# Could the "visible light" images of some galaxies look the same to us as the Hubble? **URL:** \ **Category:** Factual Questions\ **Created:** [July 14, 2017, 3:54pm UTC](https://boards.straightdope.com/t/could-the-visible-light-images-of-some-galaxies-look-the-same-to-us-as-the-hubble/791256 "2017-07-14T15:54:15Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [July 17, 2017, 1:50pm UTC](https://boards.straightdope.com/t/could-the-visible-light-images-of-some-galaxies-look-the-same-to-us-as-the-hubble/791256/21 "2017-07-17T13:50:07Z")
> [@DesertDog](#): > > I’m not grasping what you mean by “the intensity is covering a larger area.” All I know is, when I tried my Carson City experiment mentioned in my first post I could see more objects in the night glasses than the day glasses, even though the magnification was less. With a 12-inch [Dobsonian](https://en.wikipedia.org/wiki/Dobsonian_telescope) there would have been even more. They’re called “light buckets” for a reason. When we’re talking about extended objects (galaxies and nebulae), telescopes help by enlarging objects that are too small to see with your naked eyes. A tiny dim blob becomes a huge dim blob. You’d want to use a magnification that gives you a large exit pupil (as large as your eye’s pupil), because if you use a higher magnification, you are turning a tiny dim blob into a huge _but even dimmer_ blob. It’s a little different for point sources (stars and perhaps small bright nebulae). You are still magnifying the image, but if a tiny unresolved dot becomes a larger but still unresolved dot, then you _are_ getting more light into one receptor in your eye. So a telescope allows you to see dimmer stars than you can with naked eyes. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [July 17, 2017, 2:29pm UTC](https://boards.straightdope.com/t/could-the-visible-light-images-of-some-galaxies-look-the-same-to-us-as-the-hubble/791256/22 "2017-07-17T14:29:31Z")
p.s. You could try for yourself - take a small telescope or binoculars and look at a nearby uniform surface (e.g. side of a building). Maybe look through it with one eye and open the other eye to look directly at it. The wall will be magnified in the telescope/binoculars, but it won’t look any brighter. ---
**Author:** ![DesertDog](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/desertdog/32/11503_2.png) [@DesertDog](https://boards.straightdope.com/u/DesertDog)\ **Post date:** [July 17, 2017, 4:49pm UTC](https://boards.straightdope.com/t/could-the-visible-light-images-of-some-galaxies-look-the-same-to-us-as-the-hubble/791256/23 "2017-07-17T16:49:49Z")
> [@Chronos](#): > > It’s easy to magnify an object while decreasing the surface brightness. That’s what you’ll get if you use too small an aperture. Use the proper size aperture, though, and you can magnify an object while maintaining the same, or very nearly the same, surface brightness. So the view through large-aperture binoculars will be brighter than the view through small-aperture binoculars. Neither will be brighter than the naked-eye view, but the naked-eye view might well be small enough (from lack of magnification) to not be useful. So the objects I could see through the glasses but not with the unaided eye was only because they were magnified with a proper-sized aperture? I’m not buying it; if magnification (with the proper aperture) was the only factor I’d still be able to see them unaided, just smaller. The Dobsons I linked to are large aperture, low magnification telescopes with the express purpose of looking at deep sky, dim objects. No advantage is gained over a smaller, easier to transport telescope in using them to look at the planets or the moon because there’s plenty of brightness anyway. In the Sky and Telescope article I linked to: > [@S&T](#): > > The bigger the aperture the better. With a 6-inch telescope you can discern craters on the Moon as small as about a mile across — half the size of those visible in a 3-inch scope (under the same conditions using the same magnification). The same two instruments turned toward a faint galaxy on a moonless night would tell an even more dramatic story. Because the surface area of a 6-inch mirror is _four times_ that of a 3-inch mirror, it collects four times as much light, meaning the galaxy would appear four times brighter. (Astronomically speaking, that’s 1.5 magnitudes brighter.) > > [Later, on magnification] > > When seeing a telescope for the first time, a novice will usually ask, “How much does it magnify?” The answer is, “Any amount you want.” Any telescope can provide an almost infinite range of magnifications, depending on the eyepiece you put into its eye end. > > But don’t get the idea that super-high powers will do you any good. Two main factors limit the power that shows a decent view with a given instrument: _aperture_ (again) and the _atmospheric conditions_. > > This is why observers generally use low powers for looking at faint things like galaxies and nebulae, and no more than medium-high powers for bright things like the Moon and planets. Just as enlarging a photograph too much will simply show you the grain in the film or the pixels on the chip, so too will excess magnification just make your target blurry. [Here](http://www.twcac.org/Tutorials/limiting_magnitude_table.htm) is a chart that shows what magnitude you can see with a particular aperture. Notice, magnification is not a factor considered. Obviously, it plays a part; otherwise peering through a toilet paper tube would magically make me see a 12-magnitude star I couldn’t see before. As I kind of said in my first post, magnification is what lets the light gathered by the larger aperture get shrunk down to an exit pupil that can get past the 7mm aperture of your eye. **scr4** , sorry for not answering your earlier reply to me just after **Chronos** , I missed it. > [@scr4](#): > > How is it not relevant? The question was whether any telescope could make a distant galaxy look as bright as it does in a Hubble photo. The correct answer is no, because no optical telescope can amplify the apparent surface brightness of an extended object. It follows from the laws of thermodynamics (if a telescope could amplify light, it would allow heat to flow from a colder object to a warmer object, which will reduce entropy.) > > Yes, I’ve heard many times that “a telescope is not a device for magnifying the view, it’s a device for collecting light.” > \ You got it right on the second part. True, a telescope doesn’t amplify light; it collects it through a larger aperture than your eye, then the magnification lets it fit through your eye’s aperture. Think of it this way. You’re looking at Sumdim Galaxy and 10,000 photons a second are getting to your retina, not enough to trigger the rods (never mind the cones). Now, you raise your 7x50 binos. Its aperture is 51 times that of your eye, collecting 510,000 photons a second all of which, thanks to the 7x magnification, are getting into your eye; now you can see it\*. Next you turn to your 10-inch Dobson which is gathering 2,030,000,000 photons a second. Anything above 25x magnification will let them all into your eye and, boy, can you see it; the more photons smacking your retina, the brighter it looks. Are the instruments amplifying the light? No, they are gathering it into a bunch and stuffing it into your eye. Does Sumdim _look_ brighter? You bet it does. > [@scr4](#): > > When we’re talking about extended objects (galaxies and nebulae), telescopes help by enlarging objects that are too small to see with your naked eyes. A tiny dim blob becomes a huge dim blob. You’d want to use a magnification that gives you a large exit pupil (as large as your eye’s pupil), because if you use a higher magnification, you are turning a tiny dim blob into a huge but even dimmer blob. See my parable above. > [@scr4](#): > > It’s a little different for point sources (stars and perhaps small bright nebulae). You are still magnifying the image, but if a tiny unresolved dot becomes a larger but still unresolved dot, then you are getting more light into one receptor in your eye. So a telescope allows you to see dimmer stars than you can with naked eyes. For all intents and purposes, stars _are_ point sources of light. Any enlargement you see of a magnified star is due to the [limitations](https://en.wikipedia.org/wiki/Diffraction-limited_system) of the optics, not the star’s disk getting larger. Otherwise, looking for exoplanets would have been a snap. Yes, we’ve been seeing some distant stars resolved into [disks](https://astrobob.areavoices.com/2014/06/06/can-we-really-see-other-stars-as-true-disks-you-betcha/), but that’s with equipment and image processing far beyond an amateur astronomer peering through her telescope, no matter what the aperture is. > [@scr4](#): > > You could try for yourself - take a small telescope or binoculars and look at a nearby uniform surface (e.g. side of a building). Maybe look through it with one eye and open the other eye to look directly at it. The wall will be magnified in the telescope/binoculars, but it won’t look any brighter. That’s right, it won’t because there’s plenty enough light that when you peer though the eyepiece, your iris contracts even further than it does when you’re gazing directly. I haven’t tried it, but I’d bet an exposure meter held up to the eyepiece would read higher than one aimed at the wall. When I go bird watching I take along the 8x35s rather than the 7x50s because there’s no advantage for the weight. \*I’m making the figures up; I have no idea how many photons a second constitute a magnitude 7 object, never mind getting into the whole wavicle thing. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [July 17, 2017, 5:48pm UTC](https://boards.straightdope.com/t/could-the-visible-light-images-of-some-galaxies-look-the-same-to-us-as-the-hubble/791256/24 "2017-07-17T17:48:17Z")
> [@DesertDog](#): > > looking at Sumdim Galaxy and 10,000 photons a second are getting to your retina, not enough to trigger the rods (never mind the cones). Now, you raise your 7x50 binos. Its aperture is 51 times that of your eye, collecting 510,000 photons a second all of which, thanks to the 7x magnification, are getting into your eye; now you can see it\*. If this galaxy is so tiny that it’s filling illuminating only a fraction of _one_ rod receptor in your eye, then yes, a telescope will collect more photons and shove it into one receptor in your eye. But most galaxies are not that small. Each rod cell subtends about 1/2 arcminute. M104, for example (which I think is one of the smaller galaxies on the Messier catalog), is about 9 x 4 arcmin. So **Chronos** is correct. The telescope _is_ just magnifying the view, not making it brighter. A 7x50 telescope may collect 51 times more light than your naked eye, but that light is spread over a larger area (51 times larger) of your retina. So each rod cell isn’t receiving any more light than without the telescope. The reason M104 is visible through a telescope but not with naked eyes is because the human brain has some ability to average the signals from multiple receptors. If 10 adjacent rod cells receive 100 photons / second each, that might be dismissed by your brain as noise. But with 7x50 binoculars, you now have 510 adjacent rod cells each receiving 100 photons/second, and now _that_ is seen as a feature. (The actual numbers may not be accurate, they are to illustrate the math.) > [@](#): > > That’s right, it won’t because there’s plenty enough light that when you peer though the eyepiece, your iris contracts even further than it does when you’re gazing directly. I haven’t tried it, but I’d bet an exposure meter held up to the eyepiece would read higher than one aimed at the wall. No, it has nothing to do with your iris contracting. Try it. Put an exposure meter behind the lens, or point a camera into the eyepiece. You will **never** register a higher surface brightness. Or for that matter, just try holding up a magnifying glass up against the blue sky (_nowhere near the sun_) and see if the blue sky looks any brighter through the magnifying glass. It won’t. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [July 17, 2017, 6:01pm UTC](https://boards.straightdope.com/t/could-the-visible-light-images-of-some-galaxies-look-the-same-to-us-as-the-hubble/791256/25 "2017-07-17T18:01:59Z")
p.s. A more formal way to say “a telescope cannot increase apparent surface brightness” is to say [etendue is conserved](https://en.wikipedia.org/wiki/Etendue#Conservation_of_etendue). An optical system can increase etendue but it can never decrease it. ---
**Author:** ![DesertDog](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/desertdog/32/11503_2.png) [@DesertDog](https://boards.straightdope.com/u/DesertDog)\ **Post date:** [July 17, 2017, 7:35pm UTC](https://boards.straightdope.com/t/could-the-visible-light-images-of-some-galaxies-look-the-same-to-us-as-the-hubble/791256/26 "2017-07-17T19:35:55Z")
Well, I spent an hour creating the reply to your and **Chronos** ’ opinions, complete with [del]appeals to authority[/del] citations. I know what I have seen. Perhaps is it some sort optical illusion, bigger apertures allowing you to see objects too dim to be seen unaided. If so, it’s been a pervasive illusion, persisting since 1608 and leading deluded astronomers to make [bigger](https://en.wikipedia.org/wiki/Lick_Observatory) and [bigger](https://en.wikipedia.org/wiki/Palomar_Observatory) telescopes, poor sods. I am done here; I have other things to do. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [July 17, 2017, 8:01pm UTC](https://boards.straightdope.com/t/could-the-visible-light-images-of-some-galaxies-look-the-same-to-us-as-the-hubble/791256/27 "2017-07-17T20:01:25Z")
> [@DesertDog](#): > > Well, I spent an hour creating the reply to your and **Chronos** ’ opinions, complete with [del]appeals to authority[/del] citations. I know what I have seen. Perhaps is it some sort optical illusion, bigger apertures allowing you to see objects too dim to be seen unaided. If so, it’s been a pervasive illusion, persisting since 1608 and leading deluded astronomers to make [bigger](https://en.wikipedia.org/wiki/Lick_Observatory) and [bigger](https://en.wikipedia.org/wiki/Palomar_Observatory) telescopes, poor sods. > > I am done here; I have other things to do. Nothing **Chronos** and I wrote imply that large telescopes are useless. Of course they serve a function. Even for visual use, a large telescope allows you to see dimmer point sources (stars), and enlarges the view of extended objects, allowing you to see dimmer objects (because your eye/brain has a lot more illuminated rods to work with). Which is why I own a pair of [100mm ED-Apo binoculars](http://www.apm-telescopes.de/en/binoculars/giant-binoculars-100mm-aperture-more/apm-100-mm-90-ed-apo-binocular-125-eyepiece-sockets) and a 14-inch Dobsonian. And for non-visual (i.e. film, CCD and other sensors), aperture is even more important because film & sensors are not limited by a pupil - you can make them as large as you want, and collect more light. My colleagues and I once did a concept study for an 8-meter _solar_ space telescope for this reason. But no matter how you look at it, it’s impossible for an optical instrument to _increase the apparent surface brightness_ of an extended object. You can calculate the flux based on geometric optics, or you can argue from the standpoint of etendue, or consider the laws of thermodynamics (i.e. if a telescope could amplify the apparent surface brightness, it would be possible to make a telescope whose focal plane receives more light than the original object, i.e. heat flows from a cooler surface to a hotter surface.) ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [July 17, 2017, 9:42pm UTC](https://boards.straightdope.com/t/could-the-visible-light-images-of-some-galaxies-look-the-same-to-us-as-the-hubble/791256/28 "2017-07-17T21:42:51Z")
> [@](#): > > Quoth **DesertDog** : > > For all intents and purposes, stars are point sources of light. Any enlargement you see of a magnified star is due to the limitations of the optics, not the star’s disk getting larger. A star _is_ a disk, whether you can resolve it or not. A telescope aimed at a star will turn a disk that’s too small to see into a disk that’s larger but still too small to see. You won’t see evidence of the magnification from an increase in size of the disk, but you will see evidence of the magnification from the increase in brightness. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [July 17, 2017, 10:23pm UTC](https://boards.straightdope.com/t/could-the-visible-light-images-of-some-galaxies-look-the-same-to-us-as-the-hubble/791256/29 "2017-07-17T22:23:05Z")
[Here](http://www.deepskywatch.com/telescope-calculator.html) is a telescope & eyepiece calculator spreadsheet, which produces a graph of apparent magnitude as seen through a telescope. Note as magnification is increased, the blue line (apparent magnitude of an extended object) stays flat until the exit pupil matches the eye’s pupil. After that the apparent magnitude increases (gets darker). Point sources don’t get darker because the apparent size of a point source stays the same. (At least it’s approximated as such. In reality it increases slightly due to atmospheric distortion and diffraction.) The page also explains: > [@](#): > > One of the purposes of this calculator is to bring attention to a topic often unfamiliar to amateur astronomers: The fact that apparent surface brightness (intensity per area of our retina as we see it) of extended deep sky object never actually increases, no matter which telescope or eyepiece we shall use. > > Assume we observe Andromeda galaxy with our naked eyes. There is a certain amount of light denisty (per square metre) falling on our eye’s retina - irradiance if we use radiometric therminology, or we may simply call it apparent surface brightness. If we take a telescope and use magnification which gives us brightest possible image (exit pupil equals to dark adapted eye’s pupil which is approximately 6-7mm) There will be no change in apparent surface brightness of the object, meaning Irradiance on our retina will stay the same. A mathematical proof to this is included in attached Excel file, though it can simply be backed by “Radiance Conservation Law” or “Extent Conservation Law” which is ultimately a conservation of energy. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [July 17, 2017, 10:27pm UTC](https://boards.straightdope.com/t/could-the-visible-light-images-of-some-galaxies-look-the-same-to-us-as-the-hubble/791256/30 "2017-07-17T22:27:50Z")
p.s. I can appreciate this is counter-intuitive to amateur astronomers who have always been taught that aperture is everything, and experienced first-hand how telescopes and binoculars allow us to see deep-sky objects that are invisible to the naked eye. But it’s all an illusion, mainly stemming from the fact that the human eye does a very good job of filtering noise and integrating signal. A large dim object _appears_ brighter than a smaller and equally dim (same surface brightness) object. [Here’s a good discussion on the Cloudy Nights amateur astronomy forum](https://www.cloudynights.com/topic/28970-aperture-vs-surface-brightness/) on this very topic. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [July 17, 2017, 10:29pm UTC](https://boards.straightdope.com/t/could-the-visible-light-images-of-some-galaxies-look-the-same-to-us-as-the-hubble/791256/31 "2017-07-17T22:29:35Z")
p.p.s. [Here’s another very good explanation](http://www.rocketmime.com/astronomy/Telescope/SurfaceBrightness.html). > [@](#): > > What the heck is that saying? What – that the very brightest image I can get with the scope is exactly the same brightness that I see with the naked eye??? > > Yup. > > Well, remember we’re talking about surface brightness, meaning the brightness per unit area, or the brightness density. At the minimum magnification, which is the brightest image you can get, the surface brightness is exactly the same as what you see with your eye. Of course, the image is 30, 40, 50, even 60+ times bigger at that brightness, so it might be as much as 4000 times the total brightness, depending on the diameter of the objective. But the surface brightness never exceeds what you can see with your eye alone. ---
**Author:** ![D18](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@D18](https://boards.straightdope.com/u/D18)\ **Post date:** [July 19, 2017, 7:37pm UTC](https://boards.straightdope.com/t/could-the-visible-light-images-of-some-galaxies-look-the-same-to-us-as-the-hubble/791256/32 "2017-07-19T19:37:25Z")
Back to the OP, fellas! Sorry to be late to the party. How closely does [this image](https://www.nasa.gov/sites/default/files/thumbnails/image/iss041e045469.jpg) replicate a naked-eye view of the Milky Way from space? From Earth, I believe you would only get those colours and intensity with a long exposure/stacked images. The source doesn’t say anything about the exposure/manipulation of the image (although it would be hard to do a long exposure, with that clarity, moving 7 kps, no?) ---
**Author:** ![AHunter3](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ahunter3/32/368_2.png) [@AHunter3](https://boards.straightdope.com/u/AHunter3)\ **Post date:** [July 19, 2017, 9:18pm UTC](https://boards.straightdope.com/t/could-the-visible-light-images-of-some-galaxies-look-the-same-to-us-as-the-hubble/791256/33 "2017-07-19T21:18:07Z")
A lot of people’s answers assume we’ve got our little feets planted on the earth. If we garbed ourselves in an appropriate space-suit and positioned ourselves in the darkness between galaxies and stared at, for instance, [the one mentioned by the OP](http://spacetelescope.org/images/heic0506a/), with no bright stars anywhere nearby to mess up our night vision and no atmosphere to obscure stuff, what would our human eyeballs be able to see? ---
**Author:** ![Lemur866](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lemur866/32/434_2.png) [@Lemur866](https://boards.straightdope.com/u/Lemur866)\ **Post date:** [July 19, 2017, 10:42pm UTC](https://boards.straightdope.com/t/could-the-visible-light-images-of-some-galaxies-look-the-same-to-us-as-the-hubble/791256/34 "2017-07-19T22:42:46Z")
Well, one thing to remember is that the human eye is many times more sensitive than a typical camera. I’m sure you’ve had the experience of looking at clouds or sunsets or distant mountains, you try to photograph it and in the picture the features are completely washed out and have none of the detail you saw with your naked eye. Or you’re in dim light and take a picture of an object you can see easily and the photo is pretty much just black. So…apparent brightness is a tricky thing. An object can be very very dim, and if there’s no other light source you can see it clearly, even though if you tried to take a picture you’d see nothing. So if you’re hovering in intergalactic space looking at a nearby galaxy with no other light sources, you’ll see something like that spiral galaxy in your picture. But that galaxy will actually be much dimmer than the picture. You’re in a bright room right now and you can easily see the galaxy in the picture on your monitor, right? But if you were in a bright room and tried to look at the real galaxy you wouldn’t be able to see it because it would be many times dimmer than that image on your monitor. ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [July 19, 2017, 11:24pm UTC](https://boards.straightdope.com/t/could-the-visible-light-images-of-some-galaxies-look-the-same-to-us-as-the-hubble/791256/35 "2017-07-19T23:24:55Z")
> [@D18](#): > > Back to the OP, fellas! Sorry to be late to the party. > > How closely does [this image](https://www.nasa.gov/sites/default/files/thumbnails/image/iss041e045469.jpg) replicate a naked-eye view of the Milky Way from space? From Earth, I believe you would only get those colours and intensity with a long exposure/stacked images. The source doesn’t say anything about the exposure/manipulation of the image (although it would be hard to do a long exposure, with that clarity, moving 7 kps, no?) > [@AHunter3](#): > > A lot of people’s answers assume we’ve got our little feets planted on the earth. > > If we garbed ourselves in an appropriate space-suit and positioned ourselves in the darkness between galaxies and stared at, for instance, [the one mentioned by the OP](http://spacetelescope.org/images/heic0506a/), with no bright stars anywhere nearby to mess up our night vision and no atmosphere to obscure stuff, what would our human eyeballs be able to see? OP here \* pauses from munching popcorn \* Yup, that’s the OP all right. I think way up someone mentioned the posish: sitting on my armchair armed only with a beer perched somewhere in intergalactic space, what or where could I get the best postcard-pretty view. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [July 20, 2017, 2:17am UTC](https://boards.straightdope.com/t/could-the-visible-light-images-of-some-galaxies-look-the-same-to-us-as-the-hubble/791256/36 "2017-07-20T02:17:38Z")
> [@AHunter3](#): > > A lot of people’s answers assume we’ve got our little feets planted on the earth. > > If we garbed ourselves in an appropriate space-suit and positioned ourselves in the darkness between galaxies and stared at, for instance, [the one mentioned by the OP](http://spacetelescope.org/images/heic0506a/), with no bright stars anywhere nearby to mess up our night vision and no atmosphere to obscure stuff, what would our human eyeballs be able to see? The atmosphere hardly makes any difference. It absorbs very little visible light - only a couple of percent at most. [See here](http://what-when-how.com/remote-sensing-from-air-and-space/atmospheric-absorption-scattering-and-turbulence-visible-imagery-remote-sensing/) for example - keep in mind that the human eye is only sensitive from 400nm to 700nm or so. That’s just the first 3 tick marks in the plot. The image you linked to looks impressive because it’s a long-exposure photo. You can get very similar photos from the ground under a dark sky with a similarly long exposure time. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [July 20, 2017, 2:30am UTC](https://boards.straightdope.com/t/could-the-visible-light-images-of-some-galaxies-look-the-same-to-us-as-the-hubble/791256/37 "2017-07-20T02:30:38Z")
> [@Lemur866](#): > > Well, one thing to remember is that the human eye is many times more sensitive than a typical camera. I’m sure you’ve had the experience of looking at clouds or sunsets or distant mountains, you try to photograph it and in the picture the features are completely washed out and have none of the detail you saw with your naked eye. Or you’re in dim light and take a picture of an object you can see easily and the photo is pretty much just black. Actually, modern digital camera sensors are far more efficient than the human eye. By some estimates the human eye is only 1-2% efficient ([cite](http://www.sciencedirect.com/science/article/pii/0042698978901608). Even a basic CCD in a digital camera has \>10% efficiency, and modern back-illuminated sensor may have \>80% efficiency. The human eye does have a huge _dynamic range_, so you can look at bright & dark features at the same time. Digital cameras can only match this by taking multiple images at different exposure times and then combining those images ([HDR imaging](https://en.wikipedia.org/wiki/High-dynamic-range_imaging)). Most high-end cameras and phones have this feature now. If your camera isn’t as good at imaging in dim light, it’s because your eyes have very good image stabilization, and your brain is very good at ignoring noise and detecting patterns in what you see. > [@](#): > > So if you’re hovering in intergalactic space looking at a nearby galaxy with no other light sources, you’ll see something like that spiral galaxy in your picture. No it won’t. There is a hard limit on how far your pupils can open up, no matter how dark it is. It’s around 7mm. You can reach it on earth in a dark site, far away from city lights, on a moonless night. Going into intergalactic space won’t make your eyes any more sensitive than that. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [July 20, 2017, 2:35am UTC](https://boards.straightdope.com/t/could-the-visible-light-images-of-some-galaxies-look-the-same-to-us-as-the-hubble/791256/38 "2017-07-20T02:35:24Z")
> [@Leo\_Bloom](#): > > OP here \* pauses from munching popcorn \* > > Yup, that’s the OP all right. I think way up someone mentioned the posish: sitting on my armchair armed only with a beer perched somewhere in intergalactic space, what or where could I get the best postcard-pretty view. The answer is, it won’t look any more impressive than our own galaxy (the Milky Way) does to your eyes, from a dark sky site (no light pollution, no moonlight). Which I think _is_ pretty impressive, but you won’t see vivid colors like those Hubble photos. Because the cones (the color-sensitive light receptors in our eyes) only respond to bright light. In dim light, our eyes only work in monochrome. ---
**Author:** ![D18](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@D18](https://boards.straightdope.com/u/D18)\ **Post date:** [July 20, 2017, 11:43am UTC](https://boards.straightdope.com/t/could-the-visible-light-images-of-some-galaxies-look-the-same-to-us-as-the-hubble/791256/39 "2017-07-20T11:43:13Z")
> [@scr4](#): > > The answer is, it won’t look any more impressive than our own galaxy (the Milky Way) does to your eyes, from a dark sky site (no light pollution, no moonlight). **Which I think _is_ pretty impressive** , but you won’t see vivid colors like those Hubble photos. Because the cones (the color-sensitive light receptors in our eyes) only respond to bright light. In dim light, our eyes only work in monochrome. Bolding for emphasis. You’ve got that right! I’m heading to our cottage next week, and one of my favourite things about it is it is dark enough to see the Milky Way. I can’t wait! ---
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [July 20, 2017, 12:47pm UTC](https://boards.straightdope.com/t/could-the-visible-light-images-of-some-galaxies-look-the-same-to-us-as-the-hubble/791256/40 "2017-07-20T12:47:41Z")
> [@D18](#): > > How closely does [this image](https://www.nasa.gov/sites/default/files/thumbnails/image/iss041e045469.jpg) replicate a naked-eye view of the Milky Way from space? From Earth, I believe you would only get those colours and intensity with a long exposure/stacked images. The source doesn’t say anything about the exposure/manipulation of the image (although it would be hard to do a long exposure, with that clarity, moving 7 kps, no?) One rule of thumb is to count the stars! There’s something like 2-4 thousand stars visible to the naked eye from the Earth’s surface. That’s about half the sky. Your photo shows quite a bit more than that in a smaller segment. So not completely accurate but maybe off one order of magnitude. (I did a sample count on one small square but the motion blur really hurts the count. A more stable image would should quite a few more.) [Previous page](https://boards.straightdope.com/t/could-the-visible-light-images-of-some-galaxies-look-the-same-to-us-as-the-hubble/791256.md?page=1) [Next page](https://boards.straightdope.com/t/could-the-visible-light-images-of-some-galaxies-look-the-same-to-us-as-the-hubble/791256.md?page=3)