Being a little on the anal side, this bothered me enough that I felt I wanted to re-do it.
On the evening of August 11th (and into the morning of the 12th) I set up my equipment again. The Hopewell Rocks is situated on the Bay of Fundy which is known for the highest tides on the planet. I set up my camera (Canon 5D mkII) on a tripod down on the shore facing approximately South East. I had the tripod at a height where the tide would rise around it but the camera would be above the high tide mark. I could have set up the tripod above the high tide mark but then I would not be pointing into the sky and still having the Rocks in the foreground. Please keep in mind I was creating this for aesthetics, not a scientific experiment. I set my ISO to 5000, the shutter speed to 30 seconds and the fstop to 4.0 (canon 17-40 mm lens at 17mm focused at infinity). I knew my first hour would be severely overexposed but as the sunset disappeared, the exposure would eventually be right for the remainder of the evening. The results were a gradual fade from white to night sky. I took my first shot at 9:19 pm and continued to take one shot every 40 seconds until 3:08 am. I had set up two small Colman battery powered LED lanterns to illuminate the rocks. They are the source of exposure on the rocks and beach.
It was a beautiful evening, quite warm and no moisture built up on the lens. I was awake and present for the entire event. The camera was being controlled by a laptop and I checked it on occasion to see that everything was working. When opening the laptop, occasionally the screen would add a bit of light to the closest rocks (explaining small fluctuations in foreground exposure). As the tide rose, I did not see the green "clouds" with the naked eye but it was extremely dark and the camera's sensitivity was allowing it to capture more than I was seeing. The tide was coming in with one to two foot waves and I realized that my camera would not survive the entire evening. I stood in water up to my waist, supporting the tripod but eventually the waves forcibly moved the camera and my shoot was over. It is worth noting that as the tide rose, it physically moved my foreground light (changing my foreground exposure as noticeable on the right hand rock surface).

When I got home and processed the photos, I did the following to all 508: Set white balance to 4350, increased the exposure by 15%, added a bit of fill light (midtones +45), and increased the saturation by 10%. When I turned them into the video, I faded to black at the very end to make it more pleasing to the viewer.

Here are links to two stills. One is prior to the arrival of the green. The other during.

Http://www.creativeimagery.ca/Persieds_367.jpg
Http://www.creativeimagery.ca/Persieds_424.jpg

[Beyond]

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

[Night eyes]

It looks like an aurora.

[Nitpicker]

Lovely APOD.

As others noted when this video was first submitted, the green patches appear to coincide with the tide rolling in. It was suggested that the green patches were from bioluminescent algae churned up by the tide, and reflected onto the clouds. This sounds most plausible.

Having said that, my own minor experience messing around with DSLRs and longish exposures of lowly lit objects, often yields unusual, and rather lovely colours. So, if algae is ruled out convincingly by others, I'd be tempted to suggest it could be an artefact of the camera sensor.

[Dave Shaffer]

nitpicker may be on to something: long exposures, especially at high ISO can do strange things. Among other things, the camera CCD sensor chip will heat up as time goes by, for long exposures, which might shift the coloration of "strange things."

Can the author fill us in on the details of his camera: brand & model, what ISO was used, any in-camera (or external) noise reduction processing, what color balance, etc.

[Rob Burridge]

This looks like some sort of reflection (maybe in the optics?) from the tide as it comes in -- notice how it starts on the left when the water is starting to come in. Also, the rock on the right seems to really get lit up for a while toward the end. Why is that? Possibly a similar light source to what's affecting the camera.

[Ricardo M Ramirez]

One thing I'll note is it seems to happen as the tide comes up almost like a reflection off the water directly in front of the camera. Could be a reflection from the light shining on the Rocks which does look greenish too!

[matthank]

I'd say that was an aurora.

I have looked at auroras literally hundreds of times in my job as a weather observer in northern Manitoba. Oftentimes you can clearly see clouds silhouetted against the green glow, and I believe that is what is happening here.

[kkeeee]

I've noticed that on really humid nights photos of the Moon turn out with a green hue. Perhaps a brief patch of humid air caused the green glow.

[Ms Emm in Oz]

Surely must be an aurora? I've looked at many videos of auroras (never having seen one), and that is what it looks like to me.

[Curly G]

I agree that there is a strong correlation with the tide, but there are also some good arguments for an artifact of the digital camera. I would think that this could be resolved with experimentation - go to the same location, with similar tidal and weather patterns, and attempt to reproduce the effects, while also diligently recording all atmospheric phenomenon (temperature, winds, humidity). Then try the experiment again at different locations.

Surely all that government funding could be put to good use!

[HellCat]

Any possibility that we're seeing noctilucent clouds reflecting the green band?

That said, my number one choice is an auroral fragment trying to break free...

[Curt]

My guess is the light source that is hidden behind the foreground rock, illuminating the other rocks with a greenish hue, is then reflecting off the incoming tide water, and illuminating the bottoms of the low clouds (fog) hovering just above the waters.

[LedZeplin]

My guess before I read the other replies was clouds or haze with the white balance on the camera causing the green tint. Some of the other ideas are fun, but I'd ask what rules out a simple camera error. Is there an eyewitness who corroborates that the camera captured accurately what was observed with a human eye?

[Aristaeus]

Anything I said would be a pie-in-the-sky guess, but I think LedZeppelin's question needs to be addressed.

[Beyond]

My guess before I read the other replies was clouds or haze with the white balance on the camera causing the green tint. Some of the other ideas are fun, but I'd ask what rules out a simple camera error. Is there an eyewitness who corroborates that the camera captured accurately what was observed with a human eye?

http://asterisk.apod.com/viewtopic.php?f=29&t=32027

[totoleg]

My guess is the light source that is hidden behind the foreground rock, illuminating the other rocks with a greenish hue, is then reflecting off the incoming tide water, and illuminating the bottoms of the low clouds (fog) hovering just above the waters.

i agree with your observation, curt. i just like to add that probably the light source hidden behind the rock was placed in order to illuminates other rocks in order to give/contribute artistic effect on the video, however, it accidentally or unintentionally light-up the incoming low clouds.

[FLPhotoCatcher]

Since it's moving steadily in one direction, it's most likely not a camera artifact.
The clouds are moving right-to-left, so it doesn't seem to be cloud related.
Bioluminescence would not be bright enough to reflect off the clouds, and also, it's more blue than that.
I would guess it's some faint aurora.

[geckzilla]

I agree that there is a strong correlation with the tide, but there are also some good arguments for an artifact of the digital camera. I would think that this could be resolved with experimentation - go to the same location, with similar tidal and weather patterns, and attempt to reproduce the effects, while also diligently recording all atmospheric phenomenon (temperature, winds, humidity). Then try the experiment again at different locations.

Surely all that government funding could be put to good use!

Hah, good luck getting funding from anyone for such a frivolous experiment. That's what we're here for. Low quality, pro bono work.

[Scootra]

I, too, think that the background lighting is responsible for the greenish effect towards the end. Notice that the distant rock is also green as soon as the sunlight fades, then a similar green develops as the tide comes in. Perhaps there may be some moisture forming on the lens surface as well near the coldest part of the morning when the humidity also seems to be increasing as indicated by the low clouds drifting by.

[somebodyshort]

I take it the camera is facing west, southwest? Aurora not likely. It looks like there is a light over the horizon, I take that' St John.

[DustofBrooklyn]

Not to be picky about the video, because it was great, but if you pause around 29 seconds as the video starts to fade you can see signs that point to editing as the cause. Not intentionally, of course. But the incoming tide with clouds would throw off the balance and cause the colors to distort. And it also seems clear that a series of adjustments being made that alter other areas. With that being said, I hope I am dead wrong and it turns out to be trailing particles of Swift-Tuttle colliding with and exciting the thermosphere or something fun like that.

[Nitpicker]

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

[Tarquin]

High up cirrus clouds?

Angry birds?

[Man in Black]

Clearly it's swamp gas reflecting the light from Venus.