Imaging with the shutter closed measures a different source of noise known as dark current (thermal noise of the ccd will cause a small number of free electrons rather than those freed by incoming photons). This noise is proportional to the length of the exposure, unlike readout noise which is a single constant factor.
As far as I know (I'm just a theorist), it is impossible to remove readout noise, since it is affected by the actual distribution of electrons on the ccd image. Someone who actually deals with astronomical imaging should feel free to correct me here.
As the previous poster noted, there isn't any atmosphere and thus the technique isn't useful for HST.
Additionally, while they don't mention details in the article, I presume they have a specially designed camera. This is an old technique, but it's generally limited to very bright objects due to something called readout noise. Basically all CCD's produce an additional signal due to the process of reading out the data. This limits the effectiveness of repeated short observations to sources which are much brigher than this noise, since the noise also grows linearly with the number of images taken.
To image distant galaxies you typically have to take exposures of one to several hours, and thus this technique isn't useful.
It's interesting how people's tastes differ so much. I couldn't disagree more about thumb trackballs. I had an early Microsoft trackball (not the explorer, not sure what it was) and couldn't stand it. Using my index finger to move the ball put my wrist at a very uncomfortable angle. My Logitech trackman, however, allows my hand to sit extremely comfortably and only my thumb need move, and that at the natural angle and range of motion.
Pelosi would not become vice-president, she's simply 3rd in line after both the President and Vice-President are gone. How do you think Ford became president? Agnew was impeached, then Nixon appointed Ford, who became president when Nixon resigned.
The point is that if it's technically feasible, then you would launch specialized military satellites designed to find subs in real-time rather than using publically available data.
No, you probably won't find technical details in these sources, but many of them contain links to more detailed information.
Also, as much as I find your dismissive attitude obnoxious, I am happy to help you explore the actual evidence for dark matter. Feel free to reply to this post with any actual questions.
Dark matter has vast (let me repeat, VAST) amounts of evidence beyond rotation curves of galaxies. It is supported by weak and strong gravitational lensing measurements, the clustering of galaxies, flucutations in the cosmic microwave background, hot gas and random motions of galaxies in galaxy clusters...
All of this evidence is sufficient to say that either 1) dark matter exists or 2) our theory of gravity is broken in exactly the way necessary to seem like there's dark matter when there really isn't. #1 is the simplest, and as of yet, nobody has found a #2 that even comes close (although people are working on trying to find one). Cold dark matter has overcome nearly 40 years of people trying to poke holes in it, and it's stood the test of time.
In addition, it's not the kludge solution as it is portrayed by so many here on slashdot. There are good particle physics reasons to expect a heavy weakly interacting non-relativistic particle. Just because we don't know exactly what it is yet does not mean it's not a good theory.
We're already searching for dark matter annihilation signatures in the centers of dwarf galaxies, and we have direct detection experiments running here on Earth. So called direct detection of dark matter may only be years away. At the minimum we continually rule out parameter space of theories that do fit the observations, refining our understanding of what signatures to look for.
Okay, that's an interesting thought, but it takes 2 seconds to read the article and see that the plane of satellites is not in the plane of Andromeda's disk, in fact they are perpendicular, so if anything it contradicts Cooperstock's model.
Interestingly, the Milky Way satellites are also in a plane, which caused a bit of a flap about a year or so ago, as everyone expected the dark matter subhalos (the hosts of satellite galaxies) to be isotropic.
My advisor wrote a paper, however, which demonstrates that the subhalo distribution is anisotropic, and when you select the ones that are likely to be luminous (some are too small to cool and make stars), their distribution is consistent with the Milky Way's satellites. (http://arxiv.org/abs/astro-ph/0502496)
The current consensus is that the paper is fundamentally flawed, and that when done correctly non-linearities from GR cannot explain the flat rotation curves of spiral galaxies (not to mention the vast amounts of other evidence for dark matter including hot gas in galaxy clusters, fluctuations in the cosmic microwave background, strong lensing arcs in clusters, weak gravitational lensing by galaxies, the distribution of galaxies on large scales, etc).
Unfortunately, the general public only hears about the initial press release, not the work of many other scientists in debunking those results.
The last I heard about that paper it had a major flaw in that it effectively predicted the existence of an infinitely thin, infinite mass sheet perpendicular to the rotation axis of the galaxy (thus causing the constant rotation).
Besides, this paper hardly explains the vast number of other observations which support the existence of dark matter (acoustic peaks in the cosmic microwave background, velocity dispersion of galaxies in clusters, weak and strong gravitational lensing measurements, spatial distribution of galaxies, etc).
That's not to say that it's not possible that there is no dark matter, and that we just need to modify our theory of gravity, however nobody has come up with a modification which fits all current observations.
Knowledge is simply not as important as it once was. Most things worth knowing are easily accessible through information tools. The ability to use these tools to locate and process complex information and apply it is far more important.
While clearly not susceptible to ovarian cancer (perhaps comparable to prostate and testicular cancers), men do suffer from breast cancer, albeit at a lower rate than women.
If you look at the Chicago pictures, it shows Soldier Field under construction. Demolition began after the 2001 season, and the image looks like it's just starting the new construction, which happened in early 2002). So that gives roughly a year time frame for these pictures.
Meigs field is also still there, and the building I live in is just beginning construction (it was finished in late 2003 I believe).
No, that's absolutely incorrect. When scientists talk about dark matter they really do mean some actual stuff, not just a problem with gravity. We do have plenty of reason to believe in this magical material (too many for me to list here in fact, short list of acronym soup: BBN, CMB, LSS).
There are quite a few models for what dark matter could be, many motivated by our theories of particle physics.
If you want to learn more, here is an excellent review on the subject, written at a very basic level.
Essentially all you need is a massive particle with a very low probability of reaction (cross section). There are people who are trying to use techniques similar to neutrino detection to find evidence of actual dark matter particles (come back in 5-10 years and we may have detected dark matter particles).
We may also be able to see gamma rays from dark matter particle annihilation at the center of our galaxy, or at the centers of dwarf satellite galaxies (the Milky way may be difficult, the signal would be higher, but you also have confusion with other high-energy sources).
Ok, the cd upgrade path is all well and good, but what do you do when you're in Chicago, USA and the server is in Paris, France?
A network upgrade is just out of the question (too many things can go wrong).
We were perfectly happy paying Redhat $60/server for simple security updates, that's all we ever wanted, but they decided they didn't want our business.
Generally the applications you run on a supercomputer are dedicated (i.e. one process should get all of the CPU except when doing I/O and other kernel operations). Because of this, any scheduler should be able to do as well as any other, so there's no reason to change to a new kernel.
Of course, changing the kernel might get you slightly better drivers and improve I/O performance, and perhaps memory allocation, but the linux 2.4 kernel was mature enough that I doubt there are any significant improvements for the type of jobs they run (CPU not I/O bound).
Well the rest mass of a single star (say the same mass as the sun) is 2x10^33 * (3x10^10)^2 ergs ~ 1.8x10^54 ergs. In this post the energy of these objects is estimated at 2x10^52 ergs, so the rest mass of a single star is 90 times one of these objects, and there are on the order of 10^10 stars per galaxy. So before we even discuss dark matter you'd need a hell of a lot of these objects to have greater energy than just the visible stars in our galaxy.
Slashdot Mirror
Imaging with the shutter closed measures a different source of noise known as dark current (thermal noise of the ccd will cause a small number of free electrons rather than those freed by incoming photons). This noise is proportional to the length of the exposure, unlike readout noise which is a single constant factor.
As far as I know (I'm just a theorist), it is impossible to remove readout noise, since it is affected by the actual distribution of electrons on the ccd image. Someone who actually deals with astronomical imaging should feel free to correct me here.
Doug
Actually that would be a terrible idea. You can't have effective oversight if your funding is controlled by the party you are overseeing.
Doug
As the previous poster noted, there isn't any atmosphere and thus the technique isn't useful for HST.
Additionally, while they don't mention details in the article, I presume they have a specially designed camera. This is an old technique, but it's generally limited to very bright objects due to something called readout noise. Basically all CCD's produce an additional signal due to the process of reading out the data. This limits the effectiveness of repeated short observations to sources which are much brigher than this noise, since the noise also grows linearly with the number of images taken.
To image distant galaxies you typically have to take exposures of one to several hours, and thus this technique isn't useful.
Doug
It's interesting how people's tastes differ so much. I couldn't disagree more about thumb trackballs. I had an early Microsoft trackball (not the explorer, not sure what it was) and couldn't stand it. Using my index finger to move the ball put my wrist at a very uncomfortable angle. My Logitech trackman, however, allows my hand to sit extremely comfortably and only my thumb need move, and that at the natural angle and range of motion.
Pelosi would not become vice-president, she's simply 3rd in line after both the President and Vice-President are gone. How do you think Ford became president? Agnew was impeached, then Nixon appointed Ford, who became president when Nixon resigned.
Doug
The point is that if it's technically feasible, then you would launch specialized military satellites designed to find subs in real-time rather than using publically available data.
You can have firefox clear everything when it starts up as well which fixes the crash problem.
5. Driver hits same bug that caused first instance to crash.
6. Goto 1
It's quarters all the way up....
No, I didn't give any supporting links because I wouldn't know where to begin...
h tmld ark.htmlo de2.html#SECTION00020000000000000000
We're talking about thousands of scientific papers going back to the 1930's....
Instead, here are some links to some non-technical introductions:
http://map.gsfc.nasa.gov/m_uni/uni_101matter.html
http://astron.berkeley.edu/~mwhite/darkmatter/dm.
http://pancake.uchicago.edu/~carroll/cfcp/primer/
http://www.astro.princeton.edu/~dns/MAP/Bahcall/n
http://zebu.uoregon.edu/text/darkmatter.txt
No, you probably won't find technical details in these sources, but many of them contain links to more detailed information.
Also, as much as I find your dismissive attitude obnoxious, I am happy to help you explore the actual evidence for dark matter. Feel free to reply to this post with any actual questions.
Doug
Dark matter has vast (let me repeat, VAST) amounts of evidence beyond rotation curves of galaxies. It is supported by weak and strong gravitational lensing measurements, the clustering of galaxies, flucutations in the cosmic microwave background, hot gas and random motions of galaxies in galaxy clusters...
All of this evidence is sufficient to say that either 1) dark matter exists or 2) our theory of gravity is broken in exactly the way necessary to seem like there's dark matter when there really isn't. #1 is the simplest, and as of yet, nobody has found a #2 that even comes close (although people are working on trying to find one). Cold dark matter has overcome nearly 40 years of people trying to poke holes in it, and it's stood the test of time.
In addition, it's not the kludge solution as it is portrayed by so many here on slashdot. There are good particle physics reasons to expect a heavy weakly interacting non-relativistic particle. Just because we don't know exactly what it is yet does not mean it's not a good theory.
We're already searching for dark matter annihilation signatures in the centers of dwarf galaxies, and we have direct detection experiments running here on Earth. So called direct detection of dark matter may only be years away. At the minimum we continually rule out parameter space of theories that do fit the observations, refining our understanding of what signatures to look for.
Doug
Okay, that's an interesting thought, but it takes 2 seconds to read the article and see that the plane of satellites is not in the plane of Andromeda's disk, in fact they are perpendicular, so if anything it contradicts Cooperstock's model.
Interestingly, the Milky Way satellites are also in a plane, which caused a bit of a flap about a year or so ago, as everyone expected the dark matter subhalos (the hosts of satellite galaxies) to be isotropic.
My advisor wrote a paper, however, which demonstrates that the subhalo distribution is anisotropic, and when you select the ones that are likely to be luminous (some are too small to cool and make stars), their distribution is consistent with the Milky Way's satellites. (http://arxiv.org/abs/astro-ph/0502496)
Doug
The current consensus is that the paper is fundamentally flawed, and that when done correctly non-linearities from GR cannot explain the flat rotation curves of spiral galaxies (not to mention the vast amounts of other evidence for dark matter including hot gas in galaxy clusters, fluctuations in the cosmic microwave background, strong lensing arcs in clusters, weak gravitational lensing by galaxies, the distribution of galaxies on large scales, etc).
Unfortunately, the general public only hears about the initial press release, not the work of many other scientists in debunking those results.
Doug
The last I heard about that paper it had a major flaw in that it effectively predicted the existence of an infinitely thin, infinite mass sheet perpendicular to the rotation axis of the galaxy (thus causing the constant rotation).
Besides, this paper hardly explains the vast number of other observations which support the existence of dark matter (acoustic peaks in the cosmic microwave background, velocity dispersion of galaxies in clusters, weak and strong gravitational lensing measurements, spatial distribution of galaxies, etc).
That's not to say that it's not possible that there is no dark matter, and that we just need to modify our theory of gravity, however nobody has come up with a modification which fits all current observations.
Doug
I think you should have charged $0.03 for that information.
Doug
http://www.google.com/search?q=creating+fire+with+ sticks/
Knowledge is simply not as important as it once was. Most things worth knowing are easily accessible through information tools. The ability to use these tools to locate and process complex information and apply it is far more important.
Doug
Of course you know AMD has already done just that.
You don't actually think they'd challenge Intel to a contest they would lose, do you?
Doug
While clearly not susceptible to ovarian cancer (perhaps comparable to prostate and testicular cancers), men do suffer from breast cancer, albeit at a lower rate than women.
Doug
Unfortunately it appears you'll never get to step 6 due to the infinite loop of step 5.
The reverse is very common as well. My wife and I broke up a week before we got engaged.
Sometimes you just need something drastic to force the issue one way or the other.
Doug
If you look at the Chicago pictures, it shows Soldier Field under construction. Demolition began after the 2001 season, and the image looks like it's just starting the new construction, which happened in early 2002). So that gives roughly a year time frame for these pictures.
Meigs field is also still there, and the building I live in is just beginning construction (it was finished in late 2003 I believe).
Doug
No, that's absolutely incorrect. When scientists talk about dark matter they really do mean some actual stuff, not just a problem with gravity. We do have plenty of reason to believe in this magical material (too many for me to list here in fact, short list of acronym soup: BBN, CMB, LSS).
There are quite a few models for what dark matter could be, many motivated by our theories of particle physics.
If you want to learn more, here is an excellent review on the subject, written at a very basic level.
Essentially all you need is a massive particle with a very low probability of reaction (cross section). There are people who are trying to use techniques similar to neutrino detection to find evidence of actual dark matter particles (come back in 5-10 years and we may have detected dark matter particles).
We may also be able to see gamma rays from dark matter particle annihilation at the center of our galaxy, or at the centers of dwarf satellite galaxies (the Milky way may be difficult, the signal would be higher, but you also have confusion with other high-energy sources).
Doug
Ok, the cd upgrade path is all well and good, but what do you do when you're in Chicago, USA and the server is in Paris, France?
A network upgrade is just out of the question (too many things can go wrong).
We were perfectly happy paying Redhat $60/server for simple security updates, that's all we ever wanted, but they decided they didn't want our business.
Doug
Generally the applications you run on a supercomputer are dedicated (i.e. one process should get all of the CPU except when doing I/O and other kernel operations). Because of this, any scheduler should be able to do as well as any other, so there's no reason to change to a new kernel.
Of course, changing the kernel might get you slightly better drivers and improve I/O performance, and perhaps memory allocation, but the linux 2.4 kernel was mature enough that I doubt there are any significant improvements for the type of jobs they run (CPU not I/O bound).
Doug
Well the rest mass of a single star (say the same mass as the sun) is 2x10^33 * (3x10^10)^2 ergs ~ 1.8x10^54 ergs. In this post the energy of these objects is estimated at 2x10^52 ergs, so the rest mass of a single star is 90 times one of these objects, and there are on the order of 10^10 stars per galaxy. So before we even discuss dark matter you'd need a hell of a lot of these objects to have greater energy than just the visible stars in our galaxy.
Doug