Actually, Cherenkov (I'm misspelling it) is caused by the radioactive decay particles going faster than the speed of light in the medium they're traveling in. It's analogous to the wake that a boat pushes in front of itself when traveling across water.
Before anyone says "you can't go faster than the speed of light", it is true that you can't go faster than the speed of light IN A VACUUM. But light doesn't travel quite as fast in air or any other material. This is the definition of the index of refraction.
I work at STScI and it sounds like they're going to be able to switch ACS back to the side 1 power supply. Unfortunately, it means that the WFC which is the most used won't be working. A failure of the side 1 supply to WFC is why they had to switch to side 2 this summer.
The good news is that WFPC2 is still working even if it doesn't have the imaging area or sensitivity of ACS. The telescope allocation committee just re-opened applications for next cycle so lots of people are just going to switch their proposals from using ACS to using WFPC2 (myself included). As a side note: anyone can apply for telescope time since its run with taxpayer money. Just go to the site and fill out the form.
The other good news is that the servicing mission is going ahead for early 2008 when they're going to put in WFPC3 which is a bit better than ACS and will have much lower distortions and a great new spectrograph called COS. That'll take HST to the end of its life in 2013. At that point, the next space telescope, JWST, will be launched. In case you're wondering though, JWST will have a much shorter life since it won't be possible to service it.
So yeah, it sucks that ACS smoked itself but it's not the end of the world.
I find the whole mostly-European "the best building material is stone or concrete" idea pretty funny. So far, I've owned two houses, both wood, and both old (the previous one was built in 1937, the one I currently live in was built in 1917). Both houses will last at least a hundred more years. Of course, it is true that if they were built of stone, they might last another 1000 years. It's hard to say, but regardless they're permanent structures. I have a feeling that this is much more about the types of home you grew up in rather than what the "best" building material actually is.
The other thing is that stone and brick are definitely not fireproof. You still need beams to support the floors and those are usually wood. Here in Baltimore there are a ton of brick row houses and they occasionally have terrible fires. A small fire starts inside and burns the furniture/floors/books/whatever and that ends up catching the beams on fire and you end up with an empty brick shell. Of course, since they're row houses, the fire ends up spreading through the brick walls to the neighboring houses and you lose 3 or 4 homes at once. Even though they're made of brick. Fire is a problem for everyone.
If you go look at the web page for the starfire optical range it clearly mentions the "Directed Energy Directorate's Starfire Optical Range". A large number of good observatories are at least partially funded by the Air Force... MRO in New Mexico is a perfect example. Regardless a lot of the information saying these things dates back to 1998 and 2001.
The Air Force also has some neat tricks up it sleeve doing optical interferometry (which is especially tricky since you really need to know the position of your mirrors to within the wavelength that you're working with). Last I heard though, that was limited by the fact that someone dropping a garbage can in the next room could throw things out of alignment.
There's one thing that people are overlooking too, it's great to be able to observe things with adaptive optics systems. I have another friend in astronomy who has actually been able to resolve stars using an Air Force system. The trick though is that stars aren't putting out enough energy to disrupt the atmosphere. If you suddenly start pumping enough energy through the atmosphere to destroy a satellite, you're going to do a lot of local heating and there's no way you could modify your beam fast enough to keep it nice and tight. You might as well use a non-adaptive telescope.
There are a few important things about the servicing mission. First of all, almost all of the parts are just sitting in a warehouse at the moment waiting to fly. The whole question about the servicing mission isn't a question of money, it's a question of whether the mission can be done safely without losing another shuttle.
As an astronomer, I can tell you that HST can do things that no other telescope can do. The Keck telescopes are bigger (frankly, there are lots of telescopes bigger, including the new 11m SALT telescope) and bigger telescopes can do spectroscopy faster (in some cases). But there is no ground-based telescope which can come close to HST in image quality... the atmosphere is just too tricky of a thing to look through. Plus, adaptive optics systems on the ground are really only effective in the near-IR and you can just give up on doing any UV work from the ground.
The "Hubble replacement" JWST that's going to launch next decade isn't really a Hubble replacement either. It's highly optimized to do infrared work and will have basically no optical capabilities. It'll definitely produce pretty pictures, but they're not going to be pictures of things you could see with your eyes and I think that's going to make it less powerful to the public.
Basically, if this servicing mission weren't to go forward, it would mean a pause in some of the most ground-breaking astronomical research for 5-10 years.
Well, this is what I do for my research, so I actually do know what I'm talking about.
The basic idea is that we know the shape of the point spread function of hubble extremely well. Since we do know that shape, it's fairly easy to do a cross-colloration and find positions to much better than single-pixel accuracy. Even from the ground it's pretty easy to get positions better than 1/10 of a pixel.
The thumb analogy used above is called parallax (which is often used to determine the distance to nearby stars) and that has absolutely nothing to do with how they found the velocities in this project. For this paper, they actually watched the stars move.
To reply to the previous comment, mass segregation should also occur in clusters of galaxies, especially the big rich clusters. Indeed, you often see supermassive elliptical galaxies in the center of clusters. The problem there is that the idea of equiparition of energy requires lots of 3-body gravitational interactions to equalize the energy of all the various objects. In globular clusters, this happens on short timescales (the timescale might be only 500 million years.:) ) In galactic clusters, you might only get one interaction every billion years so you have to wait a lot longer to see the results.
It's actually an equiparition of energy thing. Due to all of the gravitational interactions that occur in the cluster, all of the stars should have the same total energy (potential + kinetic). Therefore, at a given area in the cluster, the heavier stars (which are around.80 solar masses) should be moving slower than the lighter stars (which are.2 to.4 solar masses).
The amazing thing is that they were able to determine this by measuring 1/100th of a pixel shifts in Hubble images. Needless to say, it's hard to do astrometry that precisely.
Slashdot Mirror
Actually, Cherenkov (I'm misspelling it) is caused by the radioactive decay particles going faster than the speed of light in the medium they're traveling in. It's analogous to the wake that a boat pushes in front of itself when traveling across water.
Before anyone says "you can't go faster than the speed of light", it is true that you can't go faster than the speed of light IN A VACUUM. But light doesn't travel quite as fast in air or any other material. This is the definition of the index of refraction.
I work at STScI and it sounds like they're going to be able to switch ACS back to the side 1 power supply. Unfortunately, it means that the WFC which is the most used won't be working. A failure of the side 1 supply to WFC is why they had to switch to side 2 this summer.
The good news is that WFPC2 is still working even if it doesn't have the imaging area or sensitivity of ACS. The telescope allocation committee just re-opened applications for next cycle so lots of people are just going to switch their proposals from using ACS to using WFPC2 (myself included). As a side note: anyone can apply for telescope time since its run with taxpayer money. Just go to the site and fill out the form.
The other good news is that the servicing mission is going ahead for early 2008 when they're going to put in WFPC3 which is a bit better than ACS and will have much lower distortions and a great new spectrograph called COS. That'll take HST to the end of its life in 2013. At that point, the next space telescope, JWST, will be launched. In case you're wondering though, JWST will have a much shorter life since it won't be possible to service it.
So yeah, it sucks that ACS smoked itself but it's not the end of the world.
I find the whole mostly-European "the best building material is stone or concrete" idea pretty funny. So far, I've owned two houses, both wood, and both old (the previous one was built in 1937, the one I currently live in was built in 1917). Both houses will last at least a hundred more years. Of course, it is true that if they were built of stone, they might last another 1000 years. It's hard to say, but regardless they're permanent structures. I have a feeling that this is much more about the types of home you grew up in rather than what the "best" building material actually is.
The other thing is that stone and brick are definitely not fireproof. You still need beams to support the floors and those are usually wood. Here in Baltimore there are a ton of brick row houses and they occasionally have terrible fires. A small fire starts inside and burns the furniture/floors/books/whatever and that ends up catching the beams on fire and you end up with an empty brick shell. Of course, since they're row houses, the fire ends up spreading through the brick walls to the neighboring houses and you lose 3 or 4 homes at once. Even though they're made of brick. Fire is a problem for everyone.
If you go look at the web page for the starfire optical range it clearly mentions the "Directed Energy Directorate's Starfire Optical Range". A large number of good observatories are at least partially funded by the Air Force... MRO in New Mexico is a perfect example. Regardless a lot of the information saying these things dates back to 1998 and 2001. The Air Force also has some neat tricks up it sleeve doing optical interferometry (which is especially tricky since you really need to know the position of your mirrors to within the wavelength that you're working with). Last I heard though, that was limited by the fact that someone dropping a garbage can in the next room could throw things out of alignment. There's one thing that people are overlooking too, it's great to be able to observe things with adaptive optics systems. I have another friend in astronomy who has actually been able to resolve stars using an Air Force system. The trick though is that stars aren't putting out enough energy to disrupt the atmosphere. If you suddenly start pumping enough energy through the atmosphere to destroy a satellite, you're going to do a lot of local heating and there's no way you could modify your beam fast enough to keep it nice and tight. You might as well use a non-adaptive telescope.
There are a few important things about the servicing mission. First of all, almost all of the parts are just sitting in a warehouse at the moment waiting to fly. The whole question about the servicing mission isn't a question of money, it's a question of whether the mission can be done safely without losing another shuttle.
As an astronomer, I can tell you that HST can do things that no other telescope can do. The Keck telescopes are bigger (frankly, there are lots of telescopes bigger, including the new 11m SALT telescope) and bigger telescopes can do spectroscopy faster (in some cases). But there is no ground-based telescope which can come close to HST in image quality... the atmosphere is just too tricky of a thing to look through. Plus, adaptive optics systems on the ground are really only effective in the near-IR and you can just give up on doing any UV work from the ground.
The "Hubble replacement" JWST that's going to launch next decade isn't really a Hubble replacement either. It's highly optimized to do infrared work and will have basically no optical capabilities. It'll definitely produce pretty pictures, but they're not going to be pictures of things you could see with your eyes and I think that's going to make it less powerful to the public.
Basically, if this servicing mission weren't to go forward, it would mean a pause in some of the most ground-breaking astronomical research for 5-10 years.
Well, this is what I do for my research, so I actually do know what I'm talking about.
The basic idea is that we know the shape of the point spread function of hubble extremely well. Since we do know that shape, it's fairly easy to do a cross-colloration and find positions to much better than single-pixel accuracy. Even from the ground it's pretty easy to get positions better than 1/10 of a pixel.
The thumb analogy used above is called parallax (which is often used to determine the distance to nearby stars) and that has absolutely nothing to do with how they found the velocities in this project. For this paper, they actually watched the stars move.
To reply to the previous comment, mass segregation should also occur in clusters of galaxies, especially the big rich clusters. Indeed, you often see supermassive elliptical galaxies in the center of clusters. The problem there is that the idea of equiparition of energy requires lots of 3-body gravitational interactions to equalize the energy of all the various objects. In globular clusters, this happens on short timescales (the timescale might be only 500 million years. :) ) In galactic clusters, you might only get one interaction every billion years so you have to wait a lot longer to see the results.
It's actually an equiparition of energy thing. Due to all of the gravitational interactions that occur in the cluster, all of the stars should have the same total energy (potential + kinetic). Therefore, at a given area in the cluster, the heavier stars (which are around .80 solar masses) should be moving slower than the lighter stars (which are .2 to .4 solar masses).
The amazing thing is that they were able to determine this by measuring 1/100th of a pixel shifts in Hubble images. Needless to say, it's hard to do astrometry that precisely.