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Thread: The way we perceive space; the difference between telescope

  1. #31
    Wow, thanks for all the replies. There's certainly a lot to read here, but it was worth it. I guess there's little left for me to add, since I see all my questions have been answered, except perhaps to say that this thread has been most enlightening [img]/phpBB/images/smiles/icon_smile.gif[/img]

  2. #32
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    Hi Song of Distant Earth,

    As a follow-up to what I wrote earlier in answer to your question concerning how various nebula would actually look to human eyes. I did a bit more research, and my original "yes & no" answer seems to be correct. Yes, with regard to those nebula that would look to human eyes as they do in the coffee table books, technicians and scientists at the "Space Telescope Science Institute News Office" do indeed create some photos that try to approximate what the human eye would see if closer. They are referred to as pictures presenting the object's "true astronomical color." All Hubble pictures are in fact black & white. Color is added to the monochrome images via color filters. The choice of filters (for "true astronomical color pictures" and other types of color images) depends on how the particular object emits and/or reflects light. The emission of light from nebulae is at specific wavelengths, and will produce specific colors in the human eye. Hydrogen, oxygen, and nitrogen can become highly fluorescent. These gasses glow at very exact wavelengths, so the colors (to the human eye) are distinct, pure, saturated, and (if we were closer) clearly seen. This has little to do with how inherently bright the nebula is, as many emission nebulae have stars within them that would increase in perceived brightness if we were located a lot closer. Even though nebulae, and galaxies with beautiful nebulae within them are very far away and dim in telescopes, if seen at much less a distance (i.e. filling the sky,) they would be perceived very much the same as the Hubble pictures created to closely approximate "true astronomical color."

    Chip

  3. #33
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    I think when we have the technology and desire for interstellar travel, we'll also have the biological advances that allow us to interface devices directly to the brain. Imagine seeing the stars with eyes as big as the HST. Imagine growing the optical area of the brain to accept a wider spectrum so you can see the infra and ultra parts of the spectrum.

  4. #34
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    Just the other night watching the Perseids, I was struck by the sparseness of the Milky Way's center. I know there is a large amount of dust that blocks some of the light but it still seemed to lack the density that one imagines should be there. When you look at a galaxy farther away it certainly looks like it should have a more solid appearance when looking from the edge across the middle. But it appears very sparse across the center of our galaxy. I hadn't really thought about it before.

  5. #35
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    Beskeptigal,
    That "some dust" you mentioned results in 26 magnitudes of attenuation! To put that in perspective, if the Moon was attenuated by 26 mag., it would take an 8 inch telescope to see it. If the Sun was attenuated that much, it would be the same brightness as Vega.

  6. #36
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    On 2002-08-16 13:20, Chip wrote:
    Yes, with regard to those nebula that would look to human eyes as they do in the coffee table books, technicians and scientists at the "Space Telescope Science Institute News Office" do indeed create some photos that try to approximate what the human eye would see if closer. They are referred to as pictures presenting the object's "true astronomical color."
    I think you are wrong about that, but I would like to know more. Do you have some references handy?

    I would think those comments refer to the colors, not the brightness.

  7. #37
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    On 2002-08-18 14:29, GrapesOfWrath wrote:
    I think you are wrong about that, but I would like to know more. Do you have some references handy?
    Try here, from my friend Zolt LeVay at STScI


    <font size=-1>[ This Message was edited by: The Bad Astronomer on 2002-08-18 15:43 ]</font>

  8. #38
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    On 2002-08-18 14:40, The Bad Astronomer wrote:
    Try here, from my friend Zolt LeVay at STScI
    I think you used the quotes around the url, so I fixed it in my quote. I looked at his webpages, and it seems it is primarily concerned with color. Did I miss a part of it?

    If you look up at the sky, the Milky Way is visible, but it doesn't look anything like the vivid pictures that are produced from timed photographs. According to Jay Ryan's column, and others, the pictures that we are used to would correspond to those timed photos, but not to our naked eye observations which would be considerably dimmer and less impressive.


  9. #39
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    On 2002-08-18 15:06, GrapesOfWrath wrote:
    "...According to Jay Ryan's column, and others, the pictures that we are used to would correspond to those timed photos, but not to our naked eye observations which would be considerably dimmer and less impressive."
    Hi there,
    Again, you're disagreeing with a "yes & no" answer (which could also be thought of as a "no, but with exceptions" answer, and I outlined the exceptions.)

    I'm familiar with the well drawn points in Jay Ryan's cartoon, and also about long exposures bringing out more details as more photons accumulate, which the human eye doesn't do. We're actually not in disagreement. We're talking apples and oranges. You're talking just "brightness," and I'm talking about "seeing colors, and details" as the human eye can see them in distant nebula, if we were closer.

    S.O.D.E. basically asked if objects in deep space really look that way, and the answer remains yes & no depending on what you're looking for.

    There is also an article covering the topic of color in Hubble images in the current (September) issue of Sky & Telescope. See page 30 for more about "true" (to the human eye) images.

  10. #40
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    On 2002-08-18 16:54, Chip wrote:
    you're disagreeing with a "yes & no" answer (which could also be thought of as a "no, but with exceptions" answer, and I outlined the exceptions.)
    The last time I disagreed, I think it was with a "yes" answer. [img]/phpBB/images/smiles/icon_smile.gif[/img]

    I'm familiar with the well drawn points in Jay Ryan's cartoon, and also about long exposures bringing out more details as more photons accumulate, which the human eye doesn't do. We're actually not in disagreement. We're talking apples and oranges. You're talking just "brightness," and I'm talking about "seeing colors, and details" as the human eye can see them in distant nebula, if we were closer.
    We agree that "our naked eye observations ... would be considerably dimmer and less impressive"?

    S.O.D.E. basically asked if objects in deep space really look that way, and the answer remains yes & no depending on what you're looking for.
    A.S.O.D.E. gave three examples, a jpg of Antares, a scene from The Empire Strikes Back, the movie Contact, and the PC game FreesSpace II. I think the answer is that the pictures are not realistic--in that they would be considerably dimmer and less impressive--in the first three cases, but I'm not familiar with the game.

    There is also an article covering the topic of color in Hubble images in the current (September) issue of Sky & Telescope. See page 30 for more about "true" (to the human eye) images.
    I did read that article last week.

  11. #41
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    On 2002-08-18 08:04, Kaptain K wrote:
    Beskeptigal,
    That "some dust" you mentioned results in 26 magnitudes of attenuation! To put that in perspective, if the Moon was attenuated by 26 mag., it would take an 8 inch telescope to see it. If the Sun was attenuated that much, it would be the same brightness as Vega.
    I am aware the dust accounts for the absence of light in the center of the Milky Way sky stripe, but galaxies farther out look like bright spirals and such. It just struck me as being sparse, like along the same line that two galaxies can collide and while their gravity fields will distort eachother considerably there won't be billions of collisions since the stars in each are relatively sparse.

  12. #42
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    On 2002-08-18 20:36, GrapesOfWrath wrote:
    We agree that "our naked eye observations ... would be considerably dimmer and less impressive"?
    [img]/phpBB/images/smiles/icon_wink.gif[/img] Nope. At least not across every category of nebulae, but that's OK, you win. I think A.S.O.D.E. got lots of good information. I'll continue to live in the colorful universe, (some of which I've seen through my scope,) and at the same time I would never wish the "dimmer and less impressive one" on you or anyone else. Hope you get to see the actual Orion nebula on a very dark night. Have a nice day.

  13. #43
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    [quote]
    On 2002-08-19 00:28, Chip wrote:
    On 2002-08-18 20:36, GrapesOfWrath wrote:
    Nope. At least not across every category of nebulae
    I'd be interested in some examples.

    , but that's OK, you win.
    Not a contest.

  14. #44
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    Timothy Ferris described an opportunity he had to view the Tarantula nebula with the 2.5 meter Du Pont telescope at the Las Campanas Observatory in Chile. His description gives an idea of how intrinsically bright some nebulas are to the naked eye, and how much more detailed they would be if viewed closer, but still from a viewpoint outside the nebula. He writes:*

    "I gasped at the sight. Reefs of brick-red and pearl-gray gas clouds were parading by like drapery in a palace of dreams. The nebulosity became ever brighter until I arrived at the core, where sheets of gas entangled the stars of the cluster 30 Doradus. Their light had been traveling through intergalactic space for 180,000 years, dissipating all the while as it spread out, but it was still bright enough to make me squint."
    =====
    Its moments like this that make astronomy so incredible.

    * Quoted from Seeing in the Dark by Timothy Ferris. Simon & Schuster.

  15. #45
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    On 2002-09-24 04:34, Chip wrote:
    Timothy Ferris described an opportunity he had to view the Tarantula nebula with the 2.5 meter Du Pont telescope at the Las Campanas Observatory in Chile. His description gives an idea of how intrinsically bright some nebulas are to the naked eye, and how much more detailed they would be if viewed closer, but still from a viewpoint outside the nebula.
    I disagree.

    I can get the same magnification as that Las Campanas scope from my backyard telescope (OK, front yard), but the nebula don't look near as bright nor beautiful.

    The reason is the size of the scope. A 2.5 meter scope has 800 times the light gathering capability of my small 3 1/2 inch telescope--that makes the image 800 times as bright irrespective of the clear Chilean skies or quality of their optics or the magnification. That view cannot necessarily be equated with a naked eye view from closer up.

    But, still, I am sometimes overwhelmed with the views through my own scope--it has 300 times the light gathering capability of my eye.

  16. #46
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    On 2002-09-24 10:21, GrapesOfWrath wrote:
    "I can get the same magnification as that Las Campanas scope from my backyard telescope..."
    I really like Ferris' writing. I spent some time with the Orion Nebula last winter. Could detect faint whiffs of blue/gray color. Saw more detail with my naked eye through the eyepiece (without CCD.) Subjectively speaking, it was bright! Surely saw more detail than with a lower power scope. I'm sure that if we were less than a parsec from it, it would fill the sky at the same brightness, and we would see more details. Still don't understand your disagreement, but that's OK. We're all here for the fun of it as Russ says.

    <font size=-1>[ This Message was edited by: Chip on 2002-09-24 21:17 ]</font>

  17. #47
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    On 2002-09-24 12:43, Chip wrote:
    I'm sure that if we were less than a parsec from it, it would fill the sky at the same brightness, and we would see more details. Still don't understand your disagreement, but that's OK.
    Surely, being closer, the whole object would be many many times brighter? Or do you mean, through a telescope when you are one parsec away?

    Our disagreement is not unresolvable. I believe at its core it's just mathematics.


  18. #48
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    On 2002-08-11 04:58, GrapesOfWrath wrote:
    "Basically, he points out that spectacular closer-up views of galaxies are a result of artistic license only. Imagine looking at the Milky Way from just outside it. We'd be farther away from it than we are now, right? In certain directions, we can look towards the core, pretty much edge-on, but we don't see the spectacular view of the artist. Sure, I consider the Milky Way to be a spectacular view--but it's nothing like depicted in the illustrations described in the OP."
    Hi Grapes. I read through this thread recently and it appears we're at opposite ends yet ironically saying similar things, except I'm saying there are exceptions wherein actual "spectacular" objects rather than oil paintings of them, really are spectacular if we were closer to them.

    I'm not disputing the Sky & Telescope cartoon by Jay Ryan, but this question is subjective and more complicated than the cartoon. (Its a very clever and informative series by the way.) You stated: "Spectacular closer-up views of galaxies are a result of artistic license only." Sure, this is true when talking about artwork, as well as many examples of long exposures of dim objects. I'm saying many specific dim objects (like stellar nebulae) get brighter if we get a lot closer or change positions, and more details would tend to be seen. [img]/phpBB/images/smiles/icon_wink.gif[/img]

    Actually, we don't see the core of the Milky Way from here, but if we were outside or above the plane of the galaxy, and thus further away, we'd be able to make out its spiral shape, and it would appear perhaps somewhat like the Andromeda galaxy, complete with core and arms. Presuming from the observation lounge of our starship with the lights off, or from an earthlike planet with good seeing. (I don't know what "OP" stands for.)

    If A Song of Distant Earth is lurking about, I'd like to recommend two things. The BA has an article in a recent issue of Astronomy Magazine covering views of celestial objects from different hypothetical earthlike planets near or within them. Its really fun reading. And Timothy Ferris has a new book, Seeing in the Dark, which is excellent and enjoyable too. Both authors touch here and there on this topic, and I still go along with what both say based on my experience through the eyepiece.

    Happy Holidays Everyone.

  19. #49
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    The galaxy pictures shown have had the zodiacal light removed, so it isn't exactly as seen by the human eye.. There's a web book on the human eye for those interested in how we see to compare with telescopic vision. If stars flicker at the critical frequency there are psychophysics effects. (I think it only affects big bang believers, though.)

    http://www.webvision.med.utah.edu/

  20. #50
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    On 2002-12-23 00:55, Chip wrote:
    I'm saying there are exceptions wherein actual "spectacular" objects rather than oil paintings of them, really are spectacular if we were closer to them.
    OK, actual spectacular objects are spectacular. No argument there. [img]/phpBB/images/smiles/icon_smile.gif[/img]
    I'm not disputing the Sky & Telescope cartoon by Jay Ryan, but this question is subjective and more complicated than the cartoon.
    Yes and no. I think it can actually be resolved by simple mathematics, as Ryan attempts to do.
    I'm saying many specific dim objects (like stellar nebulae) get brighter if we get a lot closer
    No dispute there. Objects get brighter the closer you get.
    I don't know what "OP" stands for.
    Original Post, or, in context sometimes, Original Poster.
    And Timothy Ferris has a new book, Seeing in the Dark, which is excellent and enjoyable too.
    I actually bought that Ferris book, but donated it to the school library. Haven't been able to get it off the shelves, yet.
    Both authors touch here and there on this topic, and I still go along with what both say based on my experience through the eyepiece.
    Are you saying that they disagree with Ryan?

  21. #51
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    On 2002-12-23 09:47, GrapesOfWrath wrote:
    "...Are you saying that they disagree with Ryan?"
    If we're under the impression that the all dim "faint fuzzies" seen in telescopes on earth would always look like larger dim faint fuzzies up close, this impression is contradicted by the authors. It depends on what the "fuzzies" actually are. Some nebulae are quite bright, and if seen from a different position, would reveal more stars and details, and even some colors which the eye can see. Many galaxies have bright cores. The intrinsic luminosity might remain the same, but the amount of detail and with it, prominence of globular clusters and individual bright stars would increase. On the other side of the coin (or galaxy actually) there are for example, prominent features of the Milky Way Galaxy that are all but invisible to earthly star gazers, but would be very prominent features indeed to alien astronomers viewing our galaxy from positions in the Andromeda Galaxy. (Positions where they had a clear view of us.) They too have obscuring dust and matter to see through. Not entirely disagreeing with Ryan's main points, just enhancing the details. [img]/phpBB/images/smiles/icon_wink.gif[/img]

  22. #52
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    On 2002-12-23 17:23, Chip wrote:
    If we're under the impression that the all dim "faint fuzzies" seen in telescopes on earth would always look like larger dim faint fuzzies up close, this impression is contradicted by the authors. It depends on what the "fuzzies" actually are.
    Well the OP gave a couple examples, and I think that the answer, for those examples, should be no, they wouldn't be as impressive as depicted. Or do you disagree? With both, or one of them?
    On the other side of the coin (or galaxy actually) there are for example, prominent features of the Milky Way Galaxy that are all but invisible to earthly star gazers, but would be very prominent features indeed to alien astronomers viewing our galaxy from positions in the Andromeda Galaxy. (Positions where they had a clear view of us.) They too have obscuring dust and matter to see through.
    It's true that we have trouble seeing our own galaxy's core, but remember, the bands of the Milky Way that we see are edge on too--in other words, we're seeing the effect of the stars of the entire disk--in some directions we're looking at concentrations of stars over 100,000 lightyears thick. If you were to look at the Milky Way from outside, from perpendicular to the disk rather than edge on, the thickness of the Milky Way would be a magnitude less.

  23. #53
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    After reading thru all the posts on this subject, GrapesOfWrath just stole my thunder with his last post. However, I won't let that keep me from making my comments.

    Using Mr. Schwarz's example of viewing the Milky Way at a point 64,000 lys above the center;

    1) With the exception of a center that is not blocked by dust, the stars generally won't be any brighter than we see them now.

    2) With approx. 1/10 the density of stars to look at (because you are now looking at it from a point perpendicular to the plane of the galaxy), I think you would have trouble picking out the spiral arms of the galaxy from the background stars.


    Do you have a link to the Jay Ryan cartoon?

    Thanks.

  24. #54
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    No, they've taken them offline, I believe. At least, the links that I used to have at Sky and Telescope are no longer effective.

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    I just got the latest BA newsletter and he links to his explanation of how he wrote the article for Astronomy Magazine. It seems he's considering the example of looking at the Milky Way from 100,000 lightyears from the disk. I still haven't seen the article itself, but I'll be interested in the reactions. Which objects did he discuss? He seemed to include a globular cluster and the Orion Nebula.

  26. #56
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    And, I just retrieved the Timothy Ferris book Seeing in the Dark off the library shelves last week. I highly recommend it.

    He discusses the view of the Tarantula nebula through the telescope at Las Campanas Observatory on page 50. He describes it as "bright enough to make me squint." Still, we'd have to do the math to figure out what that nebula would look like from up close...

    I'll be back in a few hours. [img]/phpBB/images/smiles/icon_smile.gif[/img]

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