This Toxic Liquid Telescope from the 1850s Is Finally Useful

Large modern mirrors are made using the same principles as this liquid mirror. They melt glass in a spinning kiln, and rotate it at a constant speed until the glass sets and is annealed. This cuts out a large portion of time needed to polish the lens to its final shape.

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..

10/10 closing pun

Surprisingly good pronunciation of Dunedin. American tourists here often seen to have entertaining amounts of trouble with it.

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 a lovely ending phrase :)

Very nice of you to mention the Man from Dunedin New Zealand.

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.

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.

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.

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

Wow I got that the secret is the spin almost immediately at the beginning of the video. I felt so intelligent 🥳❤️

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.

Another big problem that you didn't mention is the mirrors and lenses get so big that they deform under their own weight

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.

Stuff like this is the “hold my beer” of science and engineering

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!

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 Youtube videos of the process.

"Less than one tenth the cost". Outstanding!!
You just made my day by not saying, "More than ten times less".

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.