The way we perceive space; the difference between telescope

[A Song Of Distant Earth]

I'm doing some research about space and astronomy, and I'd like to find an answer to a question that has bugged me for ages now. For the longest time I had no idea where to look for answers, but since I accidentally stumbled across the Bad Astronomer's page recently and spent many hours hence glued to the screen while perusing his site I believe I may finally have found a good place to start. At first I wanted to write to the BA himself, but when I noticed a piece of text on the site that said it could take him up to a month or more to reply to emails due to the amount of mail he receives, I decided to check out the forum instead and was happy to find a thriving community filled with people whose passion for the cosmos is equally great. So I hope I will find my answers here [img]/phpBB/images/smiles/icon_smile.gif[/img]

My question in itself is actually quite simple, but it's a little hard to explain it properly. Essentially I'd like to know whether there is a great difference between how we see cosmic vistas such as nebulae through sophisticated telescopes and how we would see them with our own eyes from certain points in space. I realize this is still pretty vague, so let me try to clarify a bit with a picture:
http://www.seds.org/billa/twn/img/ant.jpg
None can deny the inherent beauty of such images, and I'm sure many here, like myself, have spent many an hour gazing at the pictures the HST has made since its launch. What I always wondered about though is how these vistas would be seen by us humans. In the above pic for instance, we see in the top left hand corner the supergiant Antares. Around it are several more stars (the blue on on the right is Rho Ophiuchi, I don't know the names of the other ones), each illuminating great clouds of material around them with their light. But while I love to see pix like these, I can't help but doubt that such things can actually be seen without the magnifying effect of a powerful telescope. The stars in the picture for instance almost appear to be right next to each other, while I'm sure that, like with any other stars, quite a few lightyears lie between them. This would mean that if you were to find yourself within the Antares system, the other stars in this picture would probably look no different from the way we see stars from within our own system; merely as tiny specks of light and nothing more. Another example I'll bring up is something I suppose everyone is familiar with: the closing scenes of The Empire Strikes Back. There we see Luke Skywalker, Princess Leia and the robots standing in front of a large window on a frigate, staring into space. What they see is a great galaxy (I think it was a galaxy at least; it's been a while since I last saw the movie), rotating slowly. A similar scene is to be seen near the end of the movie 'Contact'. Now I wonder how realistic such scenes are; can one really see a galaxy in that way from certain points in space, spread out before one's feet like a giant, rotating wheel of stars? The more I think about it the more implausible it seems. The reason I put this as an example is because Contact has been reviewed on the Bad Astronomy site, and nothing was said about it; perhaps it was only an oversight, but I reckon that if such a scene is truly impossible, then the Bad Astronomer would probably have mentioned it in his review. He didn't however, so again I'm in doubt. The same train of thought can be used when it comes to nebulae; can one really look through the window of a spaceship, or look up at the sky from the surface of a hypothetical planet, moon or asteroid, and see massive, colourful nebulae that are lightyears across, like one might see in a fantasy/sci-fi painting, or are such things confined only to the minds and works of the artists who make them? I also wonder how it would be to actually be inside a nebula; would you actually notice, like it was depicted in the PC game Freespace II? If not, what would it be like in reality? In the picture of Antares, too, there are large clouds of gas or dust to be seen around the stars, but would you see them with your own eyes if you were to be in orbit around any of them, or would things look fairly similar to our own solar system, and are the clouds we see merely visible due to the greater sensitivity (when compared to the sensitivity of the human eye) of the telescope that was used to photograph them?

I hope my inquiries are clear; as I said I'm having kind of a hard time describing exactly what I mean. Also I realize that since man has only waded a few steps in the galactic waters (and has therefore not had the opportunity - yet - to see for himself what the naked eye may or may not perceive from any given point in space), it's likely these issues are debatable. I'll say here and now that I know very little of such matters myself, and while I try to learn everything I can about the universe around me my knowledge is no doubt far surpassed by the majority of the people on this forum (judging by what I've seen while perusing these boards for a few minutes). If you choose to answer my post however, I beg you to keep the math down to a minimum should you feel the need to use it, since I'm afraid it and myself can never be anything else then sworn enemies [img]/phpBB/images/smiles/icon_wink.gif[/img]

[Geo3gh]

On 2002-08-10 23:05, A Song Of Distant Earth wrote:
In the above pic for instance, we see in the top left hand corner the supergiant Antares. Around it are several more stars (the blue on on the right is Rho Ophiuchi, I don't know the names of the other ones), each illuminating great clouds of material around them with their light. But while I love to see pix like these, I can't help but doubt that such things can actually be seen without the magnifying effect of a powerful telescope. The stars in the picture for instance almost appear to be right next to each other, while I'm sure that, like with any other stars, quite a few lightyears lie between them. This would mean that if you were to find yourself within the Antares system, the other stars in this picture would probably look no different from the way we see stars from within our own system; merely as tiny specks of light and nothing more.

Quite right. As an example, let's take our own sun. If you were standing on Pluto, you'd see our sun as a bright star. And that's only 40 AU away. Six ten-thousandths of a light-year. At even a couple of light years of distance, it's all just points of light.

Another example I'll bring up is something I suppose everyone is familiar with: the closing scenes of The Empire Strikes Back. There we see Luke Skywalker, Princess Leia and the robots standing in front of a large window on a frigate, staring into space. What they see is a great galaxy (I think it was a galaxy at least; it's been a while since I last saw the movie), rotating slowly. A similar scene is to be seen near the end of the movie 'Contact'. Now I wonder how realistic such scenes are; can one really see a galaxy in that way from certain points in space, spread out before one's feet like a giant, rotating wheel of stars?

Well, you wouldn't see it actually rotating. It's not moving that fast to be seen moving at that distance. But there are points in space where you could see the Milky Way, for example, sprawled out before you, taking up your entire field of vision.

(I'll have to bring your sworn enemy in here, I'm afraid.)

Let's say you want to have the Milky Way take up a 90 degree swath of the sky. Not your entire field of vision, but pretty darn big.

It's simple geometry. The Milky Way is 100,000 ly in diameter. We need to convert the 90 degrees to radians for the formula. 90 deg = pi/2 radians.

s = r*theta

where
theta = the angle the Milky Way subtends (in this case pi/2)
r = the distance to the Milky Way (how far away we want to be)
s = the arc length (in this case the Milky Way's diameter: 100,000 ly)

so we want to find r

r = s/theta

r = (2*100,000 ly)/pi
r = (roughly) 64,000 ly

At 64,000 light years above the Milky Way, it would take up 90 degrees of the sky. A big beautiful, static image.

Now, the only problem is getting there. *Sigh.*



_________________
Jeff Schwarz
__________________________________________________
I have Invader's blood marching through my veins
like giant radioactive rubber pants! The pants
command me! Do not ignore my veins!
--Invader ZIM

<font size=-1>[ This Message was edited by: Geo3gh on 2002-08-11 00:17 ]</font>

[Firefox]

According to the effects supervisors, the object in question was actually a nebula. Of course it looked like a galaxy to me.


-Adam

[Chip]

Hello "A Song Of Distant Earth!" These are great questions and I'd like to have an initial go at them. Other folks might jump in with more details.

A.S.O.D.E.:
"...At first I wanted to write to the BA himself, but when I noticed a piece of text on the site that said it could take him up to a month or more to reply to emails due..."

Chip:
Hang in there! I've noticed that he checks up on the shenanigans here, so he may spot your questions and offer some answers. (He worked on some cool Hubble Space Telescope projects, and knows people who work directly with that telescope, so he'll offer some direct insights most of us don't have!)

A.S.O.D.E.:
"...I'd like to know whether there is a great difference between how we see cosmic vistas such as nebulae through sophisticated telescopes and how we would see them with our own eyes from certain points in space."

Chip:
Yes and no. Often times astronomers will photograph distant objects such as nebula or galaxies either in specific wave lengths, such as X-rays. They look at the sun for example in hydrogen light or through different filters to reveal different details. Other times they deliberately color nebula in "false colors" to bring out specific details they want to see. Usually these are identified as such in good journals and books. Other times they actually try to get a picture that reveals what a nebula would look like to human eyes if we were closer. The Crab Nebula is one of many that has been photographed this way.

A.S.O.D.E.:
...the pictures the HST has made since its launch. What I always wondered about though is how these vistas would be seen by us humans."

Chip:
Even in the best amateur astronomer's earth bound telescope under excellent seeing conditions, almost all the nebulas look like faint gray fuzzy clouds. (But no less thrilling to see with your own eyes!) The reason for this might surprise you. Our eyes are not sensitive to colors below a certain threshold of brightness. So we see in black & white. One can see faint colors in the Orion Nebula under the best seeing conditions, but to answer your question, yes, many of those wonderful nebulas really are in vivid colors to the human eye if we were closer.

There is also the matter of perspective which you touched on...

A.S.O.D.E.:
"...The stars in the picture for instance almost appear to be right next to each other, while I'm sure that, like with any other stars, quite a few light-years lie between them. This would mean that if you were to find yourself within the Antares system, the other stars in this picture would probably look no different from the way we see stars from within our own system; merely as tiny specks of light and nothing more."

Chip:
I think you are essentially correct. In many pictures of open star clusters it appears that the stars are almost "rubbing shoulders" but if you were on an earth-like planet going around one of them, the other stars would be points of light in your night sky. Space is very very big. We see the cluster from far far away, so we see it as a whole. Nevertheless, space has a lot of wondrous variety, and there are also binary systems that are extremely close together. If we were there, we'd have two suns and a weird orbit! Also, if we were deep inside Globular clusters, our night sky would be very spectacular indeed, if not dangerous! If we were a bit further out and a bit "above" the Milky Way, we'd see the the spiral shape fill the night sky in a more recognizable way. We're deeper within it and have to contend with interstellar dust lanes and a seemingly irregular shape. Also, in star photographs we get "a forced perspective" which places stars close together, though one may be considerably further away but "just to the east" of the other star. We can't tell just with our eyes because they're both bright points of light. If you've ever seen a picture of an airplane flying in front of the full moon, and the plane fills the moon's diameter, that's a forced perspective image. The plane would be invisible if it were actually sitting on the moon's surface, but the moon is much further away. Same with many stars. (Yet some stars are really close together too!)

A.S.O.D.E.:
"...the closing scenes of The Empire Strikes Back...we see...a great galaxy ...rotating slowly. A similar scene is to be seen near the end of the movie 'Contact'. Now I wonder how realistic such scenes are; can one really see a galaxy in that way from certain points in space, spread out before one's feet like a giant, rotating wheel of stars? The more I think about it the more implausible it seems.

Chip:
Again, yes and no. Though I personally haven't been to the outer rim of the Milky Way yet, I'm pretty sure that somebody somewhere has that view! Just imagine backing away from the Milky Way until you see the spiral shape ( some astronomer's think its a "barred spiral" by the way, which the movies don't show.) However, we can't see the rotation with our eyes. Unless we stand there a very very very long time. In human (or robot) terms, galaxies are way to big for rotation to be physically seen in one's lifetime. However, rotation can be detected with instruments using red-shifts of the spiral arms.

A.S.O.D.E.:
"...The same train of thought can be used when it comes to nebulae; can one really look through the window of a spaceship, or look up at the sky from the surface of a hypothetical planet, moon or asteroid, and see massive, colorful nebulae that are light-years across, like one might see in a fantasy/sci-fi painting, or are such things confined only to the minds and works of the artists who make them?"

Chip:
That's a very good question! There are some who might disagree with me, but I'll stick my neck out and say; Yes! (But not under every circumstance.) (1.)There are actually nebulas that are quite colorful, bright, and spectacular in the frequencies that the human eye can see. (2.) If we were in the right spot, not too far, and not within the nebula or too close, we would see it bigger and brighter, and it would fill the sky as artists depict it. (3.)This is not always true. Some huge nebulas are very faint even if you were only 1/100th of a light year away, and they would be all but invisible to human eyes even up close without long time exposures. Others would be bright enough to fill the sky, but faint enough to remain gray and dim to human eyes. However, if a nebula has bright young super giant stars in or near it, its gasses will glow more brightly. So yes and no.

A.S.O.D.E.:
I also wonder how it would be to actually be inside a nebula; would you actually notice, like it was depicted in the PC game Freespace II? If not, what would it be like in reality?

Chip:
By way of analogy, when I was a kid in Arizona, we'd sometimes get massive desert dust storms. We felt like Martian colonists! The storm would approach like a wall of red dust. But when it actually hit, it would be much lighter than expected, though we'd suddenly notice fine grit everywhere and even in our teeth! Other times, dust storms were just like the movies - wild and thick. I think by and large, defuse nebulas would be harder for human eyes to see if we were inside them. Denser nebulas would be spectacular up close. Some dark clouds would blot out all the stars if we were inside them. Space is big and strange.

A.S.O.D.E.:
In the picture of Antares, too, there are large clouds of gas or dust to be seen around the stars, but would you see them with your own eyes if you were to be in orbit around any of them, or would things look fairly similar to our own solar system, and are the clouds we see merely visible due to the greater sensitivity (when compared to the sensitivity of the human eye) of the telescope that was used to photograph them?

Chip:
Distance and camera sensitivity are important factors, plus time exposures. Again, there are some areas of star formation within massive dense nebula that would be tremendously impressive up close, and there are nebulas that are thin and faint from any distance (by human standards.) Our solar system is actually located in a region called "the local bubble" of hot gasses -- about 300 light years in diameter. Its from a 10 million year old super nova. Human eyes can't see it. Alien scientists far from us - if they had the same equipment ways of detecting such things, would "see" the "bubble". There's a space mission coming up called (CHIPS) (no, they didn't name it after me,) that will study this gas. On the other hand, in other parts of the galaxy, if we were just in the right place, close but just outside the Crab Nebula, we's see it in the sky, in color, without binoculars! Reason: It's bright and emits light also in the spectrum that human eyes can see.

One other thought - I sometimes hear people say those old 1950's Chesley Bonestell paintings of moonscapes are wrong, because the Apollo pictures show a much smoother surface with rolling hills and usually smaller rocks. But Bonestell got to look at the moon through excellent telescopes from time to time, as an artist he went for the most stunning views, and lo and behold, there actually are places on the moon with tall pointed, jagged peaks and spectacular canyons. However, the Apollo astronauts didn't land there. It was dangerous enough landing where they did. (In fact, Neil Armstrong just missed a pile a boulders seconds before the first landing.) Also, if the terrain is that jagged with a resolution kilometers across, then it's most likely very jagged on the smaller scale of humans and the LEM.
I hope this answers some of your questions. Space is grand!

[nebularain]

Welcome to the Board A Song of Distant Earth! (Cool name by the way [img]/phpBB/images/smiles/icon_cool.gif[/img] .)

Very thoughtful questions you have there. I'll give my best shot at what I can. [img]/phpBB/images/smiles/icon_confused.gif[/img]

[Edit: Chip beat me to the post (!) so some of these are repeated re-wordings of what he said.]

Easy one first: seeing the rotating galaxy out the window. The BA mentions the ability (or rather inability to see stars out the window in his review of Enterprise (TV review section). Basically, the light inside the room would inhibit a person's ability to see stars out through the window. So the window would actually look dark, just like it does for you at home. Now, suppose there were absolutely no internal light, I don't know how it would work for such large windows, but I do know at home I can see some of the brighter stars if I get close enough to the window at the correct angles (of course, I live in a suburban area; don't know how the country view would go). So, you can juggle those ideas around. As per the rotating galaxy, well if you could see the galaxy through the window, if you were at at the correct distance you could see the whole thing as it showed in the movie (the bottom line of all the math figures mentioned in a oprevious post). But I doubt you would actually see the movement of rotation. Although we have been able to calculate stellar objects moving at very high velocities, due to the distance of view we most likely could not see it. (Have you ever noticed planes flying overhead? Well, I live under an airport flight path so I can see this. The airplanes higher in the atmosphere appear to move slower than those that are lower, that is the ones taking off or landing. It's the same idea. Far enough away, as in space, motion appears to stop.) At the distance the craft needs to be to view the entire galaxy, I believe they would be at such a distance.

Telescope versus naked eye images. Since telescopes merely magnify images, as far as I know, if we were close enough the view should be the same (like view through binoculars). But this would only apply for those images taken in the visible spectrum of light. Many images we have pictures of are "false color" images; that is, color was added for viewing clarity. They do this with infrared, x-ray, etc. images. I can't recall any false color added to visible light images, but I could be wrong.

How would a nebula look from the inside? I don't know. I remember having read somewhere that closer up the dust cloud would not seem as thick, but I can't remember where I saw that. Hopefully, someone else will have a better idea. The best I can say is to notice how many light years across it is mentioned that the imaged nebula is and imagine the possibilities of how far the dust grains could be from one another - my guess is that they are pretty far apart. So it is possible you may see things through a haze at best if you were inside it. Color, though, I'm not sure enough about to blab about.

Hope this helps, and I hope I'm correct! [img]/phpBB/images/smiles/icon_wink.gif[/img]

And BTW, if you haven't found it yet, a really awesome astronomy website is the "Astronomy Picture of the Day":
http://antwrp.gsfc.nasa.gov/apod/archivepix.html .
_________________
"All that is gold does not glitter / Not all those who wander are lost..."

<font size=-1>[ This Message was edited by: nebularain on 2002-08-11 02:17 ]</font>

[GrapesOfWrath]

On 2002-08-11 01:35, Chip wrote:
One can see faint colors in the Orion Nebula under the best seeing conditions, but to answer your question, yes, many of those wonderful nebulas really are in vivid colors to the human eye if we were closer.

We had a little discussion about this earlier, in the thread Outside view of the Milky Way.

The Sky and Telescope feature that I mention is a cartoon by Jay Ryan, I think, although I can't remember the issue. 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.

[xriso]

Relating to the topic of getting closer to an astronomical object... if one were to half the distance to a nebula, then you are recieving 4 times the light (inverse-square law), but at the same time the object appears 4 times bigger (double both dimensions). Conclusion: It doesn't get any brighter since the brightness-density is the same. Is this logic correct?

Obviously this doesn't apply to point-like sources of light, such as distant stars, perhaps because all the light we see from the star is being poured into one pixel.

<font size=-1>[ This Message was edited by: xriso on 2002-08-11 06:01 ]</font>

[GrapesOfWrath]

xriso

Essentially, that was Jay Ryan's point, I think.

When we look at a patch of the Milky Way, it's bigger than any other galaxy, but is about as bright, on a per square arcsecond basis.

[Kaptain K]

One point that hasn't been made is difference in dynamic "scale" between vision and imaging. Photographs (whether film or CCD) are essentially linear in their response. Double the number of photons, double the image density. The response of the human eye is logarithmic. It takes more than double the number of photons to perceive a doubling in brightness. This compresses the dynamic range to a level that the brain can deal with effectively. So, astrophotos do not "look" exactly like the object would appear to the eye. A good example is M42 (the Orion nebula). We have all seen gorgeous photos showing tremendou streamers and tendrils extending out from a badly over exposed central region where the stars that are exciting the nebula to glow are. A photo with a short enough exposure to show these stars (known as the Trapezium) will barely show any of the nebulosity. Look at M42 through a telescope and you will see both the stars and the nebulosity. Another difference is in color sensitivity. Photos of M42 will show the nebulosity to be mostly red and blue. To the human eye through a scope, it is very definitely green. Through larger scopes, hints of the reds and blues can be seen, but green still dominates. This is due to the eye's greater sensitivity in that region.

_________________
When all is said and done - sit down and shut up!

<font size=-1>[ This Message was edited by: Kaptain K on 2002-08-11 08:44 ]</font>

[Chip]

On 2002-08-11 04:58, GrapesOfWrath wrote:
We had a little discussion about this earlier, in the thread Outside view of the Milky Way. The Sky and Telescope feature that I mention is a cartoon by Jay Ryan, I think, although I can't remember the issue. Basically, he points out that spectacular closer-up views of galaxies are a result of artistic license only.

I read the Jay Ryan cartoon too and thought it was quite well done. I also contributed to the BABB thread you linked to. But I stand by what I wrote here. The Milky Way example has to do with backing away from a large celestial object. In the part you quoted in this thread I'm talking about hypothetically getting physically closer to nebulas. If we were at a location that was just right, some nebulas would be brighter to the human eye. (Jay Ryan also drew them that way.) Telescopes don't move closer but they do magnify the image, and in some cases, astronomers reproduce images that mimic what the human eye would see if it were closer. Secondly, not all nebulas are the same intrinsic brightness. Some are much more luminous than others.

[Chip]

On 2002-08-11 06:00, xriso wrote:
Relating to the topic of getting closer to an astronomical object... if one were to half the distance to a nebula, then you are receiving 4 times the light (inverse-square law), but at the same time the object appears 4 times bigger (double both dimensions). Conclusion: It doesn't get any brighter since the brightness-density is the same. Is this logic correct?

Logical in theory, but not quite right in practice. Actual nebulas are not all the same brightness, and differ greatly from one another. The stellar nurseries have young bright stars within or near them that excite the gasses to a brighter luminescence, within the range of the human eye. "Planetary nebulas," which are the remains of novae and haven't re-condensed into recycled stars, would probably be faint or even dimmer up close and within. As implied by the approaching "dust storm" analogy I used.

[David Hall]

Hi, A.S.O.D.E., Welcome aboard.

1: Cameras have an ability the eye lacks, they can collect light over time. The image we get in our eyes is being constantly refreshed, and therefore we are limited in our ability to see faint objects. But camera film builds up a picture over time by collecting more and more photons, so very faint objects can become brighter and clearer. It can be a disadvantage with brighter objects though. If you image a bright star for example, after a while the film can't absorb any more photons and the reaction starts to bleed out into the surrounding medium. Therefore stars can often seem much larger on an image than the pinpoints they really are. Fortunately, modern CCD's are less affected by this, so the image quality is getting better.

2: Looking up at the Milky Way from the Earth, all we see is a band of light that's slightly brighter than the background. Using xriso's idea that surface brightness wouldn't vary with distance, and we can guess that, even if we were in a position to see more of the galactic disk, it would still appear as that same slightly brighter patch in the sky. The shape would be different though, it would be a diffuse spiral in the sky instead of a band. The galactic core would probably be impressively bright, however as we'd be out of the way of the dust lanes that are blocking it from sight now. It's much brighter intrinsically than the spiral arms.

3: From the outside, nebulae seem very solidly packed, like the clouds we see in the sky, but in reality they are very very diffuse and the individual particles are quite far from each other, like in Chip's dust storm analogy. From outside they might look very impressive, depending on what kind of illumination they are getting, either reflection from neighboring stars, or internal emmision from infrared heating by stars inside it. Inside a nebula though you wouldn't really notice anything, except that the sky around you would be unusually devoid of stars. Some SF authors (Asimov especially comes to mind) have used this in their stories. From outside the nebula you can't see a particular system, but once you get inside, the nebula does not hinder you in any way. It's only when you have to look through great masses of dust that it noticably starts blocking light.

4: I think the spiral shape at the end of TESB is supposed to be a protoplanetary system, a young star surrounded by a disk of nebulous material in the process of forming planets. It would have been nice if they had made it look a little less galaxy-like at the end of the movie though, as it does seem to imply that they are outside of the galactic disk. But when the Falcon leaves them, it doesn't head towards the swirl, but off to one corner of the screen, which is one small clue that it's not the galaxy itself. Also, the background behind the nebula is still full of stars, which wouldn't be the case if they were outside of the galaxy.

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<font size="-1">PLEASE NOTE: Some quantum physics theories suggest that when the consumer is not directly observing this product, it may cease to exist or will exist only in a vague and undetermined state.</font>

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<font size=-1>[ This Message was edited by: David Hall on 2002-08-12 04:48 ]</font>

[David Hall]

On 2002-08-11 17:23, Chip wrote:

Logical in theory, but not quite right in practice. Actual nebulas are not all the same brightness, and differ greatly from one another.

This is only important when comparing one nebula to another. But each one on it's own still obeys the inverse-square law. If you move away from any nebula the surface brightness of that nebula would remain the same as distance increases.

[Argos]

On 2002-08-11 00:16, Geo3gh wrote:

At 64,000 light years above the Milky Way, it would take up 90 degrees of the sky. A big beautiful, static image.

Now, the only problem is getting there. *Sigh.*

I guess it would require a great deal of energy to get to 64 kly, having all the galaxy's mass pulling the ship back.

I just wonder *why* to get there; to be suspended amidst the intergalactic space, far away from any star. Only a desperate need for a hiding place would justify the enterprise.

I suspect that no human eye will ever behold a 90 degree view of a galaxy.

[nebularain]

Wow! I'm glad A.S.O.D.E. asked her questions; I myself been learning a lot reading these posts.

I do wish, though, there was a way we could send a probe above the galactic plane. Wouldn't that be cool to actually have a real picture of our own galaxy!

[Chip]

On 2002-08-12 13:43, nebularain wrote:
"...I do wish, though, there was a way we could send a probe above the galactic plane. Wouldn't that be cool to actually have a real picture of our own galaxy!

"An image of the Milky Way Galaxy taken from earth orbit in the infrared." Source: http://isaac.exploratorium.edu/~paul...esizeillo.html

"This equal-area projection of the three-color composite JHKs source count map of the entire sky shows 95,851,173 stars of magnitude 13.5 or brighter in Ks (2.2 µm) infrared light. The Milky Way Galaxy, laced with dark dust lanes and clouds, and its bright core are at center. The Large and Small Magellanic Clouds, nearby satellite galaxies of the Milky Way, look like smudges below the galactic plane. The source generation was performed by M.F. Skrutskie (UMass), the flux maps were compiled by J.M. Carpenter (Caltech), and the color composite was assembled by R. Hurt (IPAC/Caltech)." Source: http://www.npaci.edu/envision/ v17.3/heavens.html <http://www.npaci.edu/envision/v17.3/heavens.html>

<font size=-1>[ This Message was edited by: Chip on 2002-08-12 15:39 ]</font>

[GrapesOfWrath]

On 2002-08-12 15:33, Chip wrote:
"An image of the Milky Way Galaxy taken from earth orbit in the infrared."

Ah. See, that is what the Milky Way looks like close up. Looks a lot like pictures we see of other galaxies. But, even close up, it doesn't look as near as spectacular as the photos. It wouldn't look much different if we were a bit farther away--smaller, but the surface brightness stays about the same.

[nebularain]

Cool pics Chip! But I was thinking of an outide-of-the-galaxy shot; kind-of like we can see the Andromeda galaxy; you know, where we can see the bar and the spiral arms and how they are spaced and such.

[Chip]

On 2002-08-12 15:47, GrapesOfWrath wrote:
"Ah. See, that is what the Milky Way looks like close up. Looks a lot like pictures we see of other galaxies. But, even close up, it doesn't look as near as spectacular as the photos. It wouldn't look much different if we were a bit farther away--smaller, but the surface brightness stays about the same.

With all due respect, your point is meaningless to me. In infrared, or even within the limited range of human vision, it looks just breathtaking to me.

[Chip]

On 2002-08-12 16:00, nebularain wrote:
Cool pics Chip! But I was thinking of an outside-of-the-galaxy shot; kind-of like we can see the Andromeda galaxy; you know, where we can see the bar and the spiral arms and how they are spaced and such.

Oh, for that we'll have to wait for one of Dr. Phil Plait's offspring to invent warp drive. [img]/phpBB/images/smiles/icon_wink.gif[/img]

[GrapesOfWrath]

On 2002-08-12 16:28, Chip wrote:
With all due respect, your point is meaningless to me. In infrared, or even within the limited range of human vision, it looks just breathtaking to me.

Are you talking about the images you posted, or the naked-eye view? OK, I see it can't be the naked-eye view--you mention infrared--but the naked eye view is what the OP was asking about.

I think the Milky Way is spectacular too, as it is, but it is nothing like the photos, and apparently wouldn't be, no matter how far or close we were.

[Gsquare]

Excellent pics, Chip. Quite a shot. Impressed; even the SMC & LMC in the 2nd one.

I think I even see some 'missing' mass. [img]/phpBB/images/smiles/icon_biggrin.gif[/img]
G^2

<font size=-1>[ This Message was edited by: Gsquare on 2002-08-12 23:53 ]</font>

[Chip]

Grapes of Wrath wrote:
"I think the Milky Way is spectacular too, as it is, but it is nothing like the photos, and apparently wouldn't be, no matter how far or close we were."

Chip:
I think we're (you and I) mixing an applied scientifically measurable intrinsic brightness, with a subjective or aesthetic impression of brightness. (Brightness that is variable - especially if, as was pointed out, one turns the interior lights out in the starship's observation lounge!) Again, I was mostly writing about nebulas within our galaxy being seen much closer, rather than from farther away. Some nebulas are brighter than others, and some nebulas do look very similar to those photos where scientists are deliberately trying to capture a "human's eye view" in terms of accurate colors.

Out in the Arizona desert, Australian outback, and quite a few other remote areas (when the sky cooperates) the Milky Way is unbelievably clear, detailed, and very very similar to some photos (not the infrared composite ones I posted.) Those composites give you an idea of what the Milky Way would look like from outside the galaxy seen edge on. If we were located in such a position that the Milky Way (or many other galaxies to choose from,) "filled" our night sky from an outside viewpoint that revealed the spiral structure, we'd see the details, and in some cases we'd see a view similar to the photos created to mimic the human eye. Of course longer exposures can gather more light than the human eye is going to see, but that doesn't mean that a galaxy will be equally dim from any direction and never "look like the photos." How do I know? I've seen the Milky Way as it is viewed from right here on Earth - from a remote area on a very clear night, and even though it's brightness might be measurably the same as other positions in space, it can be remarkably similar to the photos. The area around Scorpius is particularly bright. Despite what the Sky & Telescope cartoon said, the human eye could detect colors in space if we're close enough - in some cases.

<font size=-1>[ This Message was edited by: Chip on 2002-08-13 04:14 ]</font>

[GrapesOfWrath]

I've seen colors from space--that's why they call it Antares, right?

Regardless, we're talking about the Milky Way, as a galaxy. I too have seen it from remote locations, I was born and raised in Wyoming, but the night sky on Earth cannot approach the view shown in your images, naked-eye. Your caption points out that it shows stars to 13.5 magnitude--the usual cutoff for naked-eye observation is 6.5 (although we've had some discussion here, and the BA has mentioned, some reports of up to 8.5, with averted vision maybe), so that means the images are 100 times brighter at least.

[Chip]

GrapesOfWrath:
Regardless, we're talking about the Milky Way, as a galaxy. I too have seen it from remote locations, I was born and raised in Wyoming, but the night sky on Earth cannot approach the view shown in your images, naked-eye.

Chip:
I didn't say they did. Those images I found on the internet in response to Nebularain's wish to see the Milky Way from further out in space. Except perhaps for the shape, they have little to do with how the Milky Way would look to human eyes from a greater distance away, (but still close enough to see the spiral shape.) The point is: from some other vantage point, you could see the spiral shape. You can see the Andromeda galaxy with the naked eye. If you were physically closer, you'd see more of it.

GrapesOfWrath:
Your caption points out that it shows stars to 13.5 magnitude--the usual cutoff for naked-eye observation is 6.5 (although we've had some discussion here, and the BA has mentioned, some reports of up to 8.5, with averted vision maybe), so that means the images are 100 times brighter at least.

Chip:
Small point: It's not my caption, that's why I put it in quotes and linked to the source. Big point: I did not say that those images are what one sees with the naked eye.

As per galaxies, "A Song of Distant Earth" asked "...can one really see a galaxy in that way from certain points in space?" I wrote: "Again, yes and no...I'm pretty sure that somebody somewhere has that view! Just imagine backing away from the Milky Way until you see the spiral shape."[/i]

Then the subject switched to nebulas. (Long ago, Galaxies were also called "nebulas," but the definition is different these days.)

[The Bad Astronomer]

I'm afraid I don't have time to go into a lot of details here... but a nebula uip close might be a bit disappointing. The diffuse emission from a nebula gets spread out over the whole sky, making it look so faint you cannot see it. Filaments and streamers would be bright, though.

I will say simply to wait until the January issue of Astronomy Magazine. There will be a longish feature article about this very topic. It's illustrated by Lynette Cook, an extrmemely accomplished space artist, and talks about close-up views of a nebula, a red dwarf star and a globular cluster. I hear the author has a really good website too. [img]/phpBB/images/smiles/icon_wink.gif[/img]

[GrapesOfWrath]

On 2002-08-13 13:44, Chip wrote:
I didn't say they did.

Sorry. I thought that was what you meant when you said "If we were located in such a position that the Milky Way (or many other galaxies to choose from,) "filled" our night sky from an outside viewpoint that revealed the spiral structure, we'd see the details, and in some cases we'd see a view similar to the photos created to mimic the human eye."

Which photos are you talking about then?

You can see the Andromeda galaxy with the naked eye. If you were physically closer, you'd see more of it.

Not more of it, but it would appear to be larger. The point is, it wouldn't be brighter, on a per area basis.

Big point: I did not say that those images are what one sees with the naked eye.

I did notice that the captions said they were infrared.

As per galaxies, "A Song of Distant Earth" asked "...can one really see a galaxy in that way from certain points in space?" I wrote: "Again, yes and no...I'm pretty sure that somebody somewhere has that view!

I'm pretty sure not, but I guess you've said you disagree with Jay Ryan, there.

Just imagine backing away from the Milky Way until you see the spiral shape.

The issue is not one of perspective--it's one of how bright the image would appear to the observer.

[Chip]

On 2002-08-13 16:26, GrapesOfWrath wrote:
The issue is not one of perspective--it's one of how bright the image would appear to the observer.

Sigh...Well, I guess I'll just have to muddle along in my illusion that (in theory, since we can't go there,) the closer we are physically are to a galaxy made up of the combined luminescence of billions of stars, regardless of how intrinsically bright or dim it remains, (and it remains at the same level,) the more details we'll tend see as we get closer. (I think we'll see more details even though the brightness remains the same.) Why? Structures within it that were far away are larger to us now - regardless of the fact that they are at the same light level. The further away from it we physically are, the less details we'll see regardless of intrinsic brightness. ("Intrinsic" i.e. luminescence inherent to the object.) This is mimicked in the telescope, which magnifies the distant object, and brings out details the naked eye didn't resolve. Planetary nebulas on the other hand would probably become dimmer as we approached them up close. Their level of luminosity as seen from a distance being dependent on the combined effect of large areas of thin glowing gas. Stellar nurseries such as the Orion nebula, if seen naked eye, up close, would probably tend to be intrinsically brighter than other nebulas. We see more detail magnified or physically up close, than we do far away. Perspective is a factor. That's my opinion.

[David Hall]

On 2002-08-13 17:44, Chip wrote:

Sigh...Well, I guess I'll just have to muddle along in my illusion that (in theory, since we can't go there,) the closer we are physically are to a galaxy made up of the combined luminescence of billions of stars, regardless of how intrinsically bright or dim it remains, (and it remains at the same level,) the more details we'll tend see as we get closer. (I think we'll see more details even though the brightness remains the same.)

That's a good point. I think we can agree on that one. The closer you get, certainly the more detail you'll be able to see. More clusters, nebulae, structures, and individual stars will be visible. It's just that the overall brightness will remain about the same.

[GrapesOfWrath]

On 2002-08-14 05:46, David Hall wrote:
I think we can agree on that one.

I agree on that one, too. No need to muddle. [img]/phpBB/images/smiles/icon_smile.gif[/img]