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Star views from the ISS

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#1 REC

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Posted 09 February 2013 - 10:17 AM

Every once in a while I check into NASA to see what they are broadcasting. Today one of the astronauts was taking questions from schools and one person from an astronomical soceity in the UK asked what the stars look like from space. The guy taking pictures of Earth was explaining that most of his viewing is of the planet and he is surrounded by a lot of light from the ISS. But, he said there is a window facing up that is away from all the light and he can see space pretty well, especially when they are in the Earths shadow.

He said the sky is very bright with all the stars visible and constellations completely disappear because of all the stars that are shining. Also, he said dark nebula was very prominent and well defined. Almost like there was a blanket thrown over parts of the sky.

I always wanted to ask that question and it was fascinating to hear him describe it. I wonder what the visible magnitude is up there? You talk about the ultimate dark sky observing sight!!!

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#2 MG1962

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Posted 09 February 2013 - 11:37 AM

I want to say I've read that it 8 or 8.5. The thing is it is the seeing thats dramatically improved. Which means contrast and such is off the charts as well.

#3 Mike B

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Posted 09 February 2013 - 12:12 PM

That sounds right. I'd assume that from high-mountain observatories (ie. 10-15k feet elev.), and away from populations (ie. LP sources), you'd be 90% of the way to spaced-out views. Still, to hear the actual numbers on that, say by 10k foot elev. intervals headed toward "space", would be most fascinating! :jump:

#4 GlennLeDrew

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Posted 09 February 2013 - 01:21 PM

Even at the top of a tall mountain, one is nowhere near to being "90% of the way to spaced out views." For one thing, there is still about 1/2 the atmosphere remaining, albeit a lot drier and (usually) cleaner. But more importantly, there is still remaining the air glow layer at an altitude of 80 km or so. (Google "airglow from earth orbit" to see a neat picture of it hovering as a greenish 'force field'-like glow above the surface.) Some sources put this at the top of the list of sky brighteners from pristine sites where artificial light pollution is not a factor.

I've read in a graduate-level book published by Princeton University Press that from space proper, and above the airglow layer *and* aurorae (which extend very much higher), the sky is some 1.5 magnitudes, or a factor of 4 darker than from the best sites on earth.

From earth orbit there is still zodiacal light to contend with, the brightness of which is strongest along the ecliptic plane, particularly toward the Sun. The darkest regions would be toward the ecliptic poles, but displaced somewhat in the anti-solar direction.

A sky 1.5 magnitudes darker than we earthbound observers could ever experience would be a marvelous sight indeed! After all, near the limit of sky darkness on earth, a seemingly tiny difference of 0.2 magnitudes makes for a most definite difference. The contrast boost on the milky way would be phenomenal, with the dark clouds truly jumping forth into prominence.

I'd hesitate to say that the gain in stellar limiting magnitude would necessarily be of the same 1.5 magnitudes, however. Just because the 'background' has gotten darker by some amount does not automatically imply that a faint threshold point source fainter by the same amount will become visible, for in this regime of image brightness the eye's response is poorer due to visual system noise.

To illustrate. With a telescope we can darken the sky by going to higher power, which makes the exit pupil smaller. Indeed, we do note that this brings into view fainter stars. But the faintness limit does not track with the amount of sky darkening. Compared to the sky brightness as seen when the exit pupil is as large as the observer's own pupil, at the smaller exit pupils where the faintest stars are revealed the sky will have been darkened by a good 4 magnitudes. But we most certainly do not see stars fainter by this amount; about 1.5 magnitudes fainter would be more typical.

Hopefully for our astronauts the porthole through which they peer is clean and has good transparency, and that ambient light and reflections during the brief 45 minute night can be well suppressed. If not reasonably well dark adapted, the gains afforded by their unique perch cannot be fully appreciated.

#5 Mike B

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Posted 09 February 2013 - 03:23 PM

...there is still about 1/2 the atmosphere remaining, albeit a lot drier and (usually) cleaner.


Yes, i was assuming that, as well as the half the atmo aspect. Didn't realize about the "glow" issue, tho... i have zip experience with high-altitude environments, and enjoy only occasional visits to "blue" dark-skies. Never been to a "gray" zone, or darker.

I found this article quite fascinating! With ample acclimatization, apparently human vision can adapt to ~14,000 elevation! Yet even stranger were the results they obtained (page 3 @ the linked article)... the added elevation beyond 6,800' seemed of little benefit for LM.

So perhaps clean, dry air & the lack of nearby LP is the majority of what one can hope for- save for getting into orbit? The "thinning" of atmo with elevation would seem to be a distant second in terms of limiting magnitude? Altho i'm sure that's not a linear relationship, and results between sea-level & 7,000' might be somewhat more significant than those going from 7k to 14k'.

Also in the equation would be, i'd assume (again), less atmo scintillation- so possibly better resolution of faint point-sources as one gained altitude. The ultimate here would be what's seen from orbit- zero scintillation!

If the 1.5 magnitude gain over atmoshperic LM seen from low-orbit is true, then the 8.5 LM estimate noted previously would sound about right, then.

A truly fascinating subject!

#6 careysub

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Posted 09 February 2013 - 03:39 PM

It would be nifty to beat the resolution of any Earth-bound instrument of the pre-adaptive optics era with your 18" reflector.

#7 Tony Flanders

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Posted 09 February 2013 - 07:08 PM

I found this article quite fascinating! With ample acclimatization, apparently human vision can adapt to ~14,000 elevation! Yet even stranger were the results they obtained (page 3 @ the linked article)... the added elevation beyond 6,800' seemed of little benefit for LM.


Very interesting. And (unusually) it confirms common sense. It makes sense that people can adapt fully to 14K feet -- after all, there are substantial populations living considerably higher than that. And it makes even more sense that there's no significant difference between 6800 and 13600 feet -- why should there be? The added extinction due to air molecules alone is tiny. As I said before, the whole point of going high is to get above air pollution, both natural and artificial. Of which there's precious little in Hawaii.

#8 mogur

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Posted 10 February 2013 - 12:02 AM

Am I right in assuming that, from the blackness of space, the so called "dark nebulae" would actually be brighter than the surrounding sky?

#9 GlennLeDrew

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Posted 10 February 2013 - 12:59 AM

Even from Earth, some dark nebulae have parts which are brighter than the darkness between stars in adjacent 'unobscured' regions. This illumination for the most part comes from integrated light of the milky way galaxy, and in some cases is augmented by nearby stellar associations. But in most cases, in order to see this it takes image processing to effectively subtract the sky glow.

But with a reduction in sky brightness of some 1.5 magnitudes, the dark nebula portions illuminated by the Milky Way will be more readily discerned in images. I doubt that except for a few scant possibilities, the surface brightness/contrast of these lit up clouds would still be too low for visibility by eye. Note that I'm not including here the 'classical' reflection nebulae, which are illuminated by either embedded or proximate stars.

#10 BrooksObs

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Posted 10 February 2013 - 09:15 AM

I would contend that an astronaut's view of the sky from the ISS would have nowhere near a LM of magnitude 8.5 by virtue of a number of factors.

Firstly, it is highly unlikely that anything like full dark adaptation would be reached by an individual during the interval that ISS was fully within the earth's shadow, after having been in bright daylight an equal interval. Likewise, I'm sure that the interior of the ISS is not without some form of illumination at all times.

Secondly, astronauts are certainly not amateur astronomers and are unlikely to have intimate familiarity with the appearance of a truly dark sky, at best having occasionally viewed planetarium simulations of such. Thus, when presented with such a real sky they would likely feel overwhelmed by the scene.

Consider further that the observer does not detected the very faintest stars likely visible at a give site with just a casual look. It is necessary to spend quite a bit of time examining the sky to detect stars truly near one's limit. Given that an astronaut is not on the ISS for a joyride, it would be highly unlikely that he can allot the necessary time to do so.

In addition, those who have flown at night cross country and looked out the cabin windows will know that the limited angle of view seems to dramatically enhance a star-congested impression of the sky, clearly an illusion of some sort, creating a scene that seems far beyond what is ever seen from the ground. However, a careful check shows a LM no greater than seend from the ground (I've done this many times).

Therefore, I would say that regardless of the gain "theoretically" possible by being totally outside the atmosphere, I highly doubt that any astronaut has viewed the heavens appearing any more impressive than an earthbound observer sees from a Bortle class 1 site.

BrooksObs

#11 REC

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Posted 10 February 2013 - 11:03 AM

Interesting perspective and I can see how some of these conditions would effect the views from the ISS. I have seen some of the views they have from that Coupala thing they have, looks like a picture window of some kind.

#12 CharlesW

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Posted 10 February 2013 - 02:25 PM

While it is probably true that the astronauts don't have much free time to look out that porthole, they could certainly employ some of the same adaptation methods that we have available, such as red goggles or an eye patch.

#13 Mike B

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Posted 10 February 2013 - 04:55 PM

He said the sky is very bright with all the stars visible and constellations completely disappear because of all the stars that are shining.


...astronauts are certainly not amateur astronomers and are unlikely to have intimate familiarity with the appearance of a truly dark sky, at best having occasionally viewed planetarium simulations of such. Thus, when presented with such a real sky they would likely feel overwhelmed by the scene.



I dunno... *i* am an amateur astronomer, and when i get to my group's "blue" observing site, i too am generally overwhelmed at the scene. It takes a bit to get re-acclimated, able to spot the familiar patterns amongst the crowded sky! Actually, i suspect i rather enjoy that! :jump:

Whether the average astronaut is an "amateur astronomer" or not i have no idea. But i have a hard time imagining anyone willing to go thru the nit-picky selection process, then the grueling training, and entertain the rather substantial risks, would go to such lengths (heights :question:) without having significant interests in "what's up there".

And wouldn't part of that preparation involve some "lights out" training?... as well as basic Astronomy for orientation purposes (should the computer and/or power go on a temporary "excursion")?

Therefore, I would say that regardless of the gain "theoretically" possible by being totally outside the atmosphere, I highly doubt that any astronaut has viewed the heavens appearing any more impressive than an earthbound observer sees from a Bortle class 1 site.

While that may or may not be the case for many ISS occupants, i'm quite sure it is NOT the case for "astronauts" in general. As a class, they have done more than a few EVA's, Lunar orbits, and walks. Perhaps a fun search would be to find some of their personal references & descriptions as to what they've seen in this regard!

What the OP has quoted is enough to give me goosebumps:

...he said there is a window facing up that is away from all the light and he can see space pretty well, especially when they are in the Earths shadow... dark nebula was very prominent and well defined. Almost like there was a blanket thrown over parts of the sky.

And that without adequate dark-adaptation.
:waytogo:

#14 bunyon

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Posted 11 February 2013 - 08:59 AM

Why the assumption that astronauts are NOT amateurs? Granted they all aren't. And the ones that are have rather busy jobs. But I'm pretty sure I've read of several who were - that without an exhaustive search. I'd guess the number of astronauts who know their constellations would be pretty high.

#15 BrooksObs

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Posted 11 February 2013 - 09:54 AM

I have no doubt that nearly all of the astronauts "know the constellations", parts of their jobs depend upon that, but I have never heard of even one actually claiming to have ever been a practicing amateur astronomer, nor being intimately familiar with observational astronomy. There is an enormous difference between perhaps having a casual interest in amateur astronomy (as many claim to have) and actual having a serious working knowledge. Even among the amateur community represented here there are those of us that are more rightly classified as simply star gazers rather than serious amateur astronomers well versed in observing methodology.

BrooksObs

#16 bunyon

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Posted 11 February 2013 - 11:33 AM

You may well be right. But I would swear to having read of several who, while not going to the obsessive and compulsive ends of the hobby many of us enjoy, would be considered amateur astronomers. But it's distant memory (and another generation of astronauts, come to think of it).

But, look, I volunteer to go up and have a look through that porthole to test this. You can even come along to increase the observational set. ;)

#17 Kevdog

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Posted 13 February 2013 - 04:59 PM

I have no doubt that nearly all of the astronauts "know the constellations", parts of their jobs depend upon that, but I have never heard of even one actually claiming to have ever been a practicing amateur astronomer, nor being intimately familiar with observational astronomy. There is an enormous difference between perhaps having a casual interest in amateur astronomy (as many claim to have) and actual having a serious working knowledge. Even among the amateur community represented here there are those of us that are more rightly classified as simply star gazers rather than serious amateur astronomers well versed in observing methodology.

BrooksObs


Funny, we watch NasaTV quite a lot. Many (or at least several) of the astronauts are also astrophotographers and take their equipment up to get photo ops (of the stars, not just the earth) even with the very very limited time they get.

Oh yes, and the first link given for a google of "astrophotography from the ISS" is nasa's own site with links to tons of pictures!
http://science.nasa....mar_noseprints/

"There's always something good to see out the window of the space station," says Pettit, who happens to be an amateur astronomer as well as the science officer of the International Space Station (ISS).


Posted Image

"These pictures show how wonderfully stable the space station is," says Pettit. "When the camera is mounted to the window, the ISS itself serves as a tripod. Any movement would cause streaks in the star images." But the station's Control Moment Gyros maintain attitude with rock-solid precision. "I don't believe that the ISS was designed for astronomy," adds Pettit, "but it functions very well as a platform for astrophotography."



#18 REC

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Posted 13 February 2013 - 05:33 PM

Wow, this is great!

Thanks for posting:)

Bob

#19 MikeMcCaskey

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Posted 14 February 2013 - 12:32 PM

Ditto - :thanx: :thanx: :thanx:

Not to hijack the thread......but are there any similar reports from the men who walked on the moon???

#20 GlennLeDrew

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Posted 14 February 2013 - 02:50 PM

The sunlit lunar surface, and any sunlight spilling into the upward facing docking window, would make it hard for the Apollo astronauts to dark adapt. The CM pilot could enjoy darkness when over the night side...

#21 MikeMcCaskey

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Posted 14 February 2013 - 03:00 PM

Glenn. Wondered if the surface reflection would wash out much of the sky. Had not thought about the CM pilot. Be cool to ask the ones still alive!!!! Mike

#22 Starman81

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Posted 15 February 2013 - 11:31 AM

Ditto - :thanx: :thanx: :thanx:

Not to hijack the thread......but are there any similar reports from the men who walked on the moon???


Same here, but have to ask... How about night sky views from Mars?? The Rovers are there but I don't think I have seen a single night sky image from Mars. Perhaps the cameras onboard were not made for taking astro photos? :question:






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