Re: Stars Are Thousands Of Times Closer Than They Appear
We can get a rough estimate of the distance by just asking how far away would the Milky Way have to be to have that apparent size and brightness?
I'm sorry to bust into this discussion. And i'm no scientists and don't even know how to exactly calculate parallax. (i understand the basic of it) But how do "We" even know our own galaxy (milky way) apparent brightness if not seen from so many light years ? or the apparent size ?
I've seen artist impressions with an arrow "we are here" but if the arms are to opaque or to dense to really look trough how do we know how it looks like ?
( i might be asking silly questions and if so then please ignore my post and continue on with the discussion, no hard feelings )
Nitai
Re: Stars Are Thousands Of Times Closer Than They Appear
Lloyd wrote:
Gary said: The way the planets shine, IMO, is not from the reflection of visible light from the Sun, but by the generation of UV and X-rays from ionisation of the elements surrounding the planets. It is only our atmosphere, or portions of it, that allow us to see the stars, and that is why they must use instruments and not just ordinary telescopes to view the stars from off-world.
* I'm pretty sure your theory is wrong. The moon is rather gray and white both to the naked eye from Earth and from spacecraft photos. Mars is reddish both to the naked eye on Earth and from spacecraft photos. The Sun also seems to look the same color, whether from Earth or near-Earth satellites. * Satellites orbiting Earth take pictures of Earth, which we can see on internet as satellite maps, like Google, Yahoo etc. The satellites are about 100 miles high, above most of the atmosphere, so planetary light obviously gets through the atmosphere. We have pictures of Earth from the Moon etc. * When light goes through an atmosphere, the frequency doesn't change. All that happens is that some of the light is absorbed. Most x-rays and gamma rays are absorbed. We can see forests from many miles away that look green. Light goes through water and glass without changing frequencies, though some of the light is absorbed. In the oceans light only penetrates some tens of meters, but blue penetrates the deepest.
Why can't we see stars in this picture? Just wondering..
Re: Stars Are Thousands Of Times Closer Than They Appear
hi Lloyd,
Lloyd wrote:
nick c wrote: Sirius is many thousands of times brighter than Pluto. It cannot be a small object far away, what kind of small object could emit that bright of a light?
* Did you misspeak there? We're suggesting that Sirius may be a smaller object that's closer than assumed, not farther.
Yes, I should have written a small object "close by" instead of "far away." GaryN has written here that most stars that are considered in the local galactic neighborhood are actually planets revolving around the Sun...is this your position? That would include Sirius, no? (Note: if you are not taking the same position as GaryN then you probably can disregard the rest of this paragraph) I am saying that Pluto is a small object at a distance from the Sun, yet it shows a disk even though its' magnitude is +13 or more. Yet Sirius is thousands of times brighter and shows no disk. So, what type of small object could emit that bright of a light? if it is not a star? You use the number of 1000 AU, but Pluto is only 39 AU. What would Jupiter look like at that (1000 AU) distance, would it even be visible to the naked eye? So what type of object is Sirius, where is it located, how is it's light being emitted if it is not a star? Is it reflecting light, if so from where? Is it emitting it's own light, if so how? If it is emitting its' own light than why would you not call it a star? There are just a lot of things with this hypothesis that just do not make sense to me.
Does the parallax method involve observing an object and its background at 6 month intervals when the angle from the object to the 2 different positions of Earth is at a maximum angle?
Yes, a triangle with a base of 186 million miles.
How would an astronomer know that the background stars haven't moved significantly in that 6 month interval?
The sky appears as a sphere overhead. It is mapped in a celestial coordinate system somewhat similar to the lines of latitude and longitude on a globe, except that the coordinates are declination and right ascension. Star positions are plotted within these coordinates. If a star has moved then its' RA and/or Dec will have changed. If a star maintains its' celestial coordinates even 6 months later, then it must be at a distance beyond the range of the geometrically calculated parallax technique, which to my understanding is somewhere in the neighborhood of 500 ly, give or take. I am not sure if Hipparcos extends this much further. Of course this is oversimplified, everything is moving, but the method seems to me to be reasonable.
Lloyd wrote:
nick c wrote: I do not think there is any reason to doubt that we are in a spiral galaxy of immense size, accompanied by several small satellite galaxies and dozens of globular clusters all of which are resolvable into stars. And we can see other nearby spiral galaxies with their attending satellite galaxies and globular clusters, and can resolve them into stars. We can get a rough estimate of the distance by just asking how far away would the Milky Way have to be to have that apparent size and brightness?
* Your statement of faith doesn't seem to help much to explain how we can be certain that stars and galaxies etc are as distant as is normally assumed. I hope to hear soon of a reliable means to determine distances, whether by parallax or anything else.
No, not in anyway a "statement of faith." Like anyone, I am looking at the evidence presented and the assumptions involved and making an evaluation. Since information is incomplete I have to make assumptions, and choose the model which best fits. However this minaturized version of the visible universe imhop, does not offer a viable alternative interpretation. It is a throwback to a bygone era, and has been superseded by a better scheme which better fits the observations. If a galaxy is conventionally measured at 10 million ly away, but actually is half the size and only 5 million ly away...well, it is still very far away. Even though many of the conventional measuring yardsticks are called into question, we are still dealing with immense distances.
To me, it is not an unrealistic assumption that the "stars" are objects like our Sun only far removed. This is why most of them maintain their celestial coordinates for long periods of time and why we can only detect them by their light, ie, they are not resolvable as disks. We can see globular clusters such as M13 or satellite galaxies like the Magellanic Clouds and resolve them into component stars, furthermore, we can see globular clusters just like M13 and satellite galaxies like the Magellanic Clouds, accompanying other galaxies. Some of the larger, brighter, and hence nearer galaxies are resolvable into stars. The Milky Way looks like a cloud in a clear night sky and telescopically it resolves into millions of stars. The appearance of the Milky Way is what would be expected from the view of a planet located in one of the arms of a spiral galaxy. I have seen no evidence that refutes that stars are what we thought they are...distant Suns. In fact some of those stars have spectrums that are similar and even identical to our Sun. And that galaxies are typically composed of untold numbers of these suns. Well, for now I would prefer to end my participation in this thread, barring any unforseen questions. I am going to reread Revolution In Astronomy when I get a chance, so maybe I'll be back with some more comments or questions.
Nick
GaryN
Re: Stars Are Thousands Of Times Closer Than They Appear
Hi Nitai,
Why can't we see stars in this picture? Just wondering..
I'd say because the exposure time is too short, due to the brightness of the snow, ice, clouds. As an aside, I was wondering about the human eye, and just how sensitive it is. The other night, there were some stars showing, not many and not very bright as I live in an area with a lot of misty marine air. I went from a normally lit room to outside, and the stars were visible. I looked at my 100W porch light for a few seconds, looked back to the sky, and could still see the stars. Then I tried looking up, closing my eyes for a few seconds, and then opening them very briefly, blinking in reverse kind of. I found I could blink fast enough that I could not see them, but that must have been at less than 1/4 second. Pretty amazing device the eye. At those light levels we only see black and white apparently, and nobody seems to know what an ISO speed equivalent for the eye might be, estimates run from 800 to 60,000. This is why I wonder about some of the astronauts saying they could not see the stars, and others say they could. I read that an ISS crewman had let his eyes adjust for 15 minutes, and then looking through a 1"x8" inch tube had counted stars, forget the numbers, but plenty. Here is another quote that stars could be seen, but barely. If I can stand by a bright light, or look directly at a bare bulb, and instantly see the stars, why does he need to be in total dark to see them?
Stars are not dramatically brighter in space (above the Earth's atmosphere). Professional astronomer and two-time space shuttle astronaut Ronald A. Parise stated that he could barely see stars at all from space. He had to turn out all of the lights in the shuttle to even glimpse the stars.[3]
The space station, even at its maximum height, still orbits within the ionosphere, with up to 10^6 electrons/c.c., so perhaps it is the electron density making the stars visible? The Lunar surface has been estimated at only 103/c.c so that might explain why some astronauts said they couldn't see stars form the Lunar surface? I'm enjoying reading David Parks book on light, still in the historical section, very interesting how light has been explained over the ages, some very clever, and very imaginative thinkers, but I'm hoping once I get to the 'meat', I may see something that fits in with my view of how light behaves, especially in the vacuum.
StevenJay
Re: Stars Are Thousands Of Times Closer Than They Appear
GaryN wrote: Here is another quote that stars could be seen, but barely. If I can stand by a bright light, or look directly at a bare bulb, and instantly see the stars, why does he need to be in total dark to see them? Stars are not dramatically brighter in space (above the Earth's atmosphere). Professional astronomer and two-time space shuttle astronaut Ronald A. Parise stated that he could barely see stars at all from space. He had to turn out all of the lights in the shuttle to even glimpse the stars.[3]
I haven't read this entire thread, so if this has already been kicked around, my appologies.
It seems to me that the common denominator here, regarding ISS personel and astronauts on the moon, is that they're all looking through glass.
Ever been in even a dimly-lit room at night with only the stars to illuminate the landscape outside? In my experience, not much of anything on the other side of the window is discernable. Once the interior lights are extinguished, though, some shapes and objects and even a few stars become visible. Remove the light-distorting glass barrier (step outside), and even more detail (including a sky full of stars) is able to be resolved.
Just my two pesos-worth.
GaryN
Re: Stars Are Thousands Of Times Closer Than They Appear
Ever been in even a dimly-lit room at night with only the stars to illuminate the landscape outside? In my experience, not much of anything on the other side of the window is discernable. Once the interior lights are extinguished, though, some shapes and objects and even a few stars become visible. Remove the light-distorting glass barrier (step outside), and even more detail (including a sky full of stars) is able to be resolved.
Well, it is not the glass that is the problem, I can see the stars much better when I wear my glasses! But yes, reflection when the light within a room is bouncing around must have some effect. Oblique light and destructive interference? Just guessing, but good point StevenJay, and I'll be doing some more crude experiments next time the stars are out. Have some polarised sunglasses, and some old camera lens filters kicking around somewhere.
fosborn
Re: Stars Are Thousands Of Times Closer Than They Appear
I wanted to post the specs on this picture with a stars background.
Date Acquired: May 6, 2010 Image Mission Elapsed Time (MET): 181616382 Instrument: Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS) WAC Filter: 2 (clear filter) Field of View: The WAC has a 10.5° field of view Images used to search for vulcanoids involve 10-second exposure times,
The multi-spectral MDIS has wide- and narrow-angle cameras (the "WAC" and "NAC," respectively) – both based on charge-coupled devices (CCDs), similar to those found in digital cameras http://messenger.jhuapl.edu/instruments/MDIS.html
A Multi-spectral image is one that captures image data at specific frequencies across the electromagnetic spectrum. The wavelengths may be separated by filters or by the use of instruments that are sensitive to particular wavelengths, http://en.wikipedia.org/wiki/Multi-spectral_Imaging
I cut a section from the pic in windows paint to show the stars.
X15_Photo_Stars.JPG
Aardwolf
Re: Stars Are Thousands Of Times Closer Than They Appear
fosborn wrote: I wanted to post the specs on this picture with a stars background.
Date Acquired: May 6, 2010 Image Mission Elapsed Time (MET): 181616382 Instrument: Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS) WAC Filter: 2 (clear filter) Field of View: The WAC has a 10.5° field of view Images used to search for vulcanoids involve 10-second exposure times,
The multi-spectral MDIS has wide- and narrow-angle cameras (the "WAC" and "NAC," respectively) – both based on charge-coupled devices (CCDs), similar to those found in digital cameras http://messenger.jhuapl.edu/instruments/MDIS.html
A Multi-spectral image is one that captures image data at specific frequencies across the electromagnetic spectrum. The wavelengths may be separated by filters or by the use of instruments that are sensitive to particular wavelengths, http://en.wikipedia.org/wiki/Multi-spectral_Imaging
I cut a section from the pic in windows paint to show the stars.
X15_Photo_Stars.JPG
This would be taken in our atmosphere so not really relevant to the earlier points.
fosborn
Re: Stars Are Thousands Of Times Closer Than They Appear
I believe filter 2 is the wide range filter so includes infra-red. Is there a comparable image through one of the visible range filters only?
why? Do you have a link to show this. The clear was specifically for imaging stars for navigation.
Spectral Filter Design. A 12-position multispectral filter wheel provides color imaging over the spectral range of the CCD detector (395-1040 nm). Eleven spectral filters are defined to cover wavelengths diagnostic of common silicate minerals and glasses and have full-width half maximum (FWHM) bandwidths from 5-40 nm. A broadband clear filter was included for optical navigation imaging of stars.
Re: Stars Are Thousands Of Times Closer Than They Appear
I tied to get more info on that(Earth, Moon, stars) image Frank, but no replies. The Messenger instruments are multispectral from IR to UV as far as I can determine, so what I believe we are seeing in this image is the UV fluorescence of molecular hydrogen. The image also shows the streaks from cosmic rays hittting the CCDs. If they take 4 images and subtract the objects that only show up in one image, then the streaks should not be there, but how many other objects would not be there? There is also the MASCS UV spectrometer and IR spectrograph, so I don't know what they are showing us. http://optics.org/news/2/3/27 @Aardwolf
This would be taken in our atmosphere so not really relevant to the earlier points.
Thats how I see it. The ionosphere is allowing the stars to be visible, to do with scattering of the X-ray light that is again, I belive, from florescence of elements in the 'stars' environs. I'll go right out on a limb and say that Earth based telescopes are not even seeing the stars, they are looking at the 3-d projection screen provided by the ionosphere, which is converting the incoming UV and X-ray emissions to visible wavelengths.
fosborn
Re: Stars Are Thousands Of Times Closer Than They Appear
GaryN wrote: The image also shows the streaks from cosmic rays hittting the CCDs. If they take 4 images and subtract the objects that only show up in one image, then the streaks should not be there, but how many other objects would not be there?
So are you saying they only took one image? I'm not sure what you telling me.
There is also the MASCS UV spectrometer and IR spectrograph, so I don't know what they are showing us?
I thought it was stated what camera they used. It was a CCD . Its a spectrometer only if the use the color filters?
Re: Stars Are Thousands Of Times Closer Than They Appear
So are you saying they only took one image? I'm not sure what you telling me.
I read that they normally take 4 consecutive 10 second images and then subtract the objects that do not show in all 4, so I don't know why the cosmic ray streaks are still there. That just made me wonder how many other objects would be eliminated using that method. Again Frank, I have had no success getting more details. If this is just from the CCD, then it could still be showing UV fluorescence, as most of the CCDs they use are 'back-thinned' to enhance UV sensitivity, and so operate as a spectrometer. As to whether these are electron multiplying CCDs (single photon sensitivity!), no idea.
fosborn
Re: Stars Are Thousands Of Times Closer Than They Appear
GaryN wrote:
So are you saying they only took one image? I'm not sure what you telling me.
I read that they normally take 4 consecutive 10 second images and then subtract the objects that do not show in all 4, so I don't know why the cosmic ray streaks are still there. That just made me wonder how many other objects would be eliminated using that method.
They are there because this is a single photo?
Again Frank, I have had no success getting more details. If this is just from the CCD, then it could still be showing UV fluorescence, as most of the CCDs they use are 'back-thinned' to enhance UV sensitivity, and so operate as a spectrometer. As to whether these are electron multiplying CCDs (single photon sensitivity!), no idea.
)
But yes, reflection when the light within a room is
