APOD: A Milky Way Shadow at Loch Ard Gorge (2010 Aug 23)

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APOD: A Milky Way Shadow at Loch Ard Gorge (2010 Aug 23)

Postby APOD Robot » Mon Aug 23, 2010 4:03 am

Image A Milky Way Shadow at Loch Ard Gorge

Explanation: Have you ever seen the Milky Way's glow create shadows? To do so, conditions need to be just right. First and foremost, the sky must be relatively clear of clouds so that the long band of the Milky Way's central disk can be seen. The surroundings must be very near to completely dark, with no bright artificial lights visible anywhere. Next, the Moon cannot be anywhere above the horizon, or its glow will dominate the landscape. Last, the shadows can best be caught on long camera exposures. In the above image taken in Port Campbell National Park, Victoria, Australia, seven 15-second images of the ground and de-rotated sky were digitally added to bring up the needed light and detail. In the foreground lies Loch Ard Gorge, named after a ship that tragically ran aground in 1878. The two rocks pictured are the remnants of a collapsed arch and are named Tom and Eva after the only two people who survived that Loch Ard ship wreck. A close inspection of the water just before the rocks will show shadows in light thrown by our Milky Way galaxy. Low clouds are visible moving through the serene scene in this movie.

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Re: APOD: A Milky Way Shadow at Loch Ard Gorge (2010 Aug 23)

Postby mexhunter » Mon Aug 23, 2010 4:26 am

Hi to all:
Night landscape photos is a very special flavor, such as Wally Pacholka or Tamas Ladanyi, of course including that of Alex Cherney.
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Re: APOD: A Milky Way Shadow at Loch Ard Gorge (2010 Aug 23)

Postby Chris Peterson » Mon Aug 23, 2010 4:35 am

This is a very lovely image. But I don't think it is very accurate to refer to what is seen behind the rocks as shadows. The Milky Way is a very extended source; it isn't difficult to capture its shadow in a long exposure, but the shadow you get is very broad and diffuse. This image is simply showing a reflection of the Milky Way in the water, except where the rocks are blocking the view of the sky. The dark areas are the reflection of the rocks, not the shadows of the rocks cast by the Milky Way.
Chris

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Re: APOD: A Milky Way Shadow at Loch Ard Gorge (2010 Aug 23)

Postby bystander » Mon Aug 23, 2010 4:41 am

Chris Peterson wrote:This image is simply showing a reflection of the Milky Way in the water, except where the rocks are blocking the view of the sky.

Sounds a lot like a shadow to me.
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Re: APOD: A Milky Way Shadow at Loch Ard Gorge (2010 Aug 23)

Postby Chris Peterson » Mon Aug 23, 2010 4:55 am

bystander wrote:
Chris Peterson wrote:This image is simply showing a reflection of the Milky Way in the water, except where the rocks are blocking the view of the sky.

Sounds a lot like a shadow to me.

No, a shadow would be non-specular. We're seeing the specular reflection of the rocks in the water. If instead of water, the area around the rocks was a light colored surface, we might see true shadows. But they wouldn't be shaped like the rocks- they would be very distorted because the light source is a band, not a point.

The rocks are shadowing the sky, but the dark areas behind them aren't really shadows in the usual sense.
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Re: APOD: A Milky Way Shadow at Loch Ard Gorge (2010 Aug 23)

Postby Wayne Thomas » Mon Aug 23, 2010 5:06 am

I'm with Chris. We are seeing the reflection of a dark object against the reflection of a bright background.

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Re: APOD: A Milky Way Shadow at Loch Ard Gorge (2010 Aug 23)

Postby wagedeth-the-taileth » Mon Aug 23, 2010 5:52 am

Game Show Host: For $15,000, name three famous Micky's!!

Stoner Contestant: Uuuuummm, Micky Mantel....

GSH: Thaaaaat's One!

Stoner: Uuuuhhhh, Uuuummm, Micky Rooney....

GSH: That's Two! Name just one more for 15 THOUSAND dollars!!

Stoner: Uuuuuuuhhhh......Ummmmmmmmm........ MICKY WAY!!!

GSH: What?

Stoner: MICKY WAY! You know, the candybar, Micky Way....... judges won't take that?

**LOUD BUZZER NOISE OF NEGATIVE**
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Re: APOD: A Milky Way Shadow at Loch Ard Gorge (2010 Aug 23)

Postby Peter Smith » Mon Aug 23, 2010 8:13 am

bystander wrote:
Chris Peterson wrote:This image is simply showing a reflection of the Milky Way in the water, except where the rocks are blocking the view of the sky.

Sounds a lot like a shadow to me.


No. The shadow is formed by light rays from the Milky Way falling on the rocks and water. The reflection is formed by light rays from the rocks bouncing off the water to your eye. So if you move, the reflection moves with you but the shadow stays in the same place on the water.
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Re: APOD: A Milky Way Shadow at Loch Ard Gorge (2010 Aug 23)

Postby drhr » Mon Aug 23, 2010 11:32 am

I'm with the mirror school, not a shadow. Take the light out of a room and the mirror is dark. Put a little light in and you'll be able to see the dark reflections in contrast to the light.
But... it's more romantic to call it a shadow, author's privilege (however incorrect). Kinda like a politician (if they tell the truth, are they still lying?)
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Re: APOD: A Milky Way Shadow at Loch Ard Gorge (2010 Aug 23)

Postby orin stepanek » Mon Aug 23, 2010 12:06 pm

I think it's a reflection also!
Hey; did you watch the movie? :) http://vimeo.com/14054461
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Pea Soup Fowl Weather

Postby neufer » Mon Aug 23, 2010 12:08 pm




http://en.wikipedia.org/wiki/Loch_Ard_%28ship%29 wrote:
<<The Loch Ard ("high lake") was a clipper ship that wrecked at Mutton Bird Island just off the Shipwreck Coast of Victoria, Australia. The Loch Ard departed England on 2 March 1878, bound for Melbourne. On 1 June, the ship was expecting to sight land when it encountered heavy fog. The fog lifted around 4am, revealing breakers and cliff faces. Captain Gibbs quickly ordered sail to be set but they ran aground on a reef. The masts and rigging came crashing down, which preventing the lifeboats from being launched effectively. The ship sank within 10 or 15 minutes.

The only two survivors were Eva Carmichael, who clung to a spar for five hours, and Thomas Pearce, an apprentice who clung to the overturned hull of a lifeboat. They came ashore at what is now known as Loch Ard Gorge and sheltered there before seeking assistance.

The Loch Ard's cargo included a large decorative porcelain peacock intended for the Melbourne International Exhibition. Remarkably, the peacock was recovered completely intact and was eventually able to be displayed a century later for the Victoria Pavilion at the Brisbane 1988 World Exposition.>>



http://en.wikipedia.org/wiki/Peafowl wrote:
<<Many of the brilliant colours of the peacock plumage are due to an optical interference phenomenon, Bragg reflection, based on periodic nanostructures found in the barbules of the feathers. Different colours correspond to different length scales of the periodic structures. For brown feathers, a mixture of red and blue is required: one colour is created by the periodic structure, and the other is a created by a Fabry–Pérot interference peak from reflections off the outermost and innermost boundaries of the periodic structure.

Such interference-based structural colour is especially important in producing the peacock's iridescent hues (which shimmer and change with viewing angle), since interference effects depend upon the angle of light, unlike chemical pigments.>>
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Re: APOD: A Milky Way Shadow at Loch Ard Gorge (2010 Aug 23)

Postby RJN » Mon Aug 23, 2010 1:48 pm

Chris Peterson wrote:No, a shadow would be non-specular. We're seeing the specular reflection of the rocks in the water.
...
The rocks are shadowing the sky, but the dark areas behind them aren't really shadows in the usual sense.


OK, but the rock reflections in the water would not be dark if the part of the rocks facing the camera were not in the shadow of light thrown by the Milky Way. For example, if the bright Moon was behind the photographer, the rock parts facing the camera would be relatively bright, as would their reflections in the water. - RJN
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Re: APOD: A Milky Way Shadow at Loch Ard Gorge (2010 Aug 23)

Postby biddie67 » Mon Aug 23, 2010 2:10 pm

I'm always amazed and fascinated at what details in an APOD picture can generate such interesting discussions.

If I may add my 2 cents, I would guess that the darker areas behind the rocks are mostly part shadow from the brighter light of the Milky Way and some minor part reflection with enough sky light and reflected light off the water and cliffs to lighten the back side of the rocks enough to moderate the shadow effect with a miniscule amount of reflection.

But whatever the effects, it is a beautiful photograph!!!!
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Re: APOD: A Milky Way Shadow at Loch Ard Gorge (2010 Aug 23)

Postby Chris Peterson » Mon Aug 23, 2010 2:19 pm

RJN wrote:OK, but the rock reflections in the water would not be dark if the part of the rocks facing the camera were not in the shadow of light thrown by the Milky Way. For example, if the bright Moon was behind the photographer, the rock parts facing the camera would be relatively bright, as would their reflections in the water.

Sure, like I said, there is a kind of shadowing. This is true for most of the Milky Way landscapes that have appeared in APOD (except for where the foreground was deliberately lit). Usually, the Milky Way is the brightest thing in the image, so anything in the foreground is shadowed. But what we are seeing in this image is simple reflection. I like the earlier comment about how the position of the dark areas would be different if the camera were in a different location.

Here's another way to think about it. If the Moon were in the sky, you could move around near the base of those rocks and go in and out of shadow- there would be distinct boundaries of lighter and darker areas. Is that the case in the situation here? I don't think so. If you moved around the rocks, you'd only see small sections of the Milky Way blocked. And the areas that would seem brighter or dimmer wouldn't correspond at all with the light or dark areas seen on the water. For instance, it appears that from inside the "shadowed" area behind the further rock, you would actually have a direct view of the brightest part of the Milky Way. That isn't the behavior of a shadow. There are shadows in the image- the back faces of the rocks are shadowed. But not the water.

Calling the dark reflections "shadows" kind of trivializes the much rarer cases where true Milky Way shadows have been captured, or even more rarely, seen with the naked eye.
Chris

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No clear shadows

Postby geoffrey.landis » Mon Aug 23, 2010 3:04 pm

I looked at this pretty hard, but couldn't see a shadow, only the reflection of the rocks in the water.
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Re: APOD: A Milky Way Shadow at Loch Ard Gorge (2010 Aug 23)

Postby JohnD » Mon Aug 23, 2010 3:17 pm

Reflection/shadow?
Compare with this: http://photo.net/photodb/photo?photo_id=3762166 which I think has to be reflection.
That is reflection in still lake water; the APOD is a composite of 15 second exposures of sea water, so a lot less smooth, but the average surface can still provide a reflection.

Like this pic , also of a lake but a 15 MINUTE exposure. http://www.flickr.com/photos/31449088@N08/3826534999 The lake rfelcts the pattern of the sky. If there was a big rock in the middle of Coniston, that would have been reflected too.

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Re: APOD: A Milky Way Shadow at Loch Ard Gorge (2010 Aug 23)

Postby Beyond » Mon Aug 23, 2010 3:41 pm

orin stepanek wrote:I think it's a reflection also!
Hey; did you watch the movie? :) http://vimeo.com/14054461


Way to go Orin!!!! A moving Apod - YEA! The only other time I've seen a "Milky Way" move that fast was when i used to eat them :!: :D
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Re: APOD: A Milky Way Shadow at Loch Ard Gorge (2010 Aug 23)

Postby orin stepanek » Mon Aug 23, 2010 5:27 pm

beyond wrote: A moving Apod - YEA! The only other time I've seen a "Milky Way" move that fast was when i used to eat them :!: :D

I like Milky Way's also; but I like Baby Ruth's and Snickers better. :D
I looked at the picture again and I still go with reflections. It's a tough call because it is so dark.
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Re: APOD: A Milky Way Shadow at Loch Ard Gorge (2010 Aug 23)

Postby Ann » Mon Aug 23, 2010 5:42 pm

orin stepanek wrote:I think it's a reflection also!
Hey; did you watch the movie? :) http://vimeo.com/14054461


That's a beautiful movie, Orin. Now that I've watched it, I think the bright shimmering on the waves are reflections.

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Re: APOD: A Milky Way Shadow at Loch Ard Gorge (2010 Aug 23)

Postby RJN » Mon Aug 23, 2010 6:13 pm

As Asteriskiodians might know, when I change an APOD, I try to change as few characters as possible. So for this one I added two words in the text toward the end, one of which is "reflections." Thanks again, everyone. I think the text reads at least slightly more accurately now. - RJN
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Re: APOD: A Milky Way Shadow at Loch Ard Gorge (2010 Aug 23)

Postby mihondo2010 » Mon Aug 23, 2010 10:53 pm

Shadow or not shadow, this picture is stunning ...

... and it makes a great desktop wallpaper image!
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Re: APOD: A Milky Way Shadow at Loch Ard Gorge (2010 Aug 23)

Postby orin stepanek » Mon Aug 23, 2010 11:54 pm

mihondo2010 wrote:Shadow or not shadow, this picture is stunning ...

... and it makes a great desktop wallpaper image!

True; and if you go through the archives; there are many photos to wet your appetite for wallpapers.http://apod.nasa.gov/apod/archivepix.html :D
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Re: APOD: A Milky Way Shadow at Loch Ard Gorge (2010 Aug 23)

Postby Case » Tue Aug 24, 2010 12:16 am

Image

I thought it was upside down, but of course it is a view from Down Under. :)
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Re: APOD: A Milky Way Shadow at Loch Ard Gorge (2010 Aug 23)

Postby terrastro » Tue Aug 24, 2010 7:43 am

Dear Captain and fellow Crew Members,

I have learnt something new today - not everything that looks dark is a shadow.

Having read all the comments here I looked at my image again and agree that dark blobs on the water are the reflections of the shadowed sides of the rocks. Unlike politicians I can admit to have made a mistake and thank you for pointing it out, it now puts "Milky Way shadows" assignment back on my list. I guess sand fields of the Simpson Desert, dried salt lakes or snowy hills would be good targets for capturing the real shadows cast by our Galaxy.

RJN asked me to share the story behind this picture and I am glad he did - it gives me the reason to write about something else than my embarrassing mistake :)

Ever since I took my first picture of the night sky I plan what I would like to photograph almost every day and the Great Ocean Road on the southern coast of Victoria was on the list of priority targets for a long time. I went there with my family in March this year and was lucky to catch clear skies and zodiacal light around Cape Otway ( http://www.terrastro.com/galleries/cape-otway/ ) but by the time we got to the Port Campbell National Park it became cloudy. I used the opportunity to survey the lookouts and mark the exact spots for the future. The weather along the Great Ocean Road is very changing and catching a clear and moonless night there is a difficult task.

Finally in July the forecast looked half-decent and I hopped in the car and drove some 300kms only to find thick and solid cloud cover but around 1am it cleared out and I was rewarded with the beautiful views of the Milky Way away from man-made lights. There are many more nice lookouts along the Shipwreck Coast so I am keeping an eye on the weather and will be going back.

When I came back home I had to squeeze out every captured bit of light from the raw images because the only available light was from the Milky Way. This required stacking and averaging seven images together to bring out the needed detail in the foreground. I use program called Registax for that other astro-photographers use it to process the deep-sky photographs but it works on terrestrial targets too. I also stacked and de-rotated the same seven images to minimise noise in the sky, for that I used another software tool from astro-photography arsenal called DeepSkySyacker. The individual 15-second exposures were shot with Nikon D700 camera and 14-24mm lens at f/2.8 and ISO 3200 .

I feel very grateful and privileged to have my images displayed on APOD and discussed here. It is a wonderful hobby and I get a lot of enjoyment when I do it under the night skies or process the images at the computer.

Cheers,

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Re: APOD: A Milky Way Shadow at Loch Ard Gorge (2010 Aug 23)

Postby Chris Peterson » Tue Aug 24, 2010 2:43 pm

terrastro wrote:Having read all the comments here I looked at my image again and agree that dark blobs on the water are the reflections of the shadowed sides of the rocks. Unlike politicians I can admit to have made a mistake and thank you for pointing it out, it now puts "Milky Way shadows" assignment back on my list. I guess sand fields of the Simpson Desert, dried salt lakes or snowy hills would be good targets for capturing the real shadows cast by our Galaxy.

Hi Alex- I first got interested in this subject a few years ago when some people who had been in Africa, under dark skies, reported seeing shadows from the Milky Way. I was (and remain) somewhat skeptical of this claim, because the Milky Way is such a broad source, and has a similar total brightness to the rest of the sky (from skyglow). I live under extremely dark skies, and have spent a lot of time trying to see a Milky Way shadow, with no success (although I have seen shadows from both Venus and Mercury, and from the zodiacal light). But I have imaged shadows from the Milky Way, both natural and carefully constructed. The natural image was taken under trees, on snow. The different directions made by branches make it apparent that those parallel to the Milky Way cast shadows differently than those that are perpendicular to it. So it is possible to get Milky Way shadows with typical nighttime exposure conditions. My images were technical, with no attempt at an aesthetic result. Whether you could produce an otherwise interesting and attractive image that also captured Milky Way shadows... well, there's a challenge!
Chris

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