Starship Asterisk*

http://apod.nasa.gov/apod/ap090127.html

Another great APOD from Wally Pacholka. The complete panorama available here. I assume the bright area to the right of Jupiter is our galactic center.

I think most Milky Way photos are outstanding. 8) This one goes in my wallpaper file.

Orin

bystander wrote:http://apod.nasa.gov/apod/ap090127.html

Another great APOD from Wally Pacholka. The complete panorama available here. I assume the bright area to the right of Jupiter is our galactic center.

This seems to be the least convincing of a whole series of unconvincing
professional Milky Way digital composites that have made there way to APOD.

(I wonder what they charge to put me & my family in the foreground?)

@ neufer : why the negativity ? Gorgeous picture. It's now my desktop background.

The looming mountain mass in the center background is actually Mauna Loa. You're looking south to the Big Island and Mauna Loa is the first mountain you'll see. Mauna Kea is in the center of the island and is always snow capped.

arcanne wrote:@ neufer : why the negativity ? Gorgeous picture. It's now my desktop background.

The looming mountain mass in the center background is actually Mauna Loa. You're looking south to the Big Island and Mauna Loa is the first mountain you'll see. Mauna Kea is in the center of the island and is always snow capped.

Or I don't doubt that they are real photos of real places...
but why do they have to paste on a phony backdrop
(especially one with crystal clear stars right down to the horizon)?

neufer wrote:Or I don't doubt that they are real photos of real places...
but why do they have to paste on a phony backdrop
(especially one with crystal clear stars right down to the horizon)?

Although I agree the picture is probably a composite, why do you think the backdrop is phony?

bystander wrote:

neufer wrote:Or I don't doubt that they are real photos of real places...
but why do they have to paste on a phony backdrop
(especially one with crystal clear stars right down to the horizon)?

Although I agree the picture is probably a composite, why do you think the backdrop is phony?

I think they have a nice generic Google map (or two) type picture of the Milky Way
which they photoshop as the background for a wide variety of scenic foregrounds.
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Check out the lake star reflections:

http://tinyurl.com/dythfd
http://antwrp.gsfc.nasa.gov/apod/ap080729.html
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I wanna go back to the little grass shack I left in Maunakalulakkaleeka
(or whatever the name was)
where the Humuhumunukunukuapuaa go swimming by
(beneath a starlit sky)

I might almost have been willing to agree with the Big Bang concensus for a post on the Big Island .. good thing I didn't know how beautiful Hawaii is.

neufer wrote:

bystander wrote:http://apod.nasa.gov/apod/ap090127.html

Another great APOD from Wally Pacholka. The complete panorama available here. I assume the bright area to the right of Jupiter is our galactic center.

This seems to be the least convincing of a whole series of unconvincing
professional Milky Way digital composites that have made there way to APOD.

(I wonder what they charge to put me & my family in the foreground?)

I second the motion for authenticity.

Again I find myself defending Mr. Pacholka. With 31 mentions on APOD and 59 on The World At Night (TWAN), I find it hard to believe Mr. Pacholka would need to fake anything or use phony backdrops. I refer you to Wally Pacholka's reply to False Kiva APOD 9/29 discussion and APOD: 2008 Sep 29 - A True Image from False Kiva

To a point, longer exposures and more stacked frames increase detail. Beyond that point, saturation increases and detail decreases. This composition may have gone past the optimal point for detail, but it was the artist's choice.

It seems to me that an all-night exposure or all-night set of frames would include stars that, in any particular snapshot, would be below the eastern or western horizon. So it's composer's choice how close to the horizon to show stars in the final picture, isn't it?

apodman wrote:To a point, longer exposures and more stacked frames increase detail. Beyond that point, saturation increases and detail decreases. This composition may have gone past the optimal point for detail, but it was the artist's choice.

It seems to me that an all-night exposure or all-night set of frames would include stars that, in any particular snapshot, would be below the eastern or western horizon. So it's composer's choice how close to the horizon to show stars in the final picture, isn't it?

Yes, apparently these Pacholka "photographs" are professionally stitched together stacked frames of, at least, a dozen separate Pacholka "photographs" taken at different times & exposures (; though, they were probably taken from roughly the same location & within 24 hours). This would explain the crystal clear stars near the horizon as well as the terrain blurring and other problematic features.

Wally Pacholka's reply to False Kiva APOD 9/29 discussion
http://asterisk.apod.com/vie ... 503#p97227

<<The cave is huge, so the 24 mm lens required me to take 4 separate (camera veritical) shots shooting one shot at 25 seconds and then moving the camera horizontally for the next shot and so on until I got the entire cave. Each shot was a sky/landscape shot and I had a professional lab sticth the photos together with a panoramic blending software to make it one continous horizontal shot as I am a photoshop moron.>>

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As an "actually image" they are certainly as valid as many NASA APOD "images" , e.g.:

Restored: First Image of the Earth from the Moon (APOD 2008 November 18)
http://antwrp.gsfc.nasa.gov/apod/ap081118.html

Explanation: Pictured above is the first image ever taken of the Earth from the Moon. The image was taken in 1966 by Lunar Orbiter 1 and heralded by then-journalists as the Image of the Century. Recently, modern technology has allowed the recovery of higher resolution images from old data sources such as Lunar Orbiter tapes than ever before. Specifically, recovery of the above image was initiated 20 years ago by Nancy Evans, and completed recently by Dennis Wingo and Keith Cowing who lead the Lunar Orbiter Image Recovery Project. Lunar Orbiter Image Recovery Project. Images like that above carry more than aesthetic value -- comparison to recent high definition images of the Moon enables investigations into how the Moon has been changing.

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Mars: Radar Indicates Buried Glaciers on Mars (APOD 2008 November 24)
http://antwrp.gsfc.nasa.gov/apod/ap081124.html

http://asterisk.apod.com/pos ... =9&p=99092

bystander wrote:

Dave Jerrard wrote:... If you look closely at the two crater pairs near the upper left of center of the image, you'll notice they are the same two craters - not similar, but exactly the same. Somewhere along the line, someone has modified the original image and cloned one crater pair (I suspect the craters on the right are the originals), probably to fill in some missing image data. The area behind the duplicate craters also seems to be blurred, which often occurs when cloning or retouching images. ...

I don't see any duplicate crater pairs, and the blurring appears to be blowing dust.

apodman wrote:The crater pair located above center right looks a lot like the crater pair located below center left.
Click on the image to see the full picture if the right side of the photo is chopped off.
This is cropped from the large image http://apod.nasa.gov/apod/image/0811/gl ... ro_big.jpg

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bystander wrote:Again I find myself defending Mr. Pacholka. With 31 mentions on APOD and 59 on The World At Night (TWAN), I find it hard to believe Mr. Pacholka would need to fake anything or use phony backdrops.

Indeed. Making images like this isn't all that difficult. Wally has made some artistic choices in his processing that one may like or dislike, but I'm sure he simply collected the images used for the composite at one place and over a short interval.

apodman wrote:To a point, longer exposures and more stacked frames increase detail. Beyond that point, saturation increases and detail decreases. This composition may have gone past the optimal point for detail, but it was the artist's choice.

You can stack frames forever and the detail will only increase. That operation doesn't lead to saturation. The brightest object in the frame limits the maximum exposure time of a single subexposure.

However, if something in the image is moving, that may be what limits the total exposure time- whether a single exposure or multiple subs that are stacked. In wide field sky images like this, the total exposure is limited to around a minute, depending on how large your image is and how much star streaking you will tolerate. But a minute is plenty long enough to get the Milky Way. Another trick (one I've used) is to image the sky with a longer exposure, or by aligning and stacking subs, and then combine that with an image exposed for the foreground. The "cheat" required when you do this is to mask the two exposures, so the streaked sky in the foreground shot is removed, and the blurred foreground in the sky shot is removed.

IMO there's nothing dishonest about these kinds of techniques; the final image is still an accurate representation of the scene at that time and place, adjusted to compensate for limitations of our eyes. Certainly, all deep sky astronomical images appearing on APOD share that distinction.

Chris Peterson wrote:

apodman wrote:To a point, longer exposures and more stacked frames increase detail. Beyond that point, saturation increases and detail decreases. This composition may have gone past the optimal point for detail, but it was the artist's choice.

You can stack frames forever and the detail will only increase. That operation doesn't lead to saturation. The brightest object in the frame limits the maximum exposure time of a single subexposure.

As you know, I am half a layman and half a technician on many issues, so in my efforts to be brief I can mysteriously use technical terms in a general sense and vice versa. I knew I was in trouble from the outset with "saturation" and "detail", as I am likely to be with more terms to follow, but here I go.

First, an ideal case: I take my pictures from way out in space, so there is (1) no ambient light bias and (2) no atmospheric scattering. My optics are perfect, so there is (3) no diffraction effect. My CCD is very advanced, so there is (4) no CCD bias and (5) no digital noise. My subject is (6) only distant stars that are each represented by a single pixel. My resolution (e.g., pixels per arc second) is fine enough to leave (7) more than 1 pixel of space between stars. (8) Every pixel in my field remains perfectly fixed through my time exposure, and/or I am able to align every pixel perfectly when stacking multiple frames.

In a real case, factors (1), (4), and (5) tend to limit the ability of very dim objects to be discerned. In a real case, factors (2), (3), and (8) tend to spread light over more than one pixel. In a real case, the subject may contain more than factor (6) specifies, taking factor (7) with it.

I will buy that in the ideal case saturation will never occur and detail will always increase.

But in a typical real case, for example, you can find a group of 3 or 4 stars very few pixels apart with a dimmer star in the area between them. Factor (2) randomizes the distribution of scattered light around the central pixel of each star throughout the exposure or from one frame to another. At some relative dimness of the central star, at some closeness in pixels of the stars to each other, and at some length of exposure or number of stacked frames, must not that star become indiscernible from the sum of all other effects? I imagine a person could draw some dots and use the smoothing effect in a photo editing program to demonstrate something similar.

There is also the difference between the available information detail in a digital photo and the detail my eye can see. The grouping of stars in the example will blur together visually long before they lose their identities as detectable by a data algorithm that looks for multiple maxima. A very wide range of whites and yellows on the monitor look pretty much the same. We can adjust the brightness, contrast, and gamma to help the eye see detail, but don't longer exposures and more frames tend to decrease contrast in any case? Isn't loss of contrast at a detail level irretrievable by a general contrast compensation? At some point where factors (1) through (8) collectively create a large enough effect, doesn't digital detectability suffer the same type of degradation as visual detectability?

Chris Peterson wrote:Wally has made some artistic choices in his processing that one may like or dislike, but I'm sure he simply collected the images used for the composite at one place and over a short interval.

I just wish they were clearly designated as an artistic composites.

(I defy anyone to pick out a constellation in http://apod.nasa.gov/apod/ap090127.html )

apodman wrote:First, an ideal case: I take my pictures from way out in space, so there is (1) no ambient light bias and (2) no atmospheric scattering. My optics are perfect, so there is (3) no diffraction effect. My CCD is very advanced, so there is (4) no CCD bias and (5) no digital noise. My subject is (6) only distant stars that are each represented by a single pixel. My resolution (e.g., pixels per arc second) is fine enough to leave (7) more than 1 pixel of space between stars. (8) Every pixel in my field remains perfectly fixed through my time exposure, and/or I am able to align every pixel perfectly when stacking multiple frames.

I'd get rid of (4). Any bias (e.g. dark current) can be subtracted, and any noise that the bias introduces (e.g. dark current noise) can be lumped in with (5). I'd also toss (6) as resolution doesn't matter to the argument. Above all, I'd allow the system to have some noise, and eliminate (3), as even with perfect optics you have diffraction. The other items are subject to arbitrary reduction, simply by engineering. Diffraction and noise are here to stay, and I see no point in creating an artificial world here.

If you had a perfect sensor, it would never saturate. That is, each pixel would just keep counting photons. With such a sensor, there is no maximum exposure. The longer you image, the better your S/N gets, and the better your detail gets as a result. In practice, sensors do saturate at some point, meaning there is a maximum possible exposure before you lose data. That's where stacking comes in, since stacked images can be arbitrarily deep. As a rule, with stacked images, you care about total exposure time, and again, the greater the time, the greater the information content.

The blurring effects you include: (2) atmospheric scattering and (8) tracking error, as well as atmospheric refractive effects (seeing) don't, in practice, have any impact on the above except for very short exposures. That is, for any exposure longer than a few seconds, the blurring is the same. High resolution images are possible by making many (hundreds or thousands) of very fast exposures, selecting the relatively few that beat the seeing, and then stacking enough together to get a long enough exposure time for good S/N. That is usually called lucky imaging. It is only useful for bright objects: the Sun, Moon, and planets.

But in a typical real case, for example, you can find a group of 3 or 4 stars very few pixels apart with a dimmer star in the area between them. Factor (2) randomizes the distribution of scattered light around the central pixel of each star throughout the exposure or from one frame to another. At some relative dimness of the central star, at some closeness in pixels of the stars to each other, and at some length of exposure or number of stacked frames, must not that star become indiscernible from the sum of all other effects?

No, that doesn't happen. Outside the lucky imaging example above, the longer you expose, the better the S/N. Even though the actual star images are infinitely wide, and you can expose long enough that their outer edges may be huge, and overlap each other, their peaks are still spatially separate. Pick your display settings properly, and you'll see the same distinct stars.

Chris Peterson wrote:High resolution images are possible by making many (hundreds or thousands) of very fast exposures, selecting the relatively few that beat the seeing, and then stacking enough together to get a long enough exposure time for good S/N. That is usually called lucky imaging. It is only useful for bright objects: the Sun, Moon, and planets.

Beyond the bright objects you mention, I'd have to be careful myself about the "selecting" part. Out of a myriad of choices, I might be able to find the "relatively few" that all had a similar chance artifact where I wanted to see something. They'd be denouncing my discovery of that moonlet around that dwarf planet in a minute.

apodman wrote:Beyond the bright objects you mention, I'd have to be careful myself about the "selecting" part. Out of a myriad of choices, I might be able to find the "relatively few" that all had a similar chance artifact where I wanted to see something. They'd be denouncing my discovery of that moonlet around that dwarf planet in a minute.

Yup. It used to be done manually (and often still is), but newer software is incorporating quality judging algorithms (looking at high frequency content, and other indicators) to more objectively identify the highest quality frames. Another trick is to use feature comparison to distort frames so they match others, effectively minimizing the effects of seeing. That can involve hundreds of reference points on some images- suffice to say the computational requirements are quite high (but well within what modern desktop computers are capable of). Great stuff for lunar and planetary imagers, who are now able with small telescopes and inexpensive equipment to produce shots that only space-borne telescopes could manage a few years ago.