Why Do Spinning Liquids Make Great Telescopes?

Why Liquid Mirrors Make Great Telescopes

[TheActionLab]

At 2:17 and 2:23 I accidentally say it backwards. I should have said the faster I spin it *the shorter* the focal length not longer. Shorter focal lengths give the wide angle view.

[andrewparker]

I visited the mirror making lab at the University of Arizona and they actually use this exact technique to speed up the manufacturing process. They pour liquid glass into a rotating mold, and as the glass cools it forms a more or less perfect parabola. They then use traditional sanding techniques to grind out any imperfections until the mirror is basically perfect

[veryblocky]

That demonstration with the blue water in a parabola was really cool

[thomasherbig]

This principle has revolutionized the production of very large telescope mirrors. Most 8-meter mirrors (that's huge professional-size) are made by rotating the furnace with the molten glass and slowly cooling it down. The mirror blank then solidifies into a paraboloid. It still needs some grinding, but the process is many times cheaper than traditional methods.

One quibble: faster rotation results in a shorter focal length, not a longer one.

[Briaaanz]

The amount of knowledge humanity already possesses about the cosmos is both humbling and awe inspiring

[ProjectPhysX]

There is a similar technology called liquid lenses. There you have two transparent oils with different refractive index in an electric field, and based on the voltage the interface between the two oils bends differently and acts like a lens. This was used in some early autofocus webcams back in the day.

[FredMcC]

Sooo jealous of the fact kids of today get to have this guy be a thing! The content he covers, as well as the simplistic yet somehow still extremely informative without being dumbed-down method in which he presents it, is all very captivating and attention-grabbing. Give this guy a catchy stage name and a show on PBS, he could easily be this generation's Bill Nye-Already is, if you ask me.
Not that he could ever replace Mr. Nye, but it would've been killer to see these things when I was a kid.
*Bursts into room* "MOM, WE NEED SOME GALLIUM!"

My fingers are crossed that I can get my son or daughter into this channel.

[bluustreak]

Another advantage is that any dust would go to the edge of the spinning mirror due to the radial force :)

[winklethrall]

After reading about liquid metal telescopes in a science magazine about 40 yrs ago, I obtained and kept a 10 lb bottle of mercury around hoping to one day build one. As I got older, my sense of responsibility outpaced my scientific ambitions and I took it to a mercury recycling center.

[nitinb]

The simplicity of explaining the complexity of scientific theories is what drives me towards this channel. Keeps the science kid in us alive even at my age. Thanks to the team at Action Lab.

[tednoob]

I've never thought about the difference between lenses and mirrors before, but you're right. Light should reflect the same regardless of the wavelength, while different wavelengths refract differently.

[Poult]

I used this technique with epoxy resin to make a parabolic reflector for a microphone. The surface finish was not good enough for optical work but at audio frequencies it is perfect. Much like radio telescopes do not need optical finishes.
Great channel!

[andnat]

This is super cool! I understand how it is simpler for this to be pointed straight up, but it would be really cool to see how it would look if you were able to put this in some ‘hypothetical’ centrifugal device, so that with a slow motion camera, and some clever stabilization, editing, it would be pretty cool to see if that could work.

[RGAstrofotografia]

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.

[danielbickford]

I'm kind of curious if you could spin up your liquid telescope up to speed and get it to the right shape and then flash freeze it so you can then point it at other directions?

[dumbguyy]

I’m pretty sure they do something like that for very large telescopes. They spin molten glass to get it into the general shape.

[adayoff]

Dude your way too cool for school. I wish I had a friend like you that I could talk to about obscure concepts, philosophy, science and crazy
"what if's" that 95% of my social circle just doesn't get or see any benefits in discussing.... Just for shits and giggz. Even better then getting outta the house to try to find and experiment to demonstrate what ever it is we were talking about. Thanks for sharing your valuable time knowledge and positive energy with the world. I hope our paths crossed some day

[postal_the_clown]

Just a thought. Maybe your light source could have been projecting a simple shape like a triangle or 5-point star to enhance the resolution of the object and demonstrate the affect of the imperfections of the gallium/turntable.

[nicky]

Could you build a mirror like that using a low melting point metal, spinning it while in liquid state and then retire the heat source while still spinning, so it can retain the shape? Then you can coat that with any silvery sustance to make it reflective, just like mirrors are built out of regular glass.

[physforfun]

Great video! Actually I knew about the parabolic shape of spinning fluids from my old text book in fluid dynamics, but that they in fact used this phenomenon in telescopes was amazing! Thanks for great video and explanation, keep up the good work! 🤓