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Dirt Cheap Telescopes With Liquid Mercury
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 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!
"Can of worms? The can is open... the worms are everywhere."
...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 to more info about the telescope. Enjoy!
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.
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....
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
-Julius X
remove "-whatkindofspamdoyoutakemefor-" from email to send
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.
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?
Freedom: "I won't!"
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.
-Erf C.
Cthulu always calls collect...
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."
If the lameness filter actually worked, would you even be reading this?
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?
The next Cmdr Taco duplicate will be ready soon, but subscribers can beat the rush and see it early!
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?
What? Not a topdown look at Natalie Portman? Perverts!
--
Chief Frog Inspector
A feeling of having made the same mistake before: Deja Foobar
"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
"Tension is the great integrity" -- R. Buckminster Fuller
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.
Technoli
The HIPAS 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...
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?
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. ;>
Take a look at these:
Is it just me, or does picture number 1 look like a screen shot from SimCity? =)
What about picture number 6 then, looks like a screen shot from a scifi movie :-)
No "civilan targets" were destroyed... yeah right compare the pics before and after the war in Chechenya
09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0
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. Here's the 10 images.
"If I have seen further than other men, it is by stepping on their glasses." - Michael Swaine
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!
"Mmmm, coffee, life, programming, synonomous."
'Cause you've got pictures of the Olympics, and NBC has exclusive broadcasting rights...
It may look like I'm doing nothing, but I'm actively waiting for my problems to go away.
--Scott Adams
Isn't the IOC going to sue them for offering their perspective on the Olympic Games?
8 .html
http://spaceflightnow.com/news/n0009/25ikonos/0
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
---
taken! (by Davidleeroth) Thanks 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.
All browsers' default homepage should read: Don't Panic...
Have you seen my web page?
--
Chief Frog Inspector
A feeling of having made the same mistake before: Deja Foobar
You don't have to rotate the whole thing...
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.
"If I have seen further than other men, it is by stepping on their glasses." - Michael Swaine
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.
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 don't subscribe to RMS's GNUtopian vision.
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 )
Karma: SELECT `karma` FROM `users` WHERE `userid`=138474;
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 ) 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 ? 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 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.
peace
Sorry to sound like a fool. But what exactly does
1 meter resolution mean?
Java Web Application Development http://www.thinkobject.co
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
The REAL jabber has the user id: 13196
What you do today will cost you a day of your life
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.
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.
.co m/ikonos/anniversary/media.htm
http://www.spaceimaging
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.
The man who does not read good books has no advantage over the man who cannot read them. - Mark Twain
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.
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.
--
"Science will win because it works." - Stephen Hawking
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
The House Between - Original Sci-Fi Series
...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.
WARNING: there is a trojan on your
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...
But it certainly isn't a new idea. I saw a mercury telescope (IIRC, it was 10 feet) almost 5 years ago at HIPAS, a research facility near here (the vicinity of Fairbanks, AK) my friend's dad worked at at the time.
learn some html.....
Idea 1:
If someone (US govt, or corporations) got together about $50 million, we could put a bunch of these telescopes in various places on Earth and have the images digitally (they're using CCDs right?) stitched together to make a full panorama of the entire Earth's sky (not only showing the whole sky at once, but showing it in real time)!!!
Idea 2:
In space (orbit), there's no vibrations that could shake the mercury are there? Why not make a Hubble companion with one of these mirrors??? As I understand it, the biggest problem with making the hubble was building its main mirror.
-------
Oh shit! I forgot to click "Post Anonymously"...
IIRC University of Arizona, years ago, used spinning cooling ovens to pre-shape mirror blanks to a roughly parabolic profile. It drastically reduced the amount of grinding which had to be done, and thus the cost of the mirror.
--
Build a man a fire, and he's warm for a day.
Time is Nature's way of keeping everything from happening at once... the bitch.
--
Build a man a fire, and he's warm for a day.
Time is Nature's way of keeping everything from happening at once... the bitch.
The pictures from the story link were way smaller ant took forever to load. Your link had huge pictures that loaded in less than a second.
If I was a moderator I would rate this post +6 inspired from above. Pun intendid.
Thanks.
meept!
meept!
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.
Dog is my co-pilot.
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
***General Consultant to the Human Race*** My opinions are free. You get what you pay for.
--
Build a man a fire, and he's warm for a day.
Time is Nature's way of keeping everything from happening at once... the bitch.
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 - do you?
Reason is the Path to God - Anon
Mercury is a very well-known toxic substance which is easily converted to vapor and inhaled at room temperature.
Give me a nice, safe x-ray emitting CRT for my computational astrophysics any day...
Bob
Science, like Nature, must also be tamed, with a view turned towards its preservation.
It seems pretty obvious that you need a gravitational field below the spinning disk of mercury to get a good lens shape.
:-) ) 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?
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
"There is more worth loving than we have strength to love." - Brian Jay Stanley
Clearly, this is a problem for a mirror that we cannot move from a direction perpendicular to the ground. This problem would be greatest for mercury telescopes closer to the equator and least for mercury telescopes sitting nearer the true north or south poles. The TRACKING problem would be nonexistent at true north or south, but the object would still be ROTATING which would smudge details, as well.
Curious George
***General Consultant to the Human Race*** My opinions are free. You get what you pay for.
Not any more. Seems to be busted.
Anyone make a mirror of that site, by chance? I guess we've been locked out of it...
; -- the corruption of government starts with its secrets. a truly free people keep no secrets. --
leCmdr must have fixed it, I'm going back down. *grin*
--
Various known problems with mercury lenses:
1. After it's spun up, you have to wait a couple of days for the ripples to subside.
2. Mirror has to be in an effectively sealed room (yes, the fumes are bad, but proper ventilation and general avoidance can prevent health problems)
3. You can't perform adjustments on the surface to adapt for the atmosphere. This is what makes all of the current really large telescopes useful
You can aim one of these suckers by moving the secondary mirror and catching a different area of the reflected light. Kinda like holding a magnifying glass in place and moving your head around behind it. Since they're focused at infinity, the distance to the target is meaningless. Even a regular telecope only has so many degrees of valuable viewing, this is just a bit tighter.
Mythological Beast
Wake up - the future is arriving faster than you think.
The US Naval Observatory has been using mercury mirror transit telescopes for decades. They use them to determin whether or not a leap second has to be added. They take four exposures of a star on the same plate rotating the camera through 90 degrees each time. Depending on how skewed the quadrilateral the four images define is, they decide whether to add a leap second. I don't know exactly how long they have been using the techniques but they certainly had a Mercury mirror transit telescope back in 1986 when I toured the place.
Now I've seen it all!
Appended to the end of comments I post? 120 chars?!
The flat mirror you are thinking about would undo the cheapness of our $1,000,000 mecury mirror. The whole point is to avoid having to make a big mirror! While it might be a little easier to make a flat mirror that you are thinking of than it is to make a traditional parabolic one, it can't be that much cheaper. Think about making a 6m (3 x taller than me) optically flat thing that stays perfectly rigid while being pointed around. It's a nice idea, but a regular parabolic mirror would be better for your money because it would not cause another reflective loss like the pool of mecury would.
I can see it now, instead of "mad hatters" we'll be talking about "mad astronomers."
OH MY GOD! They're looking at me right now! AHHHHHHHHHHH! AHHHHHHHHHHH! AHHHHHHH! Raise middle finger to sky, feel beter. I'm ok now, back to homework.
Nope, it's still there. It was just a temporary hiccup.
Free Hans!
The best thing would be to build some 200 of these telescopes spaced a half-degree latitude or so apart. A scientist interested in a particular object would schedule time on the desired telescope for the time it would pass under that object. The telescopes should, of course, be all tied together via Internet2 so that as desired objects pass over a particular telescope a scientist's experiment automatically moves to that telescope. Though there would still be scheduling of experiments, at least up to 200 experiments could be concurrently scheduled on this beastie.
I don't see how the telescope's operation would be degraded by having a transparent cover on the whole device.
-- perl -e'print pack"H*","6e656d6f406d38792e6f7267"'
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.)
BFD
-Christian
our written thoughts are gifts to our future selves
I don't know who first had the idea, but Robert W. Wood at Johns Hopkins developed mercury mirrors to a pretty high state about 100 years ago. There is a well known portrait photo of him with his face also showing in the mirror. It used to be in one of my textbooks.
Wood is also known for exposing the N-Ray delusion. X-, alpha, and beta radiation had just been discovered and a French physicist went hunting for French radiation. With a noisy experiment and a hopeful heart he found it, of course. Wood visited the lab. With sleight of hand he removed and replaced a "crucial" bit of the apparatus -- all without affecting the events the guy thought he observed.
Sorta like cold fusion, huh?
Zax
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These images are great! Does anyone know where there are images of the entire earth in nice high res??? The only one's I've found online where quite bad (blurry, blocky or down right crap).
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IANAWhatever, but to get over the smearing factor caused by the rotation of the earth in long exposures, couldn't you just compensate for the rotation of the earth by:
1) Making it a digital LMT? (must find sensitive enough digital camera/film material though...that'd probably be a problem)
2) Somehow move the film past the aperature at such a speed as it would compensate for the earth's rotation? Think of this...multiple night full sky spanning! Have this film on some sort of conveyor long enough to scroll all night, then repeat with the same film the next night. Hubble himself did this when he tracked certain galaxies all night for multiple nights for 30 hour exposures, why couldn't we do the same type of thing? If we created enough of these things on different latitudes you could have a pretty good whole sky map in a few nights, depending upon the size of the field of vision of these things and cost etc...
Just a thought...
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King of the World
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Also, there are many types of work, e.g. surveys, where there's no need to have a scope that can point everywhere in the sky.
Yes, it's true you can't stay fixed on one point in the sky due to the earth's rotation, but that's ok. You just time-slice the data and add the frames back together with an offset between each successive slice. Something like this has to be done when you want to do photography with a Dobsonian. You're just counting photons. You need to know where each photon came from, that's all.
Re the schemes for letting the mirror freeze to make a solid mirror, this totally doesn't work, because the freezing and cooling process introduces gigantic changes in shape (gigantic, that is, compared to a wavelength of light). Even if it did work, the expense of a big scope is mainly the road to the mountaintop and the mount, not the mirror itself.
Ripples on the mercury are an issue, as suggested by a previous post, but they can be damped down with various techniques.
Yes, mercury is heavy, but you can make it very shallow by shaping the tub so it conforms very closely to the desired shape of the mirror. The only real limit is that if it gets too shallow (maybe 1 cm or 1 mm), surface tension effects start to affect the shape of the mirror adversely.
As far as using a flat mirror for aiming, this can be done. I think one version is called a Coude focus. However, the flat mirror has to be _big_ (as big as the curved mirror), so you don't necessarily get any advantage in terms of avoiding the giant mount. Also, you're usually using the flat mirror at an oblique angle, which wastes a whole bunch of its aperture.
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Don't you love when that happens?
jeb.
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. 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.
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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.
I remember reading about this in a New Scientist
article a while back. I've looked it up:
The abstract is
'Severe technical problems killed the liquid mirror telescope early this century. Now mercury mirrors are back - and they're hunting for space junk'
From New Scientist magazine, vol 147 issue 1986, 15/07/1995, page 38
An interesting article if you've got a load
of back issues lying around or a subscription
so that you can search the online archive.
(Free reg possible too)
Gee, an old idea surfaced again, just on a bigger scale. If the posters would hold back their self ego-centrism and dig up in a local library they will find out that an AMERICAN physisist (since /. seems to be obsessed with americans most of the time) Robert Wood created such a telescope back in 1930s and was using it quite successfuly for some time. Look for an ancient book 'Modern Wizard' by William Seabrook in antique book stores. It is rather strange to see the history repeat itself so precisely.
I thought of glueing blocks or a frame to reduce the amount of epoxy required to make the final shape. Without actually having made one, I think the problems with flexing and stressing that you referred to would be a problem. If you go ahead and use a bunch of epoxy, then you can remove enough solidified material after the fact to reduce the weight, but leave enough to prevent the mirror from losing it's shape. The epoxy itself is its own reinforcing structure, integral with the reflective surface. It means discarding a fair amount of hardened epoxy. Ideally, you wouldn't use it in the first place, but at least you maintain the quality of your reflecting surface during casting. Having the mirror be a solid block of epoxy makes it easy to drill mounting holes for a frame to orient it, too.
I had actually thought of making several large off-center parabolic mirrors with this method, coating them so as to get a diffuse focal point and orienting them to overlap the focal points. Total reflective area would approximatly equal a much larger mirror, allowing you to create a pretty powerful solar furnace. The diffuse focal point system works nicely for solar heating applications.
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Liquid can't be sustained in a vacuum. It will boil away. Liquid is a phenomenon of pressured environments.
The mercury could be frozen. Then the telescope could point anywhere.
I wonder if spinning mercury mirrors could form a good basis for searching for earth-orbit crossing asteroids. It would mean building a telescope at every few degrees of latitude and using the Earth's rotation for scanning.
The price of the optics could be right but the data-management task would be huge. It would also mean finding countries where the military would not get too bent-out-of-shape with people doing whole-sky scans -- I expect that rules out the USA.
I have seen fairly small mercury mirror systems (aperture of about 1 meter) and the technology is within the range of gifted hobbyists. Perhaps volunteer groups around the world could make such a system with some expert help.