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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.)
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."
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
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
"Tension is the great integrity" -- R. Buckminster Fuller
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...
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
Bruce
I am the real Bruce Perens.
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?
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
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.
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.
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
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.
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.
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.
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
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.
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
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
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
...phil
"For a list of the ways which technology has failed to improve our quality of life, press 3."
leCmdr must have fixed it, I'm going back down. *grin*
--
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.)
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.
Employee of Inrupt, Project Release Manager and Community Manager for Solid
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.