Become a fan of Slashdot on Facebook

 


Forgot your password?
Close
typodupeerror
×
Space Science

Dirt Cheap Telescopes With Liquid Mercury 161

Posted by Hemos from the who-gets-to-be-the-mad-hatter dept.
Decibel writes "Scientists at the University of British Columbia have built a 6 meter telescope that uses a plate filled with mercury for its primary mirror. At a cost of $1 million, this technology makes it possible for many research teams to have continuous access to a telescope, rather than sharing with many other researchers. On a somewhat related note, the top 10 images taken by the only company that provides commercial satellite images at 1 meter resolution have been released to the public. Included are pics of the Olympic Park in Sydney, the Hollywood sign, Hoover Dam, and the Great Pyramids of Egypt. I don't know how they determined that these were the top 10, but they're certainly worth a look."

Personal addendum by jamie .

Summer 1983: I was at a cool kids' summer camp learning about astronomy. I was 12. A friend and I came up with the idea of spinning mercury into mirrors. We didn't know much about optics or physics and had no idea if it would work, but we presented the idea to the Very Smart guest speaker the next day.

He thought about it for a second, and shot us down: he didn't think it would focus properly because the surface would be a catenary, not parabolic.

I would just like to take this opportunity to say: in your face, dude.

Mercury mirrors do not, however, make good replacements for general-purpose telescopes. They only point straight up; they'll never do long exposures or see anything outside their latitude. I'm a little surprised the article doesn't emphasize this.

(On the off-chance my "co-inventor" Bill Hall, from Kalamazoo, Michigan is reading this: drop me a line, Bill.)
This discussion has been archived. No new comments can be posted.

Dirt Cheap Telescopes With Liquid Mercury More

Dirt Cheap Telescopes With Liquid Mercury

Comments Filter:

  • My God! (Score:1)

    by Luke ( 7869 )
    THIS HAS ALREADY BEEN POSTED!

    I remember reading about Mercury telescopes within the past week.

    Lame.
  • Doh! Sorry, the star stayed still still. The mercury was rippling... someone bumped into the telescope again.

    Stephen! Quit dancing!
  • ...at UBC...

    This always has been a great research university. If only the provincial government hadn't backed out of the proposed KAON upgrade to the TRIUMF particle accelerator, we'd have some kick-ass particle physics happening here, too. Oh well, at least we still have the biggest cyclotron around.

    Anyway, now that I'm done bragging, I thought I'd post a link [astro.ubc.ca] to more info about the telescope. Enjoy!

  • Re:BWARHARHAR~! (Score:1)

    by Anonymous Coward
    While your argument is salient and concise as usual, you have failed to miss the most cogent of points made. for instance, while here, you say:

    bytui by&*BY UP BYP Byuie yuiew byutiewq buia BYUI BYUPIb yewuia gyueriwq ytu4iq hejkwq hr3jmq, hjkLB HGJL HJKLf bndsndsa bhjwoqb ryuiqwpb yytheiwq; thuiby y98234p yrtu34293291 b598p yru33p9 byr89pewq9pwq yrtyrt9843qp

    you very nearly immediately countermand your own argument with this statement:

    kwqlbfnefnerwjqewjq bhbhfgjekwekwlq hfgfiwq hgkjl bnvcm ncm,xhbvjklK HKJL HI Ufghdsuia; yuiea YU^&(^&*)^&*(G^G^ &*SAB Yfheil ahttrewliqrewlq n ntewjkqewjkqlewql h;iweq

    I think it might be that in trying to convey some of the subtleties of the various facets of the quandry, you've simply managed to outwit yourself.

    I do think you nearly managed to save it with your summation, though.

    s l a s h d o t - s u x !

    Bravo, and well said!

    See you on the next thread,

    Cecil B Demille
  • I sware that looks like a screenshot to simcity nthousand.
  • The other day, I was getting bored and would like to scan the sky in the evening, so I thought maybe I should get a telescope. I went to Fry's and saw some big ones with price tag in the 1000's and I thought that was expensive.

    And now you people just told me a price tag of one mil is "dirt cheap".

    Gee, I thought I have been living on planet Earth....

  • Why aren't there any commercial satellites that would provide military-class resolution?

    Is this technology restricted?

  • Wouldn't this be a bit dangerous---seeing the properties of Mercury? Its bad enough that they use Liquid Mercury in some thermometers, but the amount required for a mirror of this size could be a huge environmental health hazard if anything ever happened.

    If it weren't for that fact, I'd be all for it. I have no problem with cheap telescopes...but they need to be safe enough not to worry about killing the entire population of the town its located in.

    -Julius X
  • Looking at the one-meter photos got me thinking. What if we had a series of shots like this of a crime scene? You could probably make out the color of a car and its general shape on a one-half meter photo. This could be another tool for prosecuting high profile criminal cases. Maybe someday a prosecutor will be able to say to a jury, "we have a satellite photo of a brown truck at the crime scene and a photo of the defendant's driveway with no brown truck even though he says he was home." The evidence would be circumstantial, so you couldn't convict anybody with just a satelite picture. Still, it would be effective for casting doubt on shaky alibis.
  • Caveat: IANAA(stronomer)

    If the main telescope mirror has to be flat, why can't light be "piped" onto it by targetable accessory mirrors? Is there some reason that an apparatus of optically flat mirrors couldn't be used, in place of conventional telescopes where the whole thing moves? My only thought is that maybe the light would be diminished by being bounced around, and so maybe very dim objects couldn't be seen as well. And the accessory mirrors wouldn't require as massive a mount to hold them in place, would they?

  • The problems with the mercury telescope (Score:3)

    by ErfC ( 127418 ) on Tuesday September 26, 2000 @08:06AM (#752808) Homepage
    As one of my profs once said, "There are two problems with the mercury telescope. It can only point straight up. And the fumes make you go maaaaad."

    -Erf C.
  • First, way to go jamie. Too bad you didn't apply for a patent. :)

    Second, I'm a little troubled by scientists who don't like to share telescopes. I could understand if it's a simple time issue (e.g. all of the good telescopes are booked up). At the same time, it does not speak well of the scientific community if it's members are adopting an attitude of, "This telescope is mine! Mine! Get your own!"

    At one time, I thought that the physical sciences were the last example of true community cooperation for the good of everyone. Today, however, science is becoming corporatized and dominated by a famous few. The rush to get patents and "lock-in" advancements in knowledge (as in the Genome project) is only slightly more shameful than the mad rush of scientists to be first to publish a discovery.

    Make no mistake, there are serious egos involved here. Unlike Slashdot, a "first post" in the astronomy community means good karma -- fame and grants for further study. The fact that it may improve the scientist's standard of living is a bit of a hush-hush secret.

    Is the increasing capitalization of science really a good thing? In the words of Bloom County's Oliver, "Even research physicists need Porsches."
  • Actually, a little-known fact is that the Pentagon, the NSA, and their non-US equivalents actually give out all their most secret R&D for free! Yes! For free! Anyone can have it! Go ahead, take some!

    So, yes, I find it very puzzling that nobody's launched one yet.

    Bruce

  • I don't know how they determined these were the top 10

    They're a commercial company. They sell satellite pictures. How the hell do you think they figured out which were their top ten sellers? Maybe they looked at their own sales figures? Nah, too easy.

    As for the guy thinking about crime scene tools - the satellites don't cover the entire world every 15 minutes you know. What good is a picture of the crime scene if the last time it was covered by a satellite and there wasn't a cloud cover was 6 months ago?
  • This University of British Columbia telescope costs about $1 million. A conventional telescope with a regular solid glass mirror of the same size would require an outlay of about $100 million.


    Clever use of simple physics, but how does this still cost $1 million? I'm sure the mercury will cost a little (and I'd certainly keep a lid on it, dunno how they're handling that) and they air cushion could be done with stuff from the surplus shop... what else?

    On a somewhat related note, the top 10 images taken by the only company that provides commercial satellite images at 1 meter resolution have been released to the public. Included are pics of the Olympic Park in Sydney, the Hollywood sign, Hoover Dam, and the Great Pyramids of Egypt. I don't know how they determined that these were the top 10, but they're certainly worth a look."


    What? Not a topdown look at Natalie Portman [natalieportman.com]? Perverts!


    --
    Chief Frog Inspector
  • Like the corporate world couldn't come up with funding and brains to achieve the same?
  • A military quality satellite actually has a lot to do with a high-quality ground based telescope. The best ground-based scopes have approximately 1 micro-degree resolution, right? IIRC, that works out to about 1cm resolution from low-earth orbit. So, given that these things cost US$100 million on the ground, how much do you think it would cost to put up a satellite with the same capabilities? I'm thinking a cool US$1 billion or so. That's why the military is the only one who can afford satellites that can tell the difference between sneakers and wingtips from 100 miles us. Be happy that you've got a company with enough guts to put a commercial telescope of any kind up there.

    Walt
  • "This four-meter color image features downtown San Francisco and the landmark Transamerica Building. Space Imaging's Ikonos satellite collected the image October 21, 1999."

    They should be careful with that image of Sanfrancisco. Trans America doesn't like people taking unauthorized pictures of their building and selling them. even if it is from outer space. It IS trademarked after all...

    xoxo
    freq

  • Jamie writes, "Mercury mirrors do not, however, make good replacements for general-purpose telescopes. They only point straight up; they'll never do long exposures or see anything outside their latitude. I'm a little surprised the article doesn't emphasize this."

    Yeah, maybe on Earth... Mercury mirrors could be applied in space, as well. You just need a method to control the "film" of mercury that you're using as the mirror - where "up" and "down" have no meaning.

  • you lowered the temperature of the mercury to less then 25C (freezing point of mercury) as it is spinning. It should have the exact same shape as when it was liquid. Plus, you wouldn't have to spin it after it was frozen.
  • The HIPAS [alaska.edu] observatory operated near Fairbanks AK by UCLA has had a 2.7 m mercury telescope operating as part of their LIDAR system for well over a year (I couldn't find a first light date easily, so that's a very conservative number--I think it's been two or three years at least). Sure a 6m 'scope will be sweet. But if /. is going to start updating me with every new larger telescope that comes out...
  • My only thought is that maybe the light would be diminished by being bounced around, and so maybe very dim objects couldn't be seen as well

    Bingo, you got it. 100% reflectivity mirrors are the Holy Grail. A high reflectivity mirror now is insanely expensive to make at a decent size.

    You're idea is good, but the economics of it dictate that to do it would be just as expensive as building a big honkin' scope anyway.

  • Which statement sounds right to you:

    1. GE will spend billions of dollars to see from space what brand of shirt I'm wearing.
    2. a bunch of overfunded paranoid spies will spend billions of dollars to see from space what brand of shirt I'm wearing.

    Honestly, you couldn't have figured this out on your own?

    Bruce

  • You get what you pay for / It may be worth it (Score:4)

    by GSearle ( 40628 ) on Tuesday September 26, 2000 @08:17AM (#752821) Homepage
    This poses some interesting problems, along with some possibilities as well.

    First of all, you can't point it. It has to point straight up! But what do you want for the price? They might be able to make a movable target like the one on the Arecibo dish, but then you still only get a few degrees of pointability. For the price, though, you could build lots of them and plant them at different latitudes, essentially getting full-sky coverage as the Earth turns. Now all we need is a little artificial gravity...

    Mercury is toxic and it evaporates. They mentioned a "resin coating" in the article. Perhaps this solves the evaporation problem. How do they keep miniscule air currents from causing even the littlest ripple? The platform is spinning, which will cause some air turbulence.

    Hey, I wonder if "adaptive optics" could be applied to this? It is a flexible surface. How could this be done? Electric currents and magnetic fields, perhaps?

  • It's the largeness of the mirrors/lenses that give a really big telescope it's power. The larger that the mirror/lens is the more light that the telescope can gether and the better it is at picking out dim/small objects. I think that the problem with using accessory mirrors to direct light to the main mirror is the result of the fact that the first mirror/lens is what really determines how good the telescope is. While I'd imagine that building a really large flat mirror would be a little easier than building a really large curved mirror, you would still be left with the problem of making a really large and really perfect mirror. It's the cost of such a mirror that this project is attempting to eliminate.
    ________________
    They're - They are
    Their - Belonging to them
  • Forgot to mention... Jamie writes, "Mercury mirrors do not, however, make good replacements for general-purpose telescopes. They only point straight up; they'll never do long exposures or see anything outside their latitude. I'm a little surprised the article doesn't emphasize this. "

    Umm, since when are mirrors responsible for exposures in the first place? That's a function of whatever imaging equipment you hook up to the telescope (i.e. camera) and not the mirror, or the telescope itself.

    Also, normal telescopes don't "see anything outside their lattitude" either. Last time I checked, they don't move any more than mercury-based mirrors do. ;>

  • The vapor pressure of mercury is very low, so it should be ok under normal operation. However, I wonder what their scenario is in case of a fire.

  • Re:Is sharing so bad? (Score:3)

    by ptomblin ( 1378 ) <ptomblin@xcski.com> on Tuesday September 26, 2000 @08:19AM (#752825) Homepage Journal
    First, way to go jamie. Too bad you didn't apply for a patent. :)

    Nice try, but according to the referenced article:

    The concept of LMTs can be mapped back to the 18th century. Experiments that utilized the concept were conducted in the 1800s and the early 1900s, but the results were disappointing.

    A little hard to patent a technology that is dead obvious (yes, I thought of the same idea when I was a kid too) and has been experimented with since long before you were born. Unless it's software rather than technology, in which case the patent office will grant you a patent immediately. :-)
  • Mostly I want to see the 10 images. Somehow, that link, and the links on that page, don't show show me anything. Hmmm.

  • Take a look at these:

    Is it just me, or does picture number 1 [spaceflightnow.com] look like a screen shot from SimCity? =)

    What about picture number 6 [spaceflightnow.com] then, looks like a screen shot from a scifi movie :-)

    No "civilan targets" were destroyed... yeah right compare the pics before [spaceflightnow.com] and after [spaceflightnow.com] the war in Chechenya

  • My impression of the community around telescopes is that the scientists are generally pretty good about sharing resources. The problem is that when the resources are very expensive the high costs have to be shared as well and to make this practical, they have to be shared between a large number of projects.

    To make a really bad analogy, it's not so bad to have to share a car with your little sister, but you'd like it a whole lot better if you didn't have to. If someone found a way to make a car that's almost as good for 1% of the cost, then you would probably be able to get your own. And having your own is a good thing(tm).
    ________________
    They're - They are
    Their - Belonging to them

  • How stupid does a company look when it doesn't give the URL of its own web site in a news release that mentions it? Here's the main site [spaceimaging.com]. Here's the 10 images [spaceimaging.com].
  • Unfortunately, I think the stresses resulting from thermal contraction and crystallization would cause the shape to change.

    Also, you'd need very strong and rigid mountings to keep it from bending as you tilt it (mercury is heavy), so you're back to the same problem they're avoiding in the first place.

  • A staticly fixed telescope can have light sent to it by means of other mirrors but there are a few drawbacks:

    * The external mirror must be at least as large (and ideally larger) than the primaray telescope mirror, and be *flat* (to within a tiny fractions of a wavelength of light). Big *flat* mirrors are expen$ive.

    * The addition reflection(s) do more mirror reversals (not a big deal) and each reflection is a loss (this can be a big deal with faint objects).

    * The external mirrors need more structure as they have to be mounted someplace and have to be able to be moved and possibly track.

    If you were setting out to map all the sky, a fixed telescope would be a bad idea. But if you only need a rather random sample of sky -- which seems to be the case here -- a fixed telescope will do nicely. The choice is made by latitude. Need a different set of data? Build another system at a different latitude.
  • Good use of a Bloom County reference!

    I suggest +4 to your karma and a substantial research grant (enough to buy all the reprints of Bloom County and Outland)

    Always remember: Mars Needs Women

    Yeah, the hogging of all those cool scopes gets me down, but there are some very nice ones you probably don't know about. Check with local colleges and universities to see if they have one available to astronomy clubs. I know there's a pretty good one at Saginaw Valley State University, through which I could see moons of Jupiter. Too bad I live in California (state motto: Light Pollution? What light pollution?) now.


    --
    Chief Frog Inspector
  • If you're looking at any object in the sky
    (beside the celestial north pole, that is),
    it will leave a circular trace on a long-time
    photographic exposure. To counteract this
    effect, you let the telescope rotate in
    the opposite direction of the earth's rotation.
    Obviously, this isn't possible with the
    mercury telescope.
  • Wow, I could really use one of those...oh wait, I don't have $1 million. Hmm, I know, I'll take that barrel of surplus liquid mercury I found in that abandoned warehouse, pour some into a dinner plate, point it at the sun, and stare at it for hours on end! Ooops, I spilt some, oh well, I'll just use this washcloth to wipe it up...wow, this stuff sure is fun to play with....I wonder what would happen if I filled a clear trash bag with it, got inside, and went as the Terminator for Halloween!! I'll bet I'll get lots of candy that way! Hmm, maybe -I- could sell myself as a $1 telescope, point me in the right direction, and bam, you've got a view clearer than that of Hubble, for a fraction of the price!
  • 'Cause you've got pictures of the Olympics, and NBC has exclusive broadcasting rights...

  • Uhm... (Score:1)

    by Anonymous Coward
    Isn't the IOC going to sue them for offering their perspective on the Olympic Games?

    http://spaceflightnow.com/news/n0009/25ikonos/08 .html
  • I already posted something about this in a different thread, so I'm repeating myself I know, but: liquid, metallic mercury is not an enormous safety hazard. Mercury is dangerous chiefly in chemical combination (and organic compounds of mercury are the real killers), and metallic mercury is quite inert. The chief danger is in prolonged exposure to mercury vapor; liquid mercury is slightly volatile at room temperature.

    But...there's nothing else with mercury's properties. A eutectic alloy of gallium and indium (and possibly some other metal, I can't quite remember) is marketed as a kind of mercury substitute. Gallium melts somewhat above room temperature, but the gallium-indium eutectic melts lower. The difficulty is that, while mercury does not "wet" most surfaces, gallium does. Capillary action would distort the surface of a rotating gallium-indium mirror, especially if the layer of liquid were thin (to reduce weight and conserve the costly metals.)

    hyacinthus
  • I can understand it when the l337 posters to Slashdot don't actually read the articles, but I'm beginning to get peeved with how many times Hemos et al. apparently do not read the stories. Had Mr. co-inventor of the mercury telescope read the article, he would see that,

    "The concept of LMTs can be mapped back to the 18th century.... The concept was sound, but the technology available was too crude to make it work.... Following these experiments, LMTs were a curiosity in the history of physics until the early 1980s. "It was nearly a forgotten concept that had a bad reputation because past attempts were unsuccessful," said Borra."

    It was, no doubt, due to the technical innovations provided by Hemos and Bill Hall that curiosity was rekindled in the early 1980's.

    By the way, the equilibrium shape of liquid in a uniformly rotating container is parabolic. Not that it would matter if it were catenary or spherical (as most glass lenses are due to limitaitons of the grinding process) because these are all approximately paraboloidal in the paraxial approximation.

    Bingo Foo

    ---

  • Sirs (and madams),

    We need mirrors to those images! They're not slashdotted per-say, but they're very hard to take a look at without a broken image (max connections).

    Thank you.
  • Have you seen my web page?


    --
    Chief Frog Inspector
  • You don't have to rotate the whole thing...

  • This was actually talked about in Simpson case (Score:3)

    by Vassily Overveight ( 211619 ) on Tuesday September 26, 2000 @08:32AM (#752842)
    There were some people who wanted to find out if the NRO (National Reconaissance Office) had any photos of Nicole Brown's neighborhood at the time the murders were taking place. They wanted to see if OJ's car was there. I don't know if NRO even answered the request, but no photos were ever forthcoming.

    I suspect that with the new commercial services that don't have the classification issues, we'll be seeing satellite photos used routinely in both civil and criminal matters.

  • Umm, since when are mirrors responsible for exposures in the first place? That's a function of whatever imaging equipment you hook up to the telescope (i.e. camera) and not the mirror, or the telescope itself.

    Yeah, but to get a long exposure, the telescope has to track the object as the earth rotates, which means it has to be able to move.

    Also, normal telescopes don't "see anything outside their lattitude" either. Last time I checked, they don't move any more than mercury-based mirrors do. ;>

    Well, the building doesn't move, but the telescope can tilt up and down.

  • Yeah, UBC rocks... too bad they make us Computer Science majors learn fucking SCHEME!!!! Humbug.
    "God is dead." - Nietzsche

  • Re:Dangerous?? (Score:3)

    by technos ( 73414 ) on Tuesday September 26, 2000 @08:37AM (#752845) Homepage Journal
    Oh, come on! The health hazards of liquid mercury are not nearly as bad as you may have been led to believe! I would rather see children play with liquid mercury in science class once a week then spend time in classrooms sprayed with Dursban insecticide and disinfected with single-agent antimicrobials!
  • >At the same time, it does not speak well of the scientific community if it's members are adopting an attitude of, "This telescope is mine! Mine! Get your own!"

    I'm not really so sure that it's a matter of "owning a telescope" or "over-using it". There are thousands of astronomers and not that many telescopes. This is the case with most pure science research since it requires extremely expensive apparatus (telescopes, accelerators, detectors, etc). With everyone trying to explore different aspects of science it makes it harder to determine who should be allocated the most time with this equipment. The way it is right now, many people must plan a whole year around getting to use a certain device for a week.

    Once again it comes down to who's going to give out money for this research. Since particle physics/astrophysics/astronomy has little relevant technological usage (at our current levels of technology) there really isn't a reason for people to dole out the money for it. And that is why it seems like everyone is getting the shaft...

    I'd have to agree with you that the ego's are a very real part of it, but I think that's unavoidable. Obviously people who do make significant contributions to the furthering of their field will be given more opportunity to continue with their research. I guess it just comes down to a personal matter of whether or not they are persuing it for the personal gains or the joy of making new discoveries and advances in itself.

  • The problem is not one of sharing, it's that there are many things in the heavens to look at and not enough telescopes to go around. This problem is compounded by the fact that observing can only be done at certain times (night, when there is no moon, when the object you want to observe is visible, etc.).

    This problem can be helped somewhat by offloading some of the more mundane tasks to amateur astronomers. These include finding Earth-crossing asteroids and comets and making observations of variable stars. Think of it as distributed net for telescopes.
  • A slight difference of meaning here.

    A standard telescope can see pretty much anything visible from the latitude at which it is located, aside from problem of mount design (the 100 inch at Mt. Wilson can't see near 90 degrees N because the mount is in the way) or due to all the atmosphere and ground clutter within about 15 degrees of the horizon.

    A mercury telescope can't be pointed excpet straight up. As in it points to the zenith and not anywhere else, like a utility pole. The standard telescope can track against the earth's rotation; the mercury mirror telescope cannot.

    Since it can't point away from the zenith, no long exposures are possible. The exposures are limited by how long before the earth's rotation cuases blurring, or if there is tracking across the focal place, how far off-axis the tracking can occur. It may be possible to get a couple minutes, but nothing like the long exposures -- sometime measured in hours -- that can be had with a standard telescope.
  • I hope the IOC doesn't sue Ikonos. Thier satellite took a picture of the Olympic Games (incriminating evidence at http://spaceflightnow.com/news/n0009/25ikonos/08.h tml )
  • However, I wonder what their scenario is in case of a fire.

    Hold your breath.

    Run like hell.

    Hope no-one will notice.

  • Let me start by saying I found the pictures taken by Ikonos fascinating. Recent movies (Enemy of the State) and forthcoming software games ( Black and White [lionhead.co.uk]) have shown this capability to scale from a distant view of the earth from the moon all the way down to a view from an airplane fly-over. Amazing.

    I'm glad that the Ikonos people are displaying these images. However, I am somewhat alarmed at the potential misuses for such technology in a "commercial" environment. I suppose the commercial misuses can only be as bad as the governmental misuses that are no doubt already occuring. (Who really doubts that the < insert your favorite agency here > doesnt already have recon satellites with much greater resolution and advanced sensors?)

    How long should we continue to rely on crowd anonymity [google.com]? When will the people/corporations be accountable for their actions? Is the almighty dollar the only authority anymore?

    Am I being too paranoid/conspiratorial/etc? I dont know...

    But I do know that those pictures of War in Grozny, Chechnya [qoqaz.net] were absolutely devastating. When I can worry about formatting for a website while others are worrying about food and shelter for the night, I think anything is possible.

    What do you think?

    Peace.

  • Wouldn't this be a bit dangerous---seeing the properties of Mercury?

    According to the article this has been considered. An epoxy-lined pit has been dug, if anything bad happens the mercury is trapped, and someone goes and gets a mop.
  • Somehow, that link, and the links on that page, don't show show me anything

    turn on javascript and reload.

  • Not that it would matter if it were catenary or spherical (as most glass lenses are due to limitaitons [sic] of the grinding process)...

    In truth, most professional glass telescope mirrors are ground to aspherical surfaces on a regular basis. Grinding produces a spherical surface; polishing and figuring can produce any number of surfaces, even surfaces which aren't conic sections (e.g. the surface of a Schmidt corrector plate.)

  • Re:Trademark Infringement (Score:3)

    by hanway ( 28844 ) on Tuesday September 26, 2000 @08:52AM (#752855) Homepage
    TransAmerica's probably a walk in the park compared to the International Olympic(26USC0001) Committee. I suppose the picture of the Olympic(26USC1234) Stadium in Sydney probably violates some kind of exclusive broadcast rights. The next logical step will be the IOC's lawyers to "cease and desist" flying satellites over the Olympic(26USC9876) venue.

  • Re:The "pointing straight up" part... (Score:3)

    by Signal 11 ( 7608 ) on Tuesday September 26, 2000 @08:53AM (#752856)
    Any impurities in the refocusing mirrors would be duplicated in the result. The whole point of a liquid mirror is to kill the impurities.

    --

  • Sorry to sound like a fool. But what exactly does
    1 meter resolution mean?
  • How do they keep miniscule air currents from causing even the littlest ripple? The platform is spinning, which will cause some air turbulence.

    Quite simple really... mercury is very very heavy. It would take a lot of air to cause it to ripple, so if you can keep it in a relatively wind-free environment, you'll be fine. Vibrations during the rotation of the mercury would be a much greater concern, methinks.

    ----
    Dave
    MicrosoftME®? No, Microsoft YOU, buddy! - my boss
  • It would certainly do what you suggest, but do you really want to open up that can of worms?
    Consider the problems inherent in having any and all scenes of potential criminal activity under constand satellite surveillance.

    Do you want the EPA to know that you change your own oil in your driveway?
    Do you want your parents to be able to check that you are mowing the lawn while they're at work?
    Do you want Joe Schmoe Cracker to be able to peep while your wife sunbathes in the buff in your back yard?
    Do you want to drive a black Camry, just like everyone elses, in an effort to protect what little privacy you'd have left?
    Do you really want to star in a Japanese version of "Big Brother" or "The Truman Show", without even realizing it?

    We should not open a door unless we're prepared for what might come through it.

    The REAL jabber has the /. user id: 13196

  • But you need an Up, and Down! The parabolic curvature comes from the balancing of centrifugal and gravitational forces. One of these on the moon would be cool though! No air currents, earthquakes, railroads etc. to disturb the mercury.
  • Astronomers usually only point at stuff that is generally above them where the air density is thinner. As you move towards the horizon, the air density becomes more and more distorted because of atmospheric turbulence, and opaque from dusts, etc.

  • Hi-Rez press/media versions of pictures (Score:5)

    by Smack ( 977 ) on Tuesday September 26, 2000 @09:00AM (#752862) Homepage
    A little know secret of the Space Imageing site is that you can pretend you're the media and get MUCH better versions of the images.

    http://www.spaceimaging .co m/ikonos/anniversary/media.htm [spaceimaging.com]

    Like that pretty 1800x1800 Olympic stadium image? How about a 3090x4516 San Fran image? (watch out, it might crash Netscape)

    Just watch out if you don't have a nice pipe. Let's see if spaceimaging can handle it.
  • The mercury mirror is pretty old news. Scientific American had an article about them a couple of years ago. One thing that was proposed for the readership, though, was to use the same idea to make big mirrors for homebrew telecopes. You place a circular container on a turntable (the kind to get sound out of those flat, black vinyl things your parents have in the basement), fill it with a slow-curing epoxy/resin mix, cover it to prevent air currents from rippling the finish, and turn the turntable on. A few hours later, you've got a parabolic dish. Pour in enough additional epoxy/resin mix, formulated to be even slower curing, will improve the quality of the surface by making a thin top coat. Silver coat the surface (or have it done professionally) and you've got as big a primary reflector as you want. SciAm reported results that were as good or better than most home-use telescopes. Place the container off center and your focal point will be off center, too, if you want to get creative.

    For really big epoxy mirrors (a meter or so in diameter), I would imagine you would want to drill out some of the material from the backside, or it would get pretty heavy and cumbersome.
  • I wonder if you could build a "perfect", by spinning some other molten metal (steel, aluminum, tungsten), then flash freezing it. Would the parabolic surface remain? Then you could coat the surface with a rightly relefctive matierial a few atoms thick!
  • As an amature telescope maker, I heard about this stuff at least a few years back. These things are limited in what they can do. The mirror lab in Arizona rotates blanks inside huge kilns to get them to rough shape. I don't remember the numbers but even with some of the best dampening systems available they have surface roughness on the blanks that mean they have to be finished conventionally. Astronomical mirrors are geneally measered in fractions of a wave length of 5500 angstrom light. 1/20 a wave is considered good for amatures. Tilt your mercury a little and you lose that accuracy. Side note: they generally run a film of oil over the mercury for saftey reasons.
  • Cooling the metal will cause it to contract. Since it is impossible to cool the metal entirely uniformly, the result would be distorted as cooling metal will change the position of the metal that has already cooled.
  • If the telescope was on the north or south pole, that is correct... the camera would be the only thing you would need to rotate. At all other latitudes, correcting for the rotation of the earth would require moving the entire telescope on the same axis, which is not possible since it can only point straight up. This telescope would essentially limit you to a very short exposure time, while the object you are viewing is directly overhead.
  • Neat news!

    The pulp-age SF writer Raymond Z. Gallun wrote about a mercury-mirror'ed telescope in his 1930s-vintage story "Old Faithful." It was used by a dissident martian scientist to observe Earth.

    Gallun, who died about eight years back, recounts doing a lot of his work after shifts as a watchman at a factory that had a hemp-fueled furnace...

    Stefan

  • i remember 10 years ago i read article on it, there's even at University Laval, here in Québec, a mercury mirror with other substances that allow you to move the mirror for +/- 10 degree or something like that, so you're not on one latitude only.
    --
  • I just KNEW the FBI was spying on my skyclad pagan sabbats. May as well have a radio tag in my ear... Moooooo.....

    The Divine Creatrix in a Mortal Shell that stays Crunchy in Milk
  • ...doesn't mean that you can't aim the thing. Remember, the huge cost of the mirrors in large telescopes comes from the cost of shaping a parabolic mirror. Flat mirrors, on the other hand, are extremely easy to manufacture by comparison. It may seem like a fairly crude way of accomplishing the task, but there might be a comparative advantage to simply placing a large plate mirror over the mercury dish to effectively redirect what it's focusing on.
  • a long exposure might be posbible with a static telescope if you tracked the target with a computer thingy, which was able to artifically adjust for the movement of the object through the viewing angle of the telescope. OK, so the exposure would be limited - 4 minutes per degree of viewing angle. do I make sense?
  • Right - contain the mercury in a dish of some sort that is spun like a centrifuge... The faster the spin, the more concave the "mirror" becomes...
  • As you move towards the horizon, the air density becomes more and more distorted because of atmospheric turbulence, and opaque from dusts, etc.

    s/air density/visibility/
  • This was a topic in the series of books called "Amateur Telescope Making" published by Scientific American back in the '30s. The problems of old are;

    1. It is a "Zenith transit" instument; It can only look staight up without a sidereostat or similar device of flat mirrors that removes much of the economy of this method.

    2. Tiny disturbances make ripples larger than one-quarter wavelength of yellow light. This messes up the image a lot. Modern technology can finally solve this problem with feedback loop motion contols and etc.

    3. Mercury is expensive. So one needs a cavity that is very close to the final mirror surface such that only a film is required.

    4. Mercury is a hazmat and evaporates over time.

    It's nice to see this old dog hunting again, though. This isn't the first time and not likely to be the last time.
  • The stuff that is getting moderated up in this discussion shows that the moderators don't know a thing about telescope optics.

    When you go out at night, your iris opens up to a maximum of about 7mm. If our pupils were larger (like a cat's) we could see even better in the dark (dim objects appear brighter to cats than to humans). This introduces us to the principle that the larger the diameter of our light collector, the brighter dim objects appear. This is why a telescope with a 10" diameter objective (mirror or in case of refractors, FRONT LENS) will show you dim deep sky objects better than a 6" diameter telescope.

    All of that light does little good if it is not focused down into a disk of light that will fit into the observer's pupil (7mm or less). That is why mirrors must be spherical or parabolic. . .to focus all of that light into a small space. The trick of telescope design is how to bend the resulting focal point out of the way of the incoming light. (It does little good if the focal point is placed where you have to block the incoming light with your head!) In the case of the common Newtonian design, a smaller mirror is placed in the way to bend the light path 90 degrees out the SIDE of the tube, where the resulting image can be examined under magnification (using various focal length eyepieces). This smaller mirror is called a "secondary". It must be kept small, since it IS blocking a small percentage of the incoming light.

    In the case of the mercury mirror, it is flat in respects its orientation to the earth that it sits upon. But in order to achieve a focal point, the mirror SURFACE is not flat, it must be spherical or parabolic. This is achieved by spinning the platter of mercury. Like stirring a glass of tea, the center dips and the sides rise. Once a constant rate is maintained the focal length will not shift.

    The poster's idea CAN NOT WORK (reflect light from other angles into the mirror). In the case of a spherical mirror, the focal point is reflected straight back at the secondary, so how do you view it. In the case of a parabolic mirror, the resulting image would be distorted. To avoid this distortion the path would have to be directed (at some point by yet another mirror, straight down perpendicular to the mirror. Again this additional mirror will be blocking our view of the resulting focused image. IN EITHER CASE, we are losing the benefit of the large mirror, because we must use a smaller mirror to reflect onto it (if we used a large mirror, we must be blocking too large a percentage of our primary mirror.

    Curious George

  • I was just now thinking, as perhaps a "kickoff" to get others thinking:

    1. Ok, by rotating the mercury, a parabolic shape is created that can be used as a mirror (I have that SciAm article somewhere - nifty to do it with epoxy!), but it can only point "up" (at whatever latitude you are at).

    2. Now, imagine if you created "artificial" gravity via a centrifuge-like device, that whirled these spinning dishes of mercury around (and you thought a single dish might cause problems!) - multiple dishes, angled (via a gimbal arangement, so that the vector for "down" can rotate about a "roll" axis) around this whirly thing - speed the thing up to allow the dishes to point in, slow it down to allow them to point more "vertical".

    3. Use a computer to "select" which dish to use, which will be one in a certain position - the dishes could be "snapshot" selected as they come into position.

    What I am trying to explain is hard to explain - I hope a few people understand. I also wonder if there would be some kind of anomolies in the "mirror" due to the various force vectors at play (leading to distortion in the surface)...

    I support the EFF [eff.org] - do you?
  • Yeah fuckwit, they can design and build a mercury telescope for $1 mil but they aren't smart enough to know that mercury will hurt them. You 'mercury is toxic' idiots are getting on my nerves. Mercury is bad, but it isn't like it will kill you on sight. Get an education first.

    FW, yourself. Where in my post did I even suggest toxic?

    Besides the fact that the British Columbia example is at a safe over-the-border distance from tort-happy lawyers and environmental extremists (other than perhaps Greenpeace), mercury is a liquid, subject to contamination (dew, pollen, dust), heavy and therefore requires special handling. Not quite the same as a solid object.

    It's a neat trick, but sounds about as dicey as carrying a bowl of tomato soup over a white carpet. Pity, too, that it's only for looking straight up. This really seems like the long way around the barn to build a telescope.


    --
    Chief Frog Inspector
  • If you cool the metal very very very slowly (ie, 50 degrees celsius over 1 week) then yes, you can cool it uniformly. Unfortunately it also requires the room to be at the same temperature as the metal, and, as most metals oxidize (especially at high temperatures) you would need to have a room devoid of oxygen (and other corrosive gasses).

    Then you need to accoutn for the machinery which spins the molten metal, which will also be at this temperature... Very tricky indeed.

    Technically unfeasable, but possible. No where near the same cost point as a precision ground mirror.

    -Adam

    Is that a firewall on your connection, or are you just happy to see me?
  • It seems pretty obvious that you need a gravitational field below the spinning disk of mercury to get a good lens shape.

    Even so, can anyone think of a way this could be used to build cheaper telescopes in space? At least in Zero G you could point the thing wherever you wanted. Perhaps short duration (vibrationless :-) ) thrust to provide artificial gravity for long enough durations to observe what you wanted to look at, then corrective "reset" burns afterward? Have one sitting at the end of a very long counterbalanced rotating arm with a fast enough collection device to observe while it was rotating?
  • But some glass mirrors have been cast in a spinning mold, to get the glass nearer to the final desired shape. Doing this eliminates a great deal of grinding. And, when this came up in Scientific American a couple of years ago, the the guy who writes the "Amateur Scientist" article suggested spinning a cake pan on a record turntable and filling it with epoxy, then using the resulting curved slab as a blank for final grinding and mirroring.


    ...phil
  • Actually, we can get a close guess based solely on the laws of optics.

    Using the Hubble Space Telescope as an example.

    Assume that the size of the Hubble is the maximum diameter mirror that can be launched. (Maybe not exactly, but probably close enough for this example.)

    Undergraduate physics:

    Resolving power R (resolution) of a diffraction limited telescope: R = wavelength/(2*diameter telescope)

    This means for the HST (2.4 meter) and visual wavelenght (500nm) R = 500nm/4.8m = 1*10^(-7)

    Since the Hubble is in orbit h = 680km (380 miles) high, this means it can theoretically resolve: Detail = R * h = 0.07.

    Thus 7cm (3 inch) details. Not enuff for reading license plates, even if someone would hold it up to the sky so we dont have inclination effects. (1/2 feet).

    Then you have to factor in camera resolution and difficulties in aiming the satellite, plus atmosphereic effects (which get worse the further away from straight down you are). The end result probably cuts the effective resolution by a half or two-thirds -- 15 to 20 centimeters.


    ...phil

  • leCmdr must have fixed it, I'm going back down. *grin*
    --
  • Two thoughts to your response:

    1) Couldn't you use a similar epoxy resin covering used on the earth based mirror to cover the space mased mercury mirror? I assume it's helping evaporation as well as image stability on the earth based one.

    2) If the mercury mirror were in a vaccum, would the mercury still evaporate? I'm imagining this would operate in orbit and not from the shuttle or on the ISS.

    I like the attractive material idea, I hadn't really thought about how to grap onto the mercurty to get it spnning. Perhaps you could also use a magnetic field of some sort?

  • Architecture itself is a public domain artform. The property owner is not able to control the taking of images, nor of their use. All they can really do is to escort you from the property if they don't like you and your camera.

    When Pan Am sold its famous building in New York City (Manhattan), the new owners were not allowed to alter the "Pan Am" sign on the building, as it was deemed a historic landmark. People know the building as the Pan Am building, even though the company didn't quite reach the stellar fortunes as seen in Stanley Kubrick's 2001: A Space Odyssey.

  • I'd read about this mirror technique years ago, and it occurred to me that you could easily cast near-perfect parabolic mirrors by spinning molten aluminum in a shallow ceramic dish and letting it cool.

    You could keep the weight down by making the dish roughly follow the curve of the mirror (with grooves where you want ribs to be). You'd cast this in an argon atmosphere to keep the aluminum from burning (reacts with oxygen, carbon dioxide, and *maybe* nitrogen at those temperatures).

    The mirror would have an optically perfect finish when it set, and wouldn't corrode (aluminum oxide is impermeable to oxygen, so you get a one-molecule-thick oxide layer).

    Is there something I'm missing here, or would this indeed make a good way to produce medium-sized mirrors for hobby telescopes and larger segmented telescopes?

    (You can build a segmented telescope with identical mirrors; you just have to do processing to deconvolve the resulting blurry pixels. You know the point spread function, so this can be done losslessly. A group already built a cheap segmented telescope with spherical mirrors that does this.)
  • Yeah, substuting for Pritchet, no? Or was it Vandenberg's class?
  • i think you would end up defeating the purpose of using mercury to make bigger reflectors(and therefore collect more light) b/c the only time a primary reflector could be used is the tiny fraction of a second when it is pointed in the proper direction during its rotation on the gimbal(not the mercury dish's axis) and would therefore only be gathering a tiny amount of light per minute. even if you used many small mercury dishes i dont think it would work due to the extremely small time you could leave the aperature open because of the very small (arcseconds at most) area being viewed.

  • And the fumes make you go maaaaad."

    He's wrong. This has been researched extensively, and you would have to sit in the dome for the entire operational time to go maaaad.

  • Uh-oh, I posted about this on the UK Publishes Asteroid Armageddon Report [slashdot.org]-thread. And, since it seems awfully relevant to this article, I guess I'll just repost.... Wonder what happens to my karma...? Here we go:

    Well, building a largish dedicated telescope is one thing, but I would rather start researching a possibility that would be much more useful, namely building a network of Liquid Mirror Telescopes [ulg.ac.be]. A liquid mirror telescope has a mirror of mercury that is rotating, forming a near-perfect paraboloid as it rotates. Obviously, you can't tilt the telescope, so you can't track objects like conventional telescopes, and you can't look wherever you like, you can only look straight up. The field is also pretty small, but if you put a lot of LMTs on different longitudes and latitudes, you will be able to scan most of the sky. And since LMTs come at the prize of 1/100 of the cost of a similar size of a conventional telescope, you can build a lot of them. So, say we start mass manufacturing (several hundred) 8 meter LMTs and place them all over the place.

    This should be done by international agreements, and the data should be put in public domain. It would not only be useful in looking for NEOs, but all kinds of monitoring projects, e.g. Gravitional Lens monitoring (which is my research area), Gamma Ray Burst follow-ups, the list is long. Of course, short exposure times is a problem with LMTs too (90 secs), but that can be fixed by combining nights.

    There are substancial technical problems connected with a global network of LMTs, first, we don't know how the mercury will behave (turbulence in the atmosphere is a problem, now you might get turbulence in the mirror as well... :-) And, you won't see adaptive optics like you see on e.g. VLT on an LMT). Another problem is the huge amount of data produced, and how to treat it and give every potential user access to it. These are problems that must be overcome, but I believe that it should be possible to do, and definitively more worthwhile than building dedicated instruments for NEO search.

  • But with LMTs, the day of individual astronomers owning their own telescopes may have dawned.

    Come-on! How many amatuer astromoners own their own telescopes. [answer: most of them] I can spend $5,000 and get something that can do some interesting reserch, as long as I have the motorvation. Near earth asteroids, comets, (and with luck) nova, supernovas etc.etc. I hardly think that just because you need big $$$ that you can't contribute.

    (blatant ploy to moderators) It's just like open source, you don't need a multi gigaflop machine to write code, just the motorvation.

  • The only problem I can think of is that the aluminum oxide coating that naturally forms on any piece of aluminum may not be reflective enough to be used as a mirror.

    A good thought, but I doubt that this would be a concern. Firstly, the oxide layer is only one molecule thick (as previously mentioned), and so should be too thin to influence incident light.

    Secondly, there's already good empyrical proof that aluminum works - most telescope mirrors are made by vapour-depositing aluminum on glass.

    I'd been worrying about airborne dust scratching the mirror and dulling the finish after a while, but the fact that conventional optics already use it implies that this isn't a big problem.
  • This is rubbish. It may not work economically, but optically, the following setup works:

    At the top, a large (say 10m x 6m elliptical) optically flat mirror, mounted steerably. This reflects light from the chosen area of the sky, so that it comes straight down the barrel of the LMT.

    Next a small flat secondary mirror, say 1m x 50cm elliptical, suspended above the LMT, on its axis, just below the focal point, tilted permanently at 45degree. The back of this mirror, and it's mount need to be very black. This mirror moves the focal point of the LMT (where you want to put your cameras, etc.) off to one side, out of the way.

    Optically this works, and you replace the problem of steering a parabolic glass mirror, with the problem of steering a rather large optical flat. The latter problem is certainly easier (ie cheaper) but I'm not sure how much cheaper.

    Finally the LMT.
  • Mercury is toxic and it evaporates

    Keep the mirror in a vacuum / sealed chamber.

    A cool aspect of the design is that you can change the magnifying power of the telescope by spinning it faster or slower. Neat!

  • I'd say it's more like the differnce between a taxi and a bike if you're a delivery person. The Taxi's nice but it's shared between hundreds of people, so you only get it for short periods of time. A bicycle has a more limited range, but it is far cheaper so you can afford to use it all day, every day. You also have the option of sharing, as opposed to the need.

    The fact that the mirror only points straightup isn't that bad. As somoene else pointed out, you can move the target some for tracking, aiming, etc. You may not be able to track the whole sky, but you can build a lot with the $99MIL that you save (like building another 99 telescopes around the world that CAN point where the first one can't.

    It would also increase the viewing time by a factor of 100

  • I understand what you are saying - but I wasn't thinking this thing would be small - I was thinking that this device would actually be pretty huge (with dishes the size of the larger air-bearing mounted dishes). Still, you are right in saying that the amount of light that would be collected would be small (since this thing would work similarly to a motion picture camera, in a stop-motion time-domain kind of way) - this would limit its usefulness to real-time study at best, and time-lapse would be next to impossible, I would imagine.

    Let's say you sped up the rotation of the thing - let's say you could spin the sucker (man, and would it be a sight!) up to 2000 rpm - increasing the sampling rate - would this help? I know it would be dangerous, for certain - if it were even possible.

    IOW, there is a difference between a mirror that is always there in one position, vs one that is there for brief blips of time (with longer times in between where it is not there). But what if those brief blips happened so fast (due to higher speed and more spinning mirrors) that at any one point on the disk, if looked at steadily, the mirror was always "on" (just "flickering" rapidly)?

    Of course, I just thought of something that would mess up everything - Corriolis force/precession issues. If it didn't destroy the machine outright, it most certainly will cause problems with the mercury.

    NBD - it was all just a thought exercise anyhow. Thanks for replying!

    I support the EFF [eff.org] - do you?

Slashdot Top Deals

Algebraic symbols are used when you do not know what you are talking about. -- Philippe Schnoebelen

Close