I like that they used Glycerin as a protective layer for the mercury. Glycerin is notable for having the same Refractive index as Glass. So it's like a layer of liquid glass.
Modern telescope mirrors do not have to be frequently repolished. That went out in the late 1800’s with the invention of silver on glass mirrors. Instead, the glass is polished once, then coated with an extremely thin layer of reflective metal. The first metal used for the purpose was silver, which can be deposited by a very interesting chemical reaction from water based solutions. Starting in the 1930’s, vacuum evaporation of aluminum replaced chemical silvering and remains the most common method. Gold can also be done this way for improved infrared reflectivity a la Webb Space Telescope. Instead of repolishing an aluminized mirror, the aluminum layer is dissolved away chemically, then a new aluminum layer is deposited by the vacuum technique. This is routine at professional observatories. There are TH-cam videos of the process.
Wouldn’t chemically dissolving a coating and reapplying a new coating be considered repolishing so to speak? I get “polish” is the act of physically removing an oxide layer to expose a layer below, but I wouldn’t nitpick the process the way you have.
@@Wild_Bill57 In optics, polish means mechanically rubbing the surface to remove material on a very fine scale. You can’t repolish a precision optic without changing the shape of the surface on the same scale as the very fine adjustments that are necessary to make the optic perform acceptably. If you polish the surface, you have to redo a very tedious process of testing, polishing, and retesting until you get back to the precise shape needed. Chemically removing and then reapplying a metal coating without significantly changing the shape of the underlying glass surface is not considered repolishing. It is called recoating, a much less time consuming, much more predictable and straightforward process. The metal coatings are so thin that they reliably reproduce the precise surface shape of the underlying glass. Because glass is fairly chemically resistant, the metal coating can be removed without significantly changing the shape of the glass. Before the metal on glass technology was invented, telescope mirrors were made of a solid metal alloy. When the surface tarnished, it did have to be mechanically repolished, and that meant the whole, laborious, tedious fine adjustment process had to be redone. It was such a bother that for much of the 19th century, only lens, not mirror telescopes were constructed. (Lord Ross’s 6ft diameter telescope was an exception.) Lenses become impractical above about 1 meter diameter. In the early 20th century, George Hale pioneered larger mirror telescopes at the Mount Wilson Observatory using the silver on glass technology. These telescopes proved extremely effective for the new science of astrophysics and stopped development of large lens based telescopes. In the 1930’s, aluminum on glass replaced silver on glass.
Hi, I'm an astrophysicist working with the International Liquid Mirror Telescope (with Paul Hickson, actually). Super excited to see LMT's featured on SciShow!
Hi! Could you explain something that's always bothered me. (and Googling gets people like me saying "how come they don't?) It seems reasonably easy and cheap to make a flat mirror. So with a flat mirror, (or two) couldn't you look in any direction with a liquid mirror telescope? Thanks in advance.
@@gasdive A flat mirror doesn't focus light: it just sends it back in the direction it came from. A powerful telescope uses a curved mirror to focus light from a large area into a camera, allowing us to see very faint objects.
@@orbemsolis I meant a mirror that redirects light so that it goes vertically down into the curved liquid mirror. Imagine lying on your back, looking straight up. Hold a mirror at 45 degrees above you, and you'll be looking horizontally. You can see 360 degrees around you by rotating it around a vertical axis (while maintaining 45 degrees to the vertical). . Another mirror at 45 degrees that rotates around a horizontal axis in line with the view of the first mirror let's you look in any direction. It's hard to explain without waving my hands around.
We did a lab for a fluid mechanics class in grad school where we started with the Navier Stokes equations in cylindrical coordinates and derived a equation for the shape of a rotating body of water. We then set a pot of water on a pottery wheel to measure the actual shape and compare to the theory.
Large telescopes rarely use parabolic mirrors anymore. The most common design is some version of the Ritchey-Chretien that has two curved mirrors. The big one is concave and the second, smaller one is convex. Both are polished to hyperbolic, or something similar to hyperbolic, shapes. This compensates for aberrations inherent in the parabolic design for any subject that is not exactly on the telescope’s central axis (the center of the field of view). The R-C design was invented in the 1930’s and became common for large telescopes in the 1960’s. There are other, more complex designs now, too. Opticians have become increasingly sophisticated in their abilities to shape mirrors and lenses.
Iirc they did note that modern mirrors are usually made up of smaller shapes. I think there may have been a mix up while writing this episode. It sounds like they wrote about the original benefits of lmt's and didn't clearly separate then from more modern designs. I think the polishing thing you spoke of in your other comment (very interesting btw) may be a similar mistake. Where they started writing about the benefits of lmt's and forgot or intentionally omitted later improvements because in a way they weren't relevant to the story. The main point of this video seemed to be that some guy figured out a "crazy design" way back that countered contemporary limitations. Back then it didn't work out but now we're actually using it. Although this is just my guess 😄 I have no more knowledge than you. Also I found both your comments were interesting.
The two most common are Ritchey-Chretien and Gregorian (first-designed reflective system: primary parabolic and secondary concave elliptic). Magellan telescopes, GMT, LBT, VATT use Gregorian system
@@skz5k2 Thank you for that clarification. I did not realize there were that many large Gregorian telescopes in use. Do they use some form of hyperbolic curvature like the Ritchy-Chretien to minimize coma and astigmatism? As I recall from reading years ago, the classic Gregorian design has a lot of coma and/or astigmatism unless the f-ratio is very high.
I live near the UBC telescope. And the problem was as you said. The longest nights are in the middle of winter and you can some years get 2 or 3 clear weeks in January, you can't rely on that.
I’d imagine any minor imperfection would be magnified and spread throughout the resulting image, making it impossible to resolve via any form of correction.
You might consider doing a video on the spinning glass mirror casting oven at the University of Arizona. Mirrors up to 8.5 meter diameter have been cast this way. The physics of producing a parabolic curve is exactly the same as with liquid metal mirrors. In the spinning glass casting oven, the idea is to produce a glass mirror blank that is close to the final required curvature. Blanks cast this way still need grinding and polishing to produce a finished mirror, but the amount of glass that needs to be ground away is greatly reduced, enough to make the extra trouble of the spinning oven worthwhile. Roger Angel pioneered this technique. Oddly, the mirror lab where these large telescope mirrors are produced is under the stands at the University football stadium.
The location is kinda funny. Imagine if someone put top secret scientific instruments under the stands of a football stadium. No one would ever think to look down there 😏 Also I doubt this would be a Scishow space video, but it would make a really cool vlogbrothers video. Or Veritasium for that matter. Would love to see how that works.
The thought of a stadium being build right over something important/iconic in some way, rings a bell somewhere deep in my memory, but I can't seem to find it lmaoo, it's a little frustrating but maybe it'll pop up someday lol
@@animalpeeps I think Arizona Stadium was there first. Probably you are remembering the first nuclear reactor built by Erico Fermi’s team under the stands of the disused Amos Alonzo Stagg Field at the University of Chicago during WWII.
What I'm really curious about is the casting of off-axis curvatures, like on the outer mirrors of the GMT. The central mirror I imagine they could just spin to create its surface curvature. But I'm guessing the outer mirrors would need to be spun off-center to create a bias in the curvature toward one side...? Not sure how that would work.
@@manualdidact I know that they have, in addition to the spin casting technology, sophisticated, computer controlled grinding and polishing. I expect they are using that to get the off axis correction.
One thing that's worth mentioning is the ability to do this on other astronomical bodies as well! Since the most fragile element of a telescope is the big mirror, using liquid for this makes it "self healing" and thusly far more resistant. Getting a glass mirror to the moon would be tough, but landing the frame and system for a LMT? Much easier. Plus, there you don't have to worry about the coriolis effects, and can create beautifully large mirrors with zero atmospheric disturbance
@@BabyEater I don't think we're quite there yet with making our own gravity. In order to currently create comparable artificial forces you'd have to spin the craft, and that would create coriolis forces on the spinning liquid disk that would probably hamper the shape of the surface.
06:23 I am about to work on that LMT in Himalayas from next week. Soon I'll be one of the few guys who know how to operate worlds largest liquid mirror telescope.
I've heard this suggested for a telescope built on the lunar surface, since it gets around both the size constraints of rockets and the fragility of mirrors trying to ship one there.
@@xpkareem I think the angular speed for a given shape goes as the square root of the gravitational acceleration, so if the gravity is about 1/6 earth, the rotational speed would be about 0.4 of on Earth. So, not a gigantic difference, but significant.
Transporting liquid Mercury via rocket strikes me as risky. Instead I might suggest transporting it in the form of a safer Mercury compound like Mercury Selenide, and then separating the two on the Moon.
I used to live at UBC when the LMT was still in operation. From UBC they would shine a green LIDAR laser above it. (UBC was about 70km away). If I remember they were looking at sodium in the atmosphere.
One of my lecturers is Prof. Brad Gibson who wrote one of the sources linked in the description. He played a part in the creation of the telescope in canada and may or may not have acquired the mercury in a less than legal manner
An interesting characteristic of some segmented primary mirrors, such as the one where I work -- the surface is actually spherical rather than parabolic, so that the segments can be identical, each with the same curvature. A segment can be pulled from anywhere on the mirror and replaced with any other. We have a small number of spares and this is how we rotate them through the resurfacing process, a few segments per month.
I guess they use a specially shaped secondary, either a mirror or a lens or correction plate, that compensates for the aberration of using a spherical primary.
@@MattMcIrvin In our case we have a very large stack of four mirrors (our "wide field corrector", total approx 1800lbs) that receives the light from the primary and corrects for spherical aberration, and ultimately the focal "plane" is still a very shallow spherical surface. It's a metal plate, on which are mounted a large number of fiber bundle ends, each guiding the incoming light to a specific spectrograph instrument. Light from a particular target is positioned onto the bundle for the intended instrument. The optics are way outside of my expertise, but my understanding is that these corrector mirrors are roughly spherical, with varying degrees of 'aspheric departure'.
What about using gallium to transition between the perfect liquid parabola (by heating it up) and then letting it cool into shape as a solid perfect mirror. This will give you all the advantages of a liquid mirror but you avoid the problems of ripples and dust during operations. You also have the solid mirror capacity to lift and point the whole lense once it's solid
Because Gallium will not crystallize perfectly and can still be attacked by its sorroundings (aka air and temperature changes) so that it becomes unusable
Other advantages: gallium is cheaper than Mercury, far less toxic, and much less dense, meaning the mirror would be lighter and cheaper than a mercury LMT.
@@isaacthek that's already how large mirrors are made, just that they're made from glass and coated with a fine metallic layer. The metallic layer gets resurfaced (etched away and re-applied periodically). A gallium mirror would need repolishing and would not be as stable as glass.
I'm guessing an oxide layer could form on the solid metal over time, not sure of gallium's metallic nobility. Also, it's very likely that the liquid and solid density is different and the final shape would be bigger or smaller, like how ice expands. That being said, you could account for the shrinkage in your spinning "cast" form with enough computation.
Strictly speaking a parabolic mirror focuses light to a point only for rays parallel to the axis. Rays coming in at an angle exhibit comatic aberration. Requiring a coma corrector.
How about try to make a Liquid Mersenne-Cassegrain Telescope with mercury, glycerol and potassium? Just put the liquids in a recipient with a circular wall at the center and rotate. The mercury stays in the bottom with a parabolic shape and potassium (63.5°C) stays on top of the glycerol with a parabolic shape with different focus lenght because of the different densities of the materials and the gradient of the rotation with respect to the depth of the reflective surfaces. I had this idea with two telescopes, the liquid-mirror telescope and the monolithic telescope.
I was about to get all upset before I watched the video and say "Hey wtf I say one of those about 20 years ago when I was wondering around the woods." Turns out I was walking in the trails around THAT VERY liquid mercury telescope. It just happened to be a day they were starting to installing the first bits of mercury. Its about an hour from downtown Vancouver and at the time I just walked up and opened the door and said hello. The people inside were super nice and explained about the mercury mirror. 👍👍👍
While it is nice alliteration, it’s not “cloudy Canada”. UBC just happens to be cloudy because it is in a rainforest. It was probably one of the worst spots to build such a telescope.
The other issue is the fact that it can’t take long exposures, since the earth is rotating there is no easy way to keep it fixed on one spot in the night sky for extended exposures. The price to pay for a cheap large reflector.
You should look into photographic zenith tubes formally used by the naval time observatory. They used a pool of mercury as their mirror. No spin needed. The reason I was told by the designer was that it was always level.
A perfect candidate for a space telescope. Able to make compactly enough to fold into a nose cone and operates in an environment that's free of contamination. Also gets around the problem of undirectional use. I have been mulling over this concept for decades. Ever since I first heard about using mercury for a mirror. Multiple mirrors all facing inward to the centre of a rotating carousel which is giving them centrifical force to keep the mercury pinned to the back of the mirror as the mirror rotates. At the centre would be a series of other flat mirrors, (45° to the mercury) aimed at whatever it is you want to look at. The result would of course create a situation where it would appear that the thing you were attempting to view was always rotating. However, we now have the computer technology to make corrections for things like that.
I heard about an idea to do this, but on the moon and make it huge. It would have to be heated I guess, but it would be pretty powerful, telescope wise.
Slight mistake at 0:57 "Called a parabola which focuses all the light rays that come in at any angle onto a single point". If focuses all light rays that come in at a parallel angle onto a single point, otherwise the telescope would have no directionality.
2:08 The centre of the pool is NOT "pulled down by gravity". Rather it gets shallower as most of the mercury has been spun towards the perimeter of the mirror leaving less in the centre.
I live a stone’s throw away from that telescope. My girlfriend and I walk on the dikes in Maple Ridge to distress from a very stressful job.we we’re walking one day and saw a shiny thing right in the middle of the mountain. I wanted to know what it was. I looked it up and found out where it was. It was up at the UBC Research forest in Maple Ridge We went up there looking for it to go on an advenute😊 it wasn’t on any maps and I don’t think we were suppose to go up there. We hiked up and found d it. It was soooooo cool. They even had a big display of what it saw. I’m a bit of an astronomy nut so it made my summer.
The liquid metal shown in the stock footage at 20 seconds isn't mercury. Mercury beads so strongly you don't get that "globby/string-like" behavior as you pour it. It also wouldn't stick to the container like that. Makes me think it was gallium stock footage that somehow got mis-labeled as mercury.
Spinning liquid surface forms a hyperboloid (rotation of coshx curve about the zed axis), which requires a strong computer to transform. The coshx shape does not collect all collinear light rays without distortion, as a paraboloid would.
Cesium is liquid at body temps, solid when cooler. Perfect for night viewing. Wonder why they didn't use it... oh yeah, it explodes on contact with damp air.
The Richard F. Caris Mirror Laboratory at the University of Arizona Tucson spins an entire furnace to create a parabolic glass mirror. It is under the bleachers at the football stadium, and quite a thing to see when spinning. Huge!
It's neat to think I thought of something independently before seeing this video that was at one point thought of to be an important invention, ever since looking into my first dobsonian I wanted to try a liquid metal mirror
A liquid mirror can't be tilted away from the horizontal because the fluid would pour out, destroying the mirror. But that does not mean a liquid mirror telescope cannot be pointed. Optical designers are now experimenting with ways of electromechanically warping secondary mirrors suspended above a liquid mirror-or even slightly warping the liquid mirror itself-to aim at angles away from the vertical. Similar techniques are used to point the great Arecibo radio telescope in Puerto Rico.
If you could set this up on a barge or ship, that stabalized it's self against the movement of the waves, with gimbals, piezoelectrics, etc, you could move it up or down to different latitudes in order to point it at different stars, galaxies, etc
Mercury's toxic, gallium's too expensive... but Canada's at it again, apparently: "Recently Canadian researchers have proposed the substitution of magnetically deformable liquid mirrors composed of a suspension of iron and silver nanoparticles in ethylene glycol. In addition to low toxicity and relatively low cost, such a mirror would have the advantage of being easily and rapidly deformable using variations of magnetic field strength." en.wikipedia.org/wiki/Liquid-mirror_telescope
It would be amazing to develop a mirror material which could incorporate fluid dynamics to heal sections. Like a laser manipulator which could be placed on a space telescope to resurface damaged areas. We've seen how quickly micro impacts have been peppering the JWST so the bigger proposed successors would be even more vulnerable. Perhaps an inflatable self repairing impact shield could be placed to intercept debris along paths which wouldn't obscure the observations.
Is it possible to use gallium instead of mercury. Galllium has melting point around ambient temperature. One could heat it just enough to be liquid, spin it up to create the parabolic shape and cool it down to keep it. This kind of mirror can then be moved around without deforming.
The intro with the metal pouring out of the vial into the glove is not mercury, it’s probably gallium or a gallium alloy. It’s sticking to the plastic and it’s starting to solidify
One solution to the pointing thing would be to move the secondary mirror/imager around. They did this with the Arecibo telescope and it worked there. I don't know is the curvature needs to be a modified parabola for that though. Probably does. A big problem with this is that one of the forces is gravity and you can't move or adjust that. But if you were using some other metal besides mercury that is magnetic then you might have something that you can adjust with magnetic fields. Gravity would still be a huge factor but maybe some magnets could shift it around to point where you like.
Just a bit of armchair science-ing, are there other liquid metals that are magnetic? Was thinking of instead of physically spinning, maybe use magnets to manipulate the LM to shape in parabola and possibly tilt it?
Mercury is basically the only metal that is consistently liquid at room temperature and standard pressure--there are some others with really low melting points that aren't too far off. Maybe they could use some kind of metallic suspension...
Dumb question.. But could you make massive perfect mirrors "cheaply" by using a spinning Mercury mirror as a base, then preforming vapor deposition on it? (Tho tbh a UV sensitive epoxy/low melting point material might be better as it can be cured in place I guess, instead of draining the mirror risking damage/deformation)
I think for that to work you would have to "flash freeze" whatever material you used to make the mirror. If you didn't it would freeze in a shap you don't want.
If the problem is only pointing at the zenith, how about a flat mirror above the zenith scope that could be angled to track things not at the zenith? A big flat mirror would have to be easier to create than a big parabolic mirror.
Hmm...I wonder if this technology could be vastly improved by introducing that "T-1000" technology you talked about not too long ago. Have the magnets shape the mirror into a perfect parabola while it's warm, let it cool while it spins so it holds that shape, then once it's solid it can be tilted to look at a far wider section of the sky. Then when it needs to observe something much closer or farther, melt and reshape it again, rinse-repeat.
What if we could use a reflective membrane and a vacuum to control the curvature of the membrane that would be super cheap and possible to transport anywhere 🤔
*_Using many LMT's over a wide area all pointing straight up can collect more data..._* By combining images from many LMT's a larger data set is possible. While each LMT's can only collect a small vertical slice of sky, others will have their own slice. Since the Earth is a globe, it's curve can be used so each telescope is pointing at a different region of the night sky. Since LMT's are 1/10th the cost of glass mirror telescopes, using 10 would cover a larger portion of night sky. Imagine 100 spread over 10 miles, or 1,000 over 100 miles. *_No tracking is needed either. The sky moves and the LMT's remain stationary._*
@Cody'sLab If only there was a space nerd with access to a boatload of mercury who lived in a super remote area.... If anyone reading this knows how to send Cody the link to this video, it'd be appreciated! I'd love to see an amateur version of this!
I remember one of his mercury videos, you can see heat ripples in the air from mercury evaporating, he even mentions it... that scares the daylights out of me :(
Does anyone know where someone can recycle mercury? The kind that used to be used in wall thermostats that controlled central heat & air units in homes or businesses.
A parabola doesn't "focus all the light rays that come in at ANY ANGLE onto a single point" (1:00). If it really did so, it would be useless as a telescope or antenna reflector. Instead, light that travels parallel to the axis of symmetry of a parabola and strikes its concave side is reflected to its focus, regardless of where on the parabola the reflection occurs.
We should put a giant liquid mirror telescope at the South Pole, assuming the costs of heating it above the melting point of mercury and spinning it using energy available at the Amundsen-Scott station aren't a problem. This way, it could capture an unparalleled deep-field view of the sky at exactly 90 S without the Earth's rotation posing the same problem as with zenith telescopes at other latitudes.
What if we have a liquid material like molten glass or silver and spin it and let it cool down while it spins. Wouldn't that also work to create a perfect parabolic suffice?
An lmt would be idally situated on either the north or south pole so that the image would remain stationary.Theres no upper limit on the size of the reflector so assuming space is homogenous, we could see anything the Webb could see. Monatomic gold could be amalgamated into mercury increasing reflectivity in infrared.
We need to put one in a forever dark crater on the moon. It would be a giant spinning disk of mercury. It would probably need some kind of heating to stay liquid. It would be like Arecibo, but for optical and infrared light.
What's amazing is that nowadays, no one even needs a telescope to study space. You can just use Google Earth or videos on TH-cam to study. Next, we'll use virtualized space for astronomy and gastronomy, with the introduction of chorizostronomy. Telescopes are so last century.
The thing is... he could used a large flat mirror to look at other directions. Albeit it defeats some of the advantages, manufacturing a flat mirror is way easier than a parabolic one.
I wonder if it would be possible to make a space telescope kinda like this. Perhaps form a drop of liquid that is spinning as it grows. Perhaps it would be possible to make a massive lens of sorts?
Did anyone else watch the Dr. Paul Hickson interview about liquid mirror telescopes? I found it really interesting as it is something that can be achieved realistically in my lifetime.
The bigger the telescope the more important it is to be able to track the target as the earth rotates. Only something at the actual earth's axis would not need that. But it would need to rotate the camera with the sky still.
I always wondered why they don’t freeze the mercury so they can point the resulting mirror. Yeah condensation might be an issue but you could solve that by trapping dry air near the surface, perhaps under a glass panel.
Since its so cheap, I’d love to see an absolutely massive one or network of these being built. It seems like such bang for buck, so why not have hundreds of huge zenith telescopes strategically placed to capture large swathes of the night sky?
This is not a cost effective way to capture more of the sky. You pay 10% as much on the lens, but the sky coverage is only a tiny fraction of a percent of the coverage of a solid mirror telescope. For some research, you can find something useful anywhere in the sky, and that's where these are useful. So you just need enough of these to meet demand. No need to focus on coverage.
Such an instrument may only aim at zenith : Because of it's weight, you can only maintain a perfect parabolic shape on a strictly horizontal plan. The more you magnify the image, the more you magnify earth's rotation speed: At 600x magnification, you have your aim in the field during less than 10s. Therefore, a big liquid mirror telescope, which you can not point where you want, is practically almost useless...
I always find it sad when someone dies without seeing the amazing things that come from their work. Seems like he would be pretty proud of his idea if he knew that it turned out we were using it in the age of JWST.
"Less than one tenth the cost". Outstanding!!
You just made my day by not saying, "More than ten times less".
Agreed! Phrases like that drive me nuts, and I speak math pretty good.
@@clarencegreen3071 *pretty well
I've developed a phobia of division as so much hardware cannot do it right, I now only want to multiply by fractions.
I like that they used Glycerin as a protective layer for the mercury. Glycerin is notable for having the same Refractive index as Glass. So it's like a layer of liquid glass.
Glycerin is also much sweeter than mercury!
Yeah but what about chromatic aberration?
@@Scrogan Fix it in post processing.
@@Derekzparty Glycerin is also much sweeter than glass
it probably also reduces the amount of mercury molecules that can gas off the mirror . so safer.
Modern telescope mirrors do not have to be frequently repolished. That went out in the late 1800’s with the invention of silver on glass mirrors. Instead, the glass is polished once, then coated with an extremely thin layer of reflective metal. The first metal used for the purpose was silver, which can be deposited by a very interesting chemical reaction from water based solutions. Starting in the 1930’s, vacuum evaporation of aluminum replaced chemical silvering and remains the most common method. Gold can also be done this way for improved infrared reflectivity a la Webb Space Telescope. Instead of repolishing an aluminized mirror, the aluminum layer is dissolved away chemically, then a new aluminum layer is deposited by the vacuum technique. This is routine at professional observatories. There are TH-cam videos of the process.
Thank You❣️
👏🏼😌
Wow, thank you for the lesson! I mean that sincerely.
I'm learnding!
Wouldn’t chemically dissolving a coating and reapplying a new coating be considered repolishing so to speak? I get “polish” is the act of physically removing an oxide layer to expose a layer below, but I wouldn’t nitpick the process the way you have.
@@Wild_Bill57 In optics, polish means mechanically rubbing the surface to remove material on a very fine scale. You can’t repolish a precision optic without changing the shape of the surface on the same scale as the very fine adjustments that are necessary to make the optic perform acceptably. If you polish the surface, you have to redo a very tedious process of testing, polishing, and retesting until you get back to the precise shape needed.
Chemically removing and then reapplying a metal coating without significantly changing the shape of the underlying glass surface is not considered repolishing. It is called recoating, a much less time consuming, much more predictable and straightforward process. The metal coatings are so thin that they reliably reproduce the precise surface shape of the underlying glass. Because glass is fairly chemically resistant, the metal coating can be removed without significantly changing the shape of the glass.
Before the metal on glass technology was invented, telescope mirrors were made of a solid metal alloy. When the surface tarnished, it did have to be mechanically repolished, and that meant the whole, laborious, tedious fine adjustment process had to be redone. It was such a bother that for much of the 19th century, only lens, not mirror telescopes were constructed. (Lord Ross’s 6ft diameter telescope was an exception.) Lenses become impractical above about 1 meter diameter. In the early 20th century, George Hale pioneered larger mirror telescopes at the Mount Wilson Observatory using the silver on glass technology. These telescopes proved extremely effective for the new science of astrophysics and stopped development of large lens based telescopes. In the 1930’s, aluminum on glass replaced silver on glass.
Hi, I'm an astrophysicist working with the International Liquid Mirror Telescope (with Paul Hickson, actually). Super excited to see LMT's featured on SciShow!
Are you from UBC? I'm from ARIES, also working on ILMT
@@kumarpranshu2533 Yes I am!
Hi!
Could you explain something that's always bothered me. (and Googling gets people like me saying "how come they don't?)
It seems reasonably easy and cheap to make a flat mirror.
So with a flat mirror, (or two) couldn't you look in any direction with a liquid mirror telescope?
Thanks in advance.
@@gasdive A flat mirror doesn't focus light: it just sends it back in the direction it came from. A powerful telescope uses a curved mirror to focus light from a large area into a camera, allowing us to see very faint objects.
@@orbemsolis I meant a mirror that redirects light so that it goes vertically down into the curved liquid mirror.
Imagine lying on your back, looking straight up. Hold a mirror at 45 degrees above you, and you'll be looking horizontally. You can see 360 degrees around you by rotating it around a vertical axis (while maintaining 45 degrees to the vertical). .
Another mirror at 45 degrees that rotates around a horizontal axis in line with the view of the first mirror let's you look in any direction.
It's hard to explain without waving my hands around.
We did a lab for a fluid mechanics class in grad school where we started with the Navier Stokes equations in cylindrical coordinates and derived a equation for the shape of a rotating body of water. We then set a pot of water on a pottery wheel to measure the actual shape and compare to the theory.
Large telescopes rarely use parabolic mirrors anymore. The most common design is some version of the Ritchey-Chretien that has two curved mirrors. The big one is concave and the second, smaller one is convex. Both are polished to hyperbolic, or something similar to hyperbolic, shapes. This compensates for aberrations inherent in the parabolic design for any subject that is not exactly on the telescope’s central axis (the center of the field of view). The R-C design was invented in the 1930’s and became common for large telescopes in the 1960’s. There are other, more complex designs now, too. Opticians have become increasingly sophisticated in their abilities to shape mirrors and lenses.
Thank You❣️
..here too😁
I think you should start a TH-cam channel.
Iirc they did note that modern mirrors are usually made up of smaller shapes. I think there may have been a mix up while writing this episode. It sounds like they wrote about the original benefits of lmt's and didn't clearly separate then from more modern designs.
I think the polishing thing you spoke of in your other comment (very interesting btw) may be a similar mistake. Where they started writing about the benefits of lmt's and forgot or intentionally omitted later improvements because in a way they weren't relevant to the story.
The main point of this video seemed to be that some guy figured out a "crazy design" way back that countered contemporary limitations. Back then it didn't work out but now we're actually using it.
Although this is just my guess 😄 I have no more knowledge than you. Also I found both your comments were interesting.
The two most common are Ritchey-Chretien and Gregorian (first-designed reflective system: primary parabolic and secondary concave elliptic).
Magellan telescopes, GMT, LBT, VATT use Gregorian system
@@skz5k2 Thank you for that clarification. I did not realize there were that many large Gregorian telescopes in use. Do they use some form of hyperbolic curvature like the Ritchy-Chretien to minimize coma and astigmatism? As I recall from reading years ago, the classic Gregorian design has a lot of coma and/or astigmatism unless the f-ratio is very high.
Stuff like this is the “hold my beer” of science and engineering
I live near the UBC telescope. And the problem was as you said. The longest nights are in the middle of winter and you can some years get 2 or 3 clear weeks in January, you can't rely on that.
Considering all the places in Canada with longer nights and less clouds (and less night pollution)!
@@katherinegilks3880 And colder temperatures...
Makes sense. I remember an old piece of laser testing equipment that used a pool of mercury as a self leveling reflector as part of its setup
There were some ground vibration detectors made from those as well that was used to detect tunneling escape attempts.
Another big problem that you didn't mention is the mirrors and lenses get so big that they deform under their own weight
Which is the whole idea with Liquid Mirror Telescopes! Turn a problem into an opportunity.
Guess what makes liquid telescopes work, lol
Would it be worth spinning a solid mirror just to use physics to help it retain its shape?
I’d imagine any minor imperfection would be magnified and spread throughout the resulting image, making it impossible to resolve via any form of correction.
That's why many large modern telescopes use segmented mirrors instead of one big monolithic mirror.
You might consider doing a video on the spinning glass mirror casting oven at the University of Arizona. Mirrors up to 8.5 meter diameter have been cast this way. The physics of producing a parabolic curve is exactly the same as with liquid metal mirrors. In the spinning glass casting oven, the idea is to produce a glass mirror blank that is close to the final required curvature. Blanks cast this way still need grinding and polishing to produce a finished mirror, but the amount of glass that needs to be ground away is greatly reduced, enough to make the extra trouble of the spinning oven worthwhile. Roger Angel pioneered this technique. Oddly, the mirror lab where these large telescope mirrors are produced is under the stands at the University football stadium.
The location is kinda funny. Imagine if someone put top secret scientific instruments under the stands of a football stadium. No one would ever think to look down there 😏
Also I doubt this would be a Scishow space video, but it would make a really cool vlogbrothers video. Or Veritasium for that matter. Would love to see how that works.
The thought of a stadium being build right over something important/iconic in some way, rings a bell somewhere deep in my memory, but I can't seem to find it lmaoo, it's a little frustrating but maybe it'll pop up someday lol
@@animalpeeps I think Arizona Stadium was there first.
Probably you are remembering the first nuclear reactor built by Erico Fermi’s team under the stands of the disused Amos Alonzo Stagg Field at the University of Chicago during WWII.
What I'm really curious about is the casting of off-axis curvatures, like on the outer mirrors of the GMT. The central mirror I imagine they could just spin to create its surface curvature. But I'm guessing the outer mirrors would need to be spun off-center to create a bias in the curvature toward one side...? Not sure how that would work.
@@manualdidact I know that they have, in addition to the spin casting technology, sophisticated, computer controlled grinding and polishing. I expect they are using that to get the off axis correction.
why not take a sheet of mylar , stretch it over "large pot" , create a bit of vacuum inside the pot and presto, you get a very large concave mirror .
but spherical rather than parabolic.
Also it doesn't have that good reflective quality.ok for mere school projects
One thing that's worth mentioning is the ability to do this on other astronomical bodies as well! Since the most fragile element of a telescope is the big mirror, using liquid for this makes it "self healing" and thusly far more resistant. Getting a glass mirror to the moon would be tough, but landing the frame and system for a LMT? Much easier. Plus, there you don't have to worry about the coriolis effects, and can create beautifully large mirrors with zero atmospheric disturbance
Or put it in space and make our own "gravity" and point it wherever we want
@@BabyEater I don't think we're quite there yet with making our own gravity. In order to currently create comparable artificial forces you'd have to spin the craft, and that would create coriolis forces on the spinning liquid disk that would probably hamper the shape of the surface.
06:23 I am about to work on that LMT in Himalayas from next week. Soon I'll be one of the few guys who know how to operate worlds largest liquid mirror telescope.
I've heard this suggested for a telescope built on the lunar surface, since it gets around both the size constraints of rockets and the fragility of mirrors trying to ship one there.
What is the math on that with the reduced gravity? I assume it would have to spin much slower than it would on earth.
@@xpkareem I think the angular speed for a given shape goes as the square root of the gravitational acceleration, so if the gravity is about 1/6 earth, the rotational speed would be about 0.4 of on Earth. So, not a gigantic difference, but significant.
Transporting liquid Mercury via rocket strikes me as risky. Instead I might suggest transporting it in the form of a safer Mercury compound like Mercury Selenide, and then separating the two on the Moon.
I used to live at UBC when the LMT was still in operation. From UBC they would shine a green LIDAR laser above it. (UBC was about 70km away).
If I remember they were looking at sodium in the atmosphere.
One of my lecturers is Prof. Brad Gibson who wrote one of the sources linked in the description. He played a part in the creation of the telescope in canada and may or may not have acquired the mercury in a less than legal manner
Wow I got that the secret is the spin almost immediately at the beginning of the video. I felt so intelligent 🥳❤️
An interesting characteristic of some segmented primary mirrors, such as the one where I work -- the surface is actually spherical rather than parabolic, so that the segments can be identical, each with the same curvature. A segment can be pulled from anywhere on the mirror and replaced with any other. We have a small number of spares and this is how we rotate them through the resurfacing process, a few segments per month.
I guess they use a specially shaped secondary, either a mirror or a lens or correction plate, that compensates for the aberration of using a spherical primary.
@@MattMcIrvin In our case we have a very large stack of four mirrors (our "wide field corrector", total approx 1800lbs) that receives the light from the primary and corrects for spherical aberration, and ultimately the focal "plane" is still a very shallow spherical surface. It's a metal plate, on which are mounted a large number of fiber bundle ends, each guiding the incoming light to a specific spectrograph instrument. Light from a particular target is positioned onto the bundle for the intended instrument.
The optics are way outside of my expertise, but my understanding is that these corrector mirrors are roughly spherical, with varying degrees of 'aspheric departure'.
Hey, I am an astrophysicist working on the ILMT with Dr Paul Hickson. Hoping to get data very soon! Very Excited!
What about using gallium to transition between the perfect liquid parabola (by heating it up) and then letting it cool into shape as a solid perfect mirror. This will give you all the advantages of a liquid mirror but you avoid the problems of ripples and dust during operations. You also have the solid mirror capacity to lift and point the whole lense once it's solid
Because Gallium will not crystallize perfectly and can still be attacked by its sorroundings (aka air and temperature changes) so that it becomes unusable
Other advantages: gallium is cheaper than Mercury, far less toxic, and much less dense, meaning the mirror would be lighter and cheaper than a mercury LMT.
@@antares8826 we could still use the same methodology of a second clear coat on top to protect it during formation and use?
@@isaacthek that's already how large mirrors are made, just that they're made from glass and coated with a fine metallic layer. The metallic layer gets resurfaced (etched away and re-applied periodically). A gallium mirror would need repolishing and would not be as stable as glass.
I'm guessing an oxide layer could form on the solid metal over time, not sure of gallium's metallic nobility. Also, it's very likely that the liquid and solid density is different and the final shape would be bigger or smaller, like how ice expands. That being said, you could account for the shrinkage in your spinning "cast" form with enough computation.
What a lovely ending phrase :)
Strictly speaking a parabolic mirror focuses light to a point only for rays parallel to the axis. Rays coming in at an angle exhibit comatic aberration. Requiring a coma corrector.
How about try to make a Liquid Mersenne-Cassegrain Telescope with mercury, glycerol and potassium? Just put the liquids in a recipient with a circular wall at the center and rotate. The mercury stays in the bottom with a parabolic shape and potassium (63.5°C) stays on top of the glycerol with a parabolic shape with different focus lenght because of the different densities of the materials and the gradient of the rotation with respect to the depth of the reflective surfaces. I had this idea with two telescopes, the liquid-mirror telescope and the monolithic telescope.
Surprisingly good pronunciation of Dunedin. American tourists here often seen to have entertaining amounts of trouble with it.
I was about to get all upset before I watched the video and say "Hey wtf I say one of those about 20 years ago when I was wondering around the woods." Turns out I was walking in the trails around THAT VERY liquid mercury telescope. It just happened to be a day they were starting to installing the first bits of mercury. Its about an hour from downtown Vancouver and at the time I just walked up and opened the door and said hello. The people inside were super nice and explained about the mercury mirror. 👍👍👍
While it is nice alliteration, it’s not “cloudy Canada”. UBC just happens to be cloudy because it is in a rainforest. It was probably one of the worst spots to build such a telescope.
Mirror mirror on the wal- OH GOD WHY IS THE MIRROR ALL OVER THE FLOOR?!
Watch the Movie.
(Snow white and the Huntsman series)
You must have a crystal ball.
Good for you Robert.
You are amazing!!! You are doing super good. Lots of Gratitude❤
The other issue is the fact that it can’t take long exposures, since the earth is rotating there is no easy way to keep it fixed on one spot in the night sky for extended exposures. The price to pay for a cheap large reflector.
You should look into photographic zenith tubes formally used by the naval time observatory. They used a pool of mercury as their mirror. No spin needed. The reason I was told by the designer was that it was always level.
Very nice of you to mention the Man from Dunedin New Zealand.
A perfect candidate for a space telescope. Able to make compactly enough to fold into a nose cone and operates in an environment that's free of contamination.
Also gets around the problem of undirectional use.
I have been mulling over this concept for decades. Ever since I first heard about using mercury for a mirror. Multiple mirrors all facing inward to the centre of a rotating carousel which is giving them centrifical force to keep the mercury pinned to the back of the mirror as the mirror rotates. At the centre would be a series of other flat mirrors, (45° to the mercury) aimed at whatever it is you want to look at.
The result would of course create a situation where it would appear that the thing you were attempting to view was always rotating. However, we now have the computer technology to make corrections for things like that.
10/10 closing pun
I love that something that sounds like the crazed invention of a madman is actually really useful.
Neat stuff, thanks for sharing.
00:12 Uhh, that clip was anxiety inducing at first, but turned out to be warmed up gallium in the end ;-)
You have to admire it for the time period and technology of that time it was an accomplishment and thanks for putting the two together..
woah I guessed why they would send liquid to space, and I was right
Spinning liquids curve lol
I heard about an idea to do this, but on the moon and make it huge. It would have to be heated I guess, but it would be pretty powerful, telescope wise.
Why not use gallium instead of mercury? Gallium liquefies as slightly higher than room temperature, and is non-toxic.
Slight mistake at 0:57 "Called a parabola which focuses all the light rays that come in at any angle onto a single point".
If focuses all light rays that come in at a parallel angle onto a single point, otherwise the telescope would have no directionality.
2:08 The centre of the pool is NOT "pulled down by gravity". Rather it gets shallower as most of the mercury has been spun towards the perimeter of the mirror leaving less in the centre.
Some say it's not the destination but the liquid telescope you met along the way
The "parabola" cross section at around the 2:16 mark loos suspiciously like an ellipse!
thank you for showing the first light image.
I live a stone’s throw away from that telescope. My girlfriend and I walk on the dikes in Maple Ridge to distress from a very stressful job.we we’re walking one day and saw a shiny thing right in the middle of the mountain. I wanted to know what it was. I looked it up and found out where it was. It was up at the UBC Research forest in Maple Ridge
We went up there looking for it to go on an advenute😊 it wasn’t on any maps and I don’t think we were suppose to go up there. We hiked up and found d it. It was soooooo cool. They even had a big display of what it saw. I’m a bit of an astronomy nut so it made my summer.
The liquid metal shown in the stock footage at 20 seconds isn't mercury. Mercury beads so strongly you don't get that "globby/string-like" behavior as you pour it. It also wouldn't stick to the container like that. Makes me think it was gallium stock footage that somehow got mis-labeled as mercury.
That was fantastic! Thank you!
Spinning liquid surface forms a hyperboloid (rotation of coshx curve about the zed axis), which requires a strong computer to transform. The coshx shape does not collect all collinear light rays without distortion, as a paraboloid would.
Cesium is liquid at body temps, solid when cooler. Perfect for night viewing. Wonder why they didn't use it... oh yeah, it explodes on contact with damp air.
The Richard F. Caris Mirror Laboratory at the University of Arizona Tucson spins an entire furnace to create a parabolic glass mirror. It is under the bleachers at the football stadium, and quite a thing to see when spinning. Huge!
It's neat to think I thought of something independently before seeing this video that was at one point thought of to be an important invention, ever since looking into my first dobsonian I wanted to try a liquid metal mirror
A liquid mirror can't be tilted away from the horizontal because the fluid would pour out, destroying the mirror. But that does not mean a liquid mirror telescope cannot be pointed. Optical designers are now experimenting with ways of electromechanically warping secondary mirrors suspended above a liquid mirror-or even slightly warping the liquid mirror itself-to aim at angles away from the vertical. Similar techniques are used to point the great Arecibo radio telescope in Puerto Rico.
If you could set this up on a barge or ship, that stabalized it's self against the movement of the waves, with gimbals, piezoelectrics, etc, you could move it up or down to different latitudes in order to point it at different stars, galaxies, etc
Mercury's toxic, gallium's too expensive... but Canada's at it again, apparently:
"Recently Canadian researchers have proposed the substitution of magnetically deformable liquid mirrors composed of a suspension of iron and silver nanoparticles in ethylene glycol. In addition to low toxicity and relatively low cost, such a mirror would have the advantage of being easily and rapidly deformable using variations of magnetic field strength."
en.wikipedia.org/wiki/Liquid-mirror_telescope
0:23 What is that thing hanging from the mercury bottle at the end?
Probably gallium starting to freeze. You don’t see any label on the bottle, so it might be gallium.
It would be amazing to develop a mirror material which could incorporate fluid dynamics to heal sections. Like a laser manipulator which could be placed on a space telescope to resurface damaged areas. We've seen how quickly micro impacts have been peppering the JWST so the bigger proposed successors would be even more vulnerable. Perhaps an inflatable self repairing impact shield could be placed to intercept debris along paths which wouldn't obscure the observations.
Is it possible to use gallium instead of mercury.
Galllium has melting point around ambient temperature. One could heat it just enough to be liquid, spin it up to create the parabolic shape and cool it down to keep it. This kind of mirror can then be moved around without deforming.
The intro with the metal pouring out of the vial into the glove is not mercury, it’s probably gallium or a gallium alloy. It’s sticking to the plastic and it’s starting to solidify
I'm glad someone else saw that
I work with the guy in the picture at the LMT. Still got the data too.
One solution to the pointing thing would be to move the secondary mirror/imager around. They did this with the Arecibo telescope and it worked there. I don't know is the curvature needs to be a modified parabola for that though. Probably does. A big problem with this is that one of the forces is gravity and you can't move or adjust that. But if you were using some other metal besides mercury that is magnetic then you might have something that you can adjust with magnetic fields. Gravity would still be a huge factor but maybe some magnets could shift it around to point where you like.
I used to make parabolic mirrors by rotating liquid resin while it hardened.
Just a bit of armchair science-ing, are there other liquid metals that are magnetic? Was thinking of instead of physically spinning, maybe use magnets to manipulate the LM to shape in parabola and possibly tilt it?
Mercury is basically the only metal that is consistently liquid at room temperature and standard pressure--there are some others with really low melting points that aren't too far off. Maybe they could use some kind of metallic suspension...
Lol, I'm old enough to remember when Zenith was a brand of TV📺😹
Do you remember what was originally significant about Zenith products though?
with an acoustic, no batteries needed, remote control. Just the basics: on/off, volume up/down, channel up/down.
Zenith: "The quality goes in before the name goes on."
@@clarencegreen3071 Thanks!📺
I also remember when TV repair shops existed!
Dumb question.. But could you make massive perfect mirrors "cheaply" by using a spinning Mercury mirror as a base, then preforming vapor deposition on it?
(Tho tbh a UV sensitive epoxy/low melting point material might be better as it can be cured in place I guess, instead of draining the mirror risking damage/deformation)
I think for that to work you would have to "flash freeze" whatever material you used to make the mirror. If you didn't it would freeze in a shap you don't want.
Such a simple and genius idea
If the problem is only pointing at the zenith, how about a flat mirror above the zenith scope that could be angled to track things not at the zenith?
A big flat mirror would have to be easier to create than a big parabolic mirror.
Hmm...I wonder if this technology could be vastly improved by introducing that "T-1000" technology you talked about not too long ago. Have the magnets shape the mirror into a perfect parabola while it's warm, let it cool while it spins so it holds that shape, then once it's solid it can be tilted to look at a far wider section of the sky. Then when it needs to observe something much closer or farther, melt and reshape it again, rinse-repeat.
What if we could use a reflective membrane and a vacuum to control the curvature of the membrane that would be super cheap and possible to transport anywhere 🤔
I thought the same thing. And if that is viable, it should also work in space.
*_Using many LMT's over a wide area all pointing straight up can collect more data..._*
By combining images from many LMT's a larger data set is possible. While each LMT's can only collect a small vertical slice of sky, others will have their own slice. Since the Earth is a globe, it's curve can be used so each telescope is pointing at a different region of the night sky.
Since LMT's are 1/10th the cost of glass mirror telescopes, using 10 would cover a larger portion of night sky. Imagine 100 spread over 10 miles, or 1,000 over 100 miles.
*_No tracking is needed either. The sky moves and the LMT's remain stationary._*
I remember the LMT at ubc in the mountains. Too bad west coast weather didn't help.
@Cody'sLab If only there was a space nerd with access to a boatload of mercury who lived in a super remote area....
If anyone reading this knows how to send Cody the link to this video, it'd be appreciated! I'd love to see an amateur version of this!
I remember one of his mercury videos, you can see heat ripples in the air from mercury evaporating, he even mentions it... that scares the daylights out of me :(
@@LordPhobos6502 Ooof! Liquid mercury all day, mercury vapor never! :O
> If anyone reading this knows how to send Cody the link to this video
you could tweet it at him
Cody: Hold my Mercury
@@PureAsbestos I know that's the obvious option but I'm not on Twitter :/
you could put the mercury pool in something like the spinning fair rides, that may solve the aiming issue
Does anyone know where someone can recycle mercury? The kind that used to be used in wall thermostats that controlled central heat & air units in homes or businesses.
A parabola doesn't "focus all the light rays that come in at ANY ANGLE onto a single point" (1:00). If it really did so, it would be useless as a telescope or antenna reflector. Instead, light that travels parallel to the axis of symmetry of a parabola and strikes its concave side is reflected to its focus, regardless of where on the parabola the reflection occurs.
We should put a giant liquid mirror telescope at the South Pole, assuming the costs of heating it above the melting point of mercury and spinning it using energy available at the Amundsen-Scott station aren't a problem. This way, it could capture an unparalleled deep-field view of the sky at exactly 90 S without the Earth's rotation posing the same problem as with zenith telescopes at other latitudes.
What if we have a liquid material like molten glass or silver and spin it and let it cool down while it spins. Wouldn't that also work to create a perfect parabolic suffice?
It'd still need post processing and polishing, but you would have less to grind off to get your mirror
An lmt would be idally situated on either the north or south pole so that the image would remain stationary.Theres no upper limit on the size of the reflector so assuming space is homogenous, we could see anything the Webb could see. Monatomic gold could be amalgamated into mercury increasing reflectivity in infrared.
We need to put one in a forever dark crater on the moon. It would be a giant spinning disk of mercury. It would probably need some kind of heating to stay liquid. It would be like Arecibo, but for optical and infrared light.
That liquid metal that is shown at ~0:15 being poured onto a pink glove does not like mercury. It looks more like gallium.
What's amazing is that nowadays, no one even needs a telescope to study space. You can just use Google Earth or videos on TH-cam to study. Next, we'll use virtualized space for astronomy and gastronomy, with the introduction of chorizostronomy. Telescopes are so last century.
The thing is... he could used a large flat mirror to look at other directions.
Albeit it defeats some of the advantages, manufacturing a flat mirror is way easier than a parabolic one.
Finally, someone used the word "toxic" in the proper context.
gallium? I assume denser Hg makes better reflection, but maybe it could cut some safety cost
I wonder if it would be possible to make a space telescope kinda like this. Perhaps form a drop of liquid that is spinning as it grows. Perhaps it would be possible to make a massive lens of sorts?
I suppose you could place this telescope at the north or south pole where the image would only rotate not pan.
Did anyone else watch the Dr. Paul Hickson interview about liquid mirror telescopes? I found it really interesting as it is something that can be achieved realistically in my lifetime.
The bigger the telescope the more important it is to be able to track the target as the earth rotates. Only something at the actual earth's axis would not need that. But it would need to rotate the camera with the sky still.
I always wondered why they don’t freeze the mercury so they can point the resulting mirror. Yeah condensation might be an issue but you could solve that by trapping dry air near the surface, perhaps under a glass panel.
When a liquid metal freezes it gets smaller and crystalises, this means that it isn't the same shape as the liquid it was before
I've heard an idea of filling a crater on the dark side of the moon with a film of mercury to make the mirror.
Since its so cheap, I’d love to see an absolutely massive one or network of these being built. It seems like such bang for buck, so why not have hundreds of huge zenith telescopes strategically placed to capture large swathes of the night sky?
Probably because while they would be cheap to produce, the toxicity would make them expensive to maintain.
This is not a cost effective way to capture more of the sky. You pay 10% as much on the lens, but the sky coverage is only a tiny fraction of a percent of the coverage of a solid mirror telescope.
For some research, you can find something useful anywhere in the sky, and that's where these are useful. So you just need enough of these to meet demand. No need to focus on coverage.
Such an instrument may only aim at zenith : Because of it's weight, you can only maintain a perfect parabolic shape on a strictly horizontal plan.
The more you magnify the image, the more you magnify earth's rotation speed: At 600x magnification, you have your aim in the field during less than 10s.
Therefore, a big liquid mirror telescope, which you can not point where you want, is practically almost useless...
you can use this effect to make glass mirrors too. you just spin molten glass, and keep it spinning until it cools.
I think that is actually part of the process for making large telescope mirrors.
@@danieljensen2626 isn't that what I just said?
@@katelights, no. What you said is "you can", not "they do".
The major inconvenient of a liquid mercury telescope is that it can only be pointed at the zenith.
Space liquid telescope can be oriented in any direction
Makes me ask what other "old" ideas we should revisit with current technology.
Building pyramids?
I always find it sad when someone dies without seeing the amazing things that come from their work. Seems like he would be pretty proud of his idea if he knew that it turned out we were using it in the age of JWST.
Brilliant