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Are most of astr. pict. real for the naked eye?
Posted: Thu Dec 30, 2010 1:22 pm
by moontrail
Are most of astronomy pictures real?
Let's say real for the naked eye, considering the case that it could be able for the human being to come closer enough to the sidereal objects.
Disregarding indeed the false colour images, and taking into account only the light enhancement, maybe even a black shoe on earth under sunlight with enough light enhancement will result in a bright full colourful piece. Is this the "real" image of the black shoe perceived for a human being?
Maybe it is not only me interested in knowing the aspect of the universe just to the naked eye close enough to the sidereal objects.
Thank you and all the best for 2011!
Re: Are most of astr. pict. real for the naked eye?
Posted: Thu Dec 30, 2010 3:27 pm
by Chris Peterson
moontrail wrote:Are most of astronomy pictures real?
Let's say real for the naked eye, considering the case that it could be able for the human being to come closer enough to the sidereal objects.
Disregarding indeed the false colour images, and taking into account only the light enhancement, maybe even a black shoe on earth under sunlight with enough light enhancement will result in a bright full colourful piece. Is this the "real" image of the black shoe perceived for a human being?
Maybe it is not only me interested in knowing the aspect of the universe just to the naked eye close enough to the sidereal objects.
No, most astronomical images are not representative of how the eye would see the same objects. That's not to say they aren't "real", though! They are as real as what we see, just different. Would you consider bacteria under a microscope to be unreal simply because they go unseen without that tool?
While objects get brighter as you get closer, they also get bigger. The result is that their surface brightness is unchanged. No matter how close you get to something, it will never look different than it does through a telescope from Earth- and deep space objects are simply not bright enough to trigger human color vision. To our eyes, the Universe is a gray place, peppered with weakly colored stars.
Re: Are most of astr. pict. real for the naked eye?
Posted: Sun Jan 02, 2011 7:14 pm
by Evan
What Chris describes is true for what are called "extended objects" such as entire galaxies, globular clusters, nebula and any deep sky phenomena that is spread over a large volume of space. However, for compact objects such as individual stars, planets and their moons, asteroids and perhaps accretion disks of black holes the story is different.
For such objects the closer you are the brighter the object will appear. What looks to us here to be a point source of light will resolve to a clearly visible object when viewed from a sufficiently close distance. This is very clear when observing planets that appear starlike to the unaided eye. Add some magnification and light collecting ability and the colours and details become visible. That can be directly translated to a particular viewing distance from the object that would produce a very similar visual result to the human eye.
Re: Are most of astr. pict. real for the naked eye?
Posted: Sun Jan 02, 2011 7:23 pm
by Evan
Sorry about posting the above as a guest. I didn't realize that I wasn't logged in or that this forum allows guests to post.
Re: Are most of astr. pict. real for the naked eye?
Posted: Sun Jan 02, 2011 8:31 pm
by Chris Peterson
Evan wrote:What Chris describes is true for what are called "extended objects" such as entire galaxies, globular clusters, nebula and any deep sky phenomena that is spread over a large volume of space. However, for compact objects such as individual stars, planets and their moons, asteroids and perhaps accretion disks of black holes the story is different.
For such objects the closer you are the brighter the object will appear. What looks to us here to be a point source of light will resolve to a clearly visible object when viewed from a sufficiently close distance. This is very clear when observing planets that appear starlike to the unaided eye. Add some magnification and light collecting ability and the colours and details become visible. That can be directly translated to a particular viewing distance from the object that would produce a very similar visual result to the human eye.
I'd agree for stars, but not necessarily for planets (at least, not within our own system). All the planets from Venus to Saturn are large enough that they are extended objects to our naked eye (even though they seem nearly star-like). These objects don't get any brighter as we magnify them. They get bigger, which is why we see detail, and because they are bigger we also see structure in their color, instead of simply seeing an "average" color with the naked eye.
The situation with stars is actually a bit complex, because the laws of optics mean they aren't point sources, but are actually extended. But their extent is determined by the optics, not by distance. For stars, a telescope doesn't model getting closer (as it does with extended objects). With the naked eye, you'd see a star get brighter according to the inverse square law, until you are close enough that it becomes an extended object, and then there will be no further increase in brightness with distance. With a telescope, however, the brightness is determined mainly by aperture. The bigger the scope, the brighter stars appear- quite different from extended objects, which don't get brighter with increased aperture.
Re: Are most of astr. pict. real for the naked eye?
Posted: Mon Jan 03, 2011 2:47 am
by Evan
Chris wrote:All the planets from Venus to Saturn are large enough that they are extended objects to our naked eye (even though they seem nearly star-like). These objects don't get any brighter as we magnify them. They get bigger, which is why we see detail, and because they are bigger we also see structure in their color, instead of simply seeing an "average" color with the naked eye.
The commonly accepted resolving power of the human eye is about 1 arc minute. Of the solar system planets only Venus approaches that apparent size at closest approach and then it is nearly invisible. None of the other planets have a large enough apparent size to be resolved as a disk at closest approach, let alone an extended object. Under more common conditions the planets are well below the resolving power of the eye. This means that the apparent brightness will be increased with increased aperture and magnification just as it is with stars.
Brightness is perceived in the eye by the fovea alone. As long as the image size doesn't exceed the area of the fovea then an increase in size will translate to an increase in perceived brightness (see next). The field of view of the fovea is about 1 degree. When a subject image on the fovea exceeds ~1.5 degrees any further increase in extent is not seen as being brighter. That means that for a range from 1 arc minute to about 1.5 degrees any increase in size of the image on the fovea
given constant intensity per unit area (greater aperture and magnification, as I stated) will be perceived as a brighter image.
Re: Are most of astr. pict. real for the naked eye?
Posted: Tue Jan 04, 2011 11:54 am
by moontrail
Thanks Chris and Evan for your replies,
It seems that the term “real” even “real for the naked eye” was not the most appropriated; maybe “in tune with naked eye perception” could have been a better option.
From your replies, the images of the Universe obtained through a telescope that resulted “similar” to the ones perceived for the naked eye through the same telescope, would be more “representative” of how the human eye would see the same objects if we were able physically to approach them enough.
In my opinion more emphasis should be put in these images in tune with naked eye perception, and also maybe APOD organization could consider some kind of general disclaimer indicating, if it is the case, that the brightness and colour of the “extended objects" showed are not supposed to be in tune with naked eye perception.
Otherways in my opinion, as most viewers (and I would even say most of the astronomy interested ones) don’t realize this lack of accuracy for the aspect of "extended objects", they result “deceived”, just through the omission of this information, and consider the images are representative of how they would see the same objects if they were able physically to approach them enough.
The Universe is fascinating enough to try to avoid this general misperception about it to the no expert viewers.
Ignacio
Re: Are most of astr. pict. real for the naked eye?
Posted: Tue Jan 04, 2011 3:27 pm
by Chris Peterson
moontrail wrote:In my opinion more emphasis should be put in these images in tune with naked eye perception, and also maybe APOD organization could consider some kind of general disclaimer indicating, if it is the case, that the brightness and colour of the “extended objects" showed are not supposed to be in tune with naked eye perception.
This view is occasionally presented here, and I confess I do not understand it. Surely, we build instruments like telescopes and cameras to extend our senses? What would be the point in limiting the images to visual equivalence? Should we blur electron microscope imagery because our eyes could never see the same thing, no matter how close or small we could get? And what about the increasing number of astronomical images made in IR, UV, or radio waves that we couldn't see at all?
IMO, the purpose of most of these images isn't to show us what an object might look like to the eye, but to teach us something about the physical nature of that object. If the image is aesthetic at the same time, that's a bonus- but just a bonus, not the main point.
Re: Are most of astr. pict. real for the naked eye?
Posted: Tue Jan 04, 2011 4:29 pm
by owlice
moontrail wrote:In my opinion more emphasis should be put in these images in tune with naked eye perception
Why?
Re: Are most of astr. pict. real for the naked eye?
Posted: Tue Jan 04, 2011 10:29 pm
by Orca
It seems to be a common view for many that reality is somehow limited to the way we perceive it with our own senses. It's an interesting human response, somewhat anthropomorphic I think. "Seeing is believing," they say. Even if one knows that ultraviolet and radio waves exist, images in those parts of the spectrum are thought of as "fake" while images in the visual part of the spectrum are considered "real."
The trouble is that we'd loose the lion's share of "reality" if we only tried to view the universe using the senses we were born with. As Chris pointed out, our instruments extend our perception of the universe.
Re: Are most of astr. pict. real for the naked eye?
Posted: Wed Jan 05, 2011 5:58 am
by Evan
I think I have a pretty good idea what Moontrail is getting at. I like to take astrophotos that represent what one could see if only our vision were more sensitive. Say, for instance, as I often explain to people, if we had "Owl eyes". Yes, that is the term I have been using for many years and not a reference to other persons, living or dead.
Below is the sort of image I mean. It was taken with a DSLR on an equatorial mount with a wide angle lens that approximates the field of vision of the human eye. While the eye can discern perhaps 2000 to 3000 stars in very good conditions the camera (and some living creatures) can see far more. The camera integrates the light that arrives, owls simply have far more rods in the retina to capture more photons.
The image has been processed to improve contrast and saturation. It was taken with my 300D which is not very good at colours.
Larger image
here.
Re: Are most of astr. pict. real for the naked eye?
Posted: Wed Jan 05, 2011 7:09 am
by owlice
My question is why is moontrail's opinion "more emphasis should be put in these images in tune with naked eye perception"? I'm assuming something informs moontrail's opinion and that there are reasons moontrail holds this opinion; I'd like to know what those might be.
For something which emits in the ultraviolet range, for example, what does "in tune with naked eye perception" even mean? Ignore the ultraviolet completely, because that is "in tune with naked eye perception"? I'm truly curious about this stance.
Re: Are most of astr. pict. real for the naked eye?
Posted: Wed Jan 05, 2011 9:00 am
by Evan
I understand your point and in truth if the criteria for astrophotos were to present an accurate naked eye view astrophotography as art would be very boring. I say art since that is a major part of astrophotography at the amateur level. This is clear from the beautiful photos posted in the most recent New Submissions thread. The object of those photos, for the most part, isn't just to inform us but to impress us. It brings to light what we cannot know without the use of tools. However, unlike measurements with callipers, the views of the universe have an intrinsic aesthetic value that is frequently emphasized even at the expense of scientific value.
That is in no way a criticism by me but it is difficult to explain the necessity to present image content in a way that most people cannot reconcile with their own ability to see. It is very much like trying to explain to someone what the images of silicon atoms in a row really represent when imaged with an atomic force microscope.
Re: Are most of astr. pict. real for the naked eye?
Posted: Wed Jan 05, 2011 11:51 am
by moontrail
For sure! No doubt about the high aesthetic value and highly valuable scientific knowledge showed in all the images, and all this information let us know more about the fascinating real Universe!
Maybe I’m wrong, but don’t you think that most people consider e.g. the marvellous colourful Hubble telescope images (dust pillars…) representative of the visual aspect of the showed objects?
Shouldn’t be this false idea set right?
Wouldn’t be they a bit disappointed and consider themselves deceived by information omission, realizing that these real formations aren’t visually there?
The mistake must be in the general assumption that images obtained through optic telescopes just approach far objects to our eyes and then approaching physically to them would had the same effect.
Ignacio
Re: Are most of astr. pict. real for the naked eye?
Posted: Wed Jan 05, 2011 3:52 pm
by Chris Peterson
moontrail wrote:Maybe I’m wrong, but don’t you think that most people consider e.g. the marvellous colourful Hubble telescope images (dust pillars…) representative of the visual aspect of the showed objects?
Many do, but I don't know if that really matters much. It is very common with these images for there to be additional details provided- the filters, the false color system, comments along the lines that the images don't appear as our eyes would see them. But some people never really get that. And I don't think it is the job of the person presenting the image to repeatedly say that.
In the end, what is important is that the images represent the structure and nature of the object. If some people think they would really look like that, let them. It doesn't really hurt anything, or alter their understanding of nature all that much.
Re: Are most of astr. pict. real for the naked eye?
Posted: Tue Jan 11, 2011 12:04 pm
by Guest
Chris Peterson wrote:moontrail wrote:Maybe I’m wrong, but don’t you think that most people consider e.g. the marvellous colourful Hubble telescope images (dust pillars…) representative of the visual aspect of the showed objects?
Many do, but I don't know if that really matters much. It is very common with these images for there to be additional details provided- the filters, the false color system, comments along the lines that the images don't appear as our eyes would see them. But some people never really get that. And I don't think it is the job of the person presenting the image to repeatedly say that.
In the end, what is important is that the images represent the structure and nature of the object. If some people think they would really look like that, let them. It doesn't really hurt anything, or alter their understanding of nature all that much.
Re: Are most of astr. pict. real for the naked eye?
Posted: Tue Jan 11, 2011 12:20 pm
by moontrail
Chris Peterson wrote: If some people think they would really look like that, let them. It doesn't really hurt anything, or alter their understanding of nature all that much.
(Excuses for the previous not intended post as a guest, perhaps I was logged for too long)
Maybe I'm wrong, but in my opinion these "some people" represent about 99.9% of the general population, and maybe 99% of APOD regular visitors, people with scientific degrees included, except professional Astronomers.
Though being wrong about most of deep space Astronomy issues doesn't really hurt anything or alter understanding of nature very much for general people, I think it would be fair to make a bigger effort regarding this so general misjudgement about the far away Universe appearance to the human eye, avoiding in some way to collaborate passively on its dissemination.
Maybe it wouldn't be so difficult to have an impact on it concerning regular APOD visitors; Just adding to some of these emblematic images (dust pillars, galaxies, supernova remnants...) something like: clicking on the image you will get an approximated image of how this image would appear to a direct observer.
In my opinion this would only enhance the Astronomy science on the public opinion. Emphasizing in this case how besides approaching us far away universe objects it enhances our sightseeing sense to perceive these fascinating and other ways hidden structures to our sensitivity limited senses.
Re: Are most of astr. pict. real for the naked eye?
Posted: Tue Jan 11, 2011 3:34 pm
by Chris Peterson
moontrail wrote:Maybe I'm wrong, but in my opinion these "some people" represent about 99.9% of the general population, and maybe 99% of APOD regular visitors, people with scientific degrees included, except professional Astronomers.
I don't agree. Most of the regular visitors to APOD will have seen references and links to narrowband filters and false color palettes dozens of times.
Though being wrong about most of deep space Astronomy issues doesn't really hurt anything or alter understanding of nature very much for general people, I think it would be fair to make a bigger effort regarding this so general misjudgement about the far away Universe appearance to the human eye, avoiding in some way to collaborate passively on its dissemination.
There are so many misunderstandings that people have which are more serious- misunderstandings that genuinely reflect a poor understanding of reality. The fact that not a single deep space image remotely resembles how it would appear to the eye, however, isn't one of them. APODs are designed to tease people into an interest for astronomy. That's really all you can do with an image and a couple of sentences.
Maybe it wouldn't be so difficult to have an impact on it concerning regular APOD visitors; Just adding to some of these emblematic images (dust pillars, galaxies, supernova remnants...) something like: clicking on the image you will get an approximated image of how this image would appear to a direct observer.
Are you volunteering? Remember that the images come from many sources- none from the site editors. Occasionally, image authors do provide alternate views of some sort, but most do not.
Re: Are most of astr. pict. real for the naked eye?
Posted: Wed Jan 12, 2011 12:17 pm
by moontrail
Chris Peterson wrote: not a single deep space image remotely resembles how it would appear to the eye
Thank you Chris for your comments.
I fully agree with all of them, except maybe about how much spread could it be, even among APOD regular visitors, the misunderstanding perfectly explained in your above quoted sentence.
Thank you for your invitation to volunteer. Even unfortunately I don’t foresee any acceptable results, I'll try with very basic image editor programs on a few deep space APOD pictures. But for sure, some APOD friends could offer, if it is the case, edited images suitable to the APOD quality standards.
Ignacio
