Why are telescope mirror & mirror blank so expensive ?👍

Glass: "Am liquid" Gallium: "Yeah, but yur too thicc" Glass: **sigh** "I feel invisible sometimes" Gallium: "Need a hug?" Mercury: "Ew. Get a room." And that, children, is why gallium coats glass and mercury is toxic.

Also, formula on 3:28 is wrong!!! Always, check your intuition. I know, you just c/p from wikipedia, but it is also wrong there. Much more intuitive is this: *Correspondingly, the dimensions of a symmetrical paraboloidal dish are related by the equation: 4FD=R^2 (therefore F=R^2/(4D)), where F is the focal length, D is the depth of the dish (measured along the axis of symmetry from the vertex to the plane of the rim), and R is the radius of the dish from the center.* BTW, I really like your channel!!!

Can you freeze the Galium while spinning for a fixed mirror in frozen state ?

This is how the 'star wars' satellite mirrors worked.

Yeah, I wish I could have been there when they made the GMT mirrors.... When I was i Tucson in 1999, I missed out on the Magellan II mirror....

I was about to ask why they don't just rotate a hot liquid metal/glass until it cools and hardens to make large mirrors, but I guess they actually do, cool!

Genius idea. Though that makes me wonder, they probably need the glass to be uniform thickness, so while they're spinning the thing to shape it, they need a mould under it which is equally perfect... How do they make that? Same process but with a different material?

Cool

@@redryder3721 Nah, they just need it to be close enough because they compensate for thermal expansion by making it a little bit thicker that way they won't have to make a perfect parabolic mold.

.

.

.

.

.

Never seen a scientist with man ban, what the hell? Am I still alive?

Cooll that you remember that. I also read about them many years back. I was always wondering if they where ever used.

If only we could use that technology in glasses...

What happens if the spinning is done in free fall? There is no force of gravity in free fall.

With sun light you can start a fire

@@davidmudry5622 then there is no parabola, and after a long time eventually surface tension dominantes, forming a somewhat round blob.

It’s a great channel that’s for sure

I think he can be pretty complicated, but I’m in yr 9. Despite this, I do agree that his content is interesting and informative

When I was in grade 6, I spent my whole day as a kid watching these kinds of videos but I haven't watched content creators like him, backyardscientist, etc.

Well they have to be interested in science first. I mean who doesn't like science? Star Trek is the best.

"Bill, Bill... " Always knew I would be educated while the teacher had the moment off. Definitely suggest ActionLab to my sister for educational purposes for her children.

Here is something useful and important to know 👉 The Connections (2021) [short documentary] 🔥

oh thats nice , din think bout that

Will it though? Other matter is competing to get to the edge.

@@JasonMitchellofcompsci I don't know for sure, but since there is no flow going on, just stationary liquid, the force alone would *probably* make any dust that's floating on the surface to slowly float away to the edge. At least that's my hypothesis :)

Dust being lighter than liquid metal would tend to collect in the center and not the edge. Oxides would move outward if they are denser than the base metal.

I wonder if it would work in zero-g...

Nothing, just stick the rotating bucket on the side of a rotating circular turntable.

@@VikingTeddy gravity is why the liquid doesn't fly away. It's still a mirror if it's sloshing around in the air, but not a very useful one. Liquid metal in space would tend to form wobbly globules...like the thick stuff inside a lava lamp, but reflective. As for the ideas to put the turntable on a turntable, you get uneven surfaces due to compound rotation, blurry (smeared) images of the moving target, or both. Photo exposures are fast OR crisp. It's very hard to get both. This is part of why movie footage and slow-motion is so heavily edited. Trying to do astronomy or see anything scientifically useful with this setup while inside a centrifuge would be a very expensive way to get blurry, streaked images. Cool effects...maybe? James says they _have_ to be pointed straight up...because they really do.

still do it ......with gallium.

This comment had no business making me as sad as it did.

Feel the irony. They'll sell it, make products, CFL bulbs and stuff ending in waste. It was probably safer with you.

Quitter! ;-)

Most likely the expansion / shrinking of the material will not make this work. Unless you take that in account somehow by adjusting the speed

I don't think the surface is gonna freeze and remain shiny.

thats sounds like too complicated, just use electricity to give it a shape

What if the liquid was made in layers, each one made separately? This would prevent the imperfection of expansion and shrinking. Also, you could make the layers and cover it afterwards, so the surface would always remain shiny, even when the base material isn't suitable.

Rather than freezing a spinning liquid metal, we might as well use a concave mirror made out of a metal like Stainless Steel, which I guess would technically be a frozen liquid metal 😂

Imma smoke Rightttt at the end 🤣🤣

🗿🗿

Share to the left…..

Puff... What?

Noice

Same here. Badly in need of a friend who has interest in physics, biology, geology, history etc. etc. that I have interest in. 😔

Not as good as the sides and the middle experiences different amount of stretching making the edges wavy. But depending on your quality needs you might find that if you oversize the dish the middle part might be good enough / large enough for your needs. Then you just mask out the bad parts.

Ah true, that could also be a factor along with what he said.

That's interesting !

My assumption are that it will shrink as it cools down thus making it loose its paraboluc shape

Also it mas shrink uniformly so the para bolic shape will be retained

Here is something useful and important to know 👉 The Connections (2021) [short documentary] 🔥

Interesting thought. Can we mix the gallium or mercury with epoxy and spin it to the desired focus as it hardens?

Someone else here mentioned that that's actually a technique used in parabolic mirror production!

I tought the same thing.

Yeah for a low cost diy mirror you can probably use wax and then use electrolysis to nickel-chrome coat it. I wonder how well it would compare to a bought mirror. But you can control the temperature fairly well with an inexpensive heater in a closed room, bring the room to 40-45C and then pour the molten wax, then just let the room cool down naturally so convection is a non issue.

The problem with metal mirrors is that they don't last very long. You quickly get tarnishing of the surface and trying to polish it off will ruin the optical finish. Glass mirrors also tarnish, but they can be easily washed and recoated without causing damage.

@@markh.876 What if the gallium floats over the resin as it may be heavier because it's a metal, leaving just a shiny coat at the surface of contact between the resin and the gallium after the curing of the resin🤔🤔

@@markh.876 Or just spraying any reflective coat to the parabolic shape cured resin which was left cured while rotating with the same method

@@markh.876 that’s why ppl use phase conjugate mirrors. So the outbound distortion cancels the in bound.

There are lenses made out spun epoxy that hardens while spinning that are thin metalized.

At that point, just spin the liquid glass. I'm pretty sure parabolic mirror manufacturers already do that.

For Newtonians which are not too small, it is usually the equatorial mount (I don't like Dobsonians).

There is something like: Gallium Liquid Mirrors

Have you experienced mercury poisoning?

@@kriptomavi presumably the mercury was not internal, which is where it's poisonous. Check out Cody's Lab for some great mercury experiments (like floating an anvil...yes, iron floats) and debunking some of the phobia. He is very careful with it in order to keep from contaminating his property, but touching with unbroken external skin for short periods is not generally dangerous. Breathing, eating and contact with cuts or abrasions would be a potential problem.

It was still smart to come up with the idea on your own. One time when I was trying to understand horsepower I got to the point where I thought “wait, doesn’t that mean that a horsepower measurement has to be at a specific RPM?” I was super excited to find out that I was right, because it meant I understood the physics enough to come to a correct conclusion. Not exactly advanced physics but I was pretty proud of myself haha.

I have came up with quite a few ideas but found out that others have done those way before. Like falling water display showing time etc, derived equations for time dilation and length contraction from specific relatives two postulates, laser oscilloscope, spin moulding some rings from polythene bags in a cotton candy spinner, electrolytic heavy isotope enrichment, And quite a few others. Btw i don't feel happy to find out that others have beaten me to the punch

Exactly. He wrote the mathematical relationship correctly at the end, but said it the wrong way around several times.

Here is something useful and important to know 👉 The Connections (2021) [short documentary] 🔥

Hmm. Wouldn't 20x stronger tidal forces on the surface of the moon warp the lenses too much? and the sticky dust...

@@CanalTremocos I'm pretty sure tidal forces on the moon from the earth can be ignored since there's only 1 side facing earth all the time. Also for dust...there are materials which are impermeable to solid matter but allow light through them.

@@CanalTremocos or it sounds like you're confusing tidal forces with gravity, one maybe caused by the other but only gravity gets stronger the closer you are. The tidal forces stays the same unless the object actually increases in mass.

..Lots of people here. .are talking about using the mylar space blanket to form a parabola...But how to hold that shape permanently?

wont be good for optical applications but will be good for other light focusing applications - more expensive, involved, and time-consuming, than alternative methods (like mylar pulled into shape by a vacuum)

What about using the mylar as a - ve mold for resin bu pushing insted of pulling it?

Pour some UV sensitive resin on top of the spinning gallium and then hit the resin with UV for around 10-20 seconds until cured. The cheap $20 curing lights on amazon will work for curing, and they have the 3d printer resins.

What they actually do is just spin a furnace holding a glass blank up to the speed needed to make the parabola they want, then cool it down slowly to avoid flaws, before grinding any imperfections and then buffing it to reflect. And that's a gross oversimplification of how to make a telescope mirror.

It's really complicated , first , same concept of lens telescope applies , the weight of such a large prism would weigh down the shape and ruin the magnified image as it will be out of focus , second, the earth's atmosphere makes images kinda distorted no matter how accurate your mirrors are , for this reason , the mirror telescopes mirror is set on top of servos that can slightly flex the mirror to compensate for it. Check out the new series of extremely large ground telescopes using mirrors ,

how does such a telescope look like? Maybe they use both, the big one to focus the light, then prisms to redirect it?

Maybe it’s because the light need to get into the prism to have a total reflection and get out of it. Since we can’t ensure that light will always be perpendicular to the surface of the prism, the process of getting in and out will separate light into different colors.

Why don't they just use a plastic reflecting surface

Here is something useful and important to know 👉 The Connections (2021) [short documentary] 🔥

That's how large monolithic primary mirrors are often cast today.