This Toxic Liquid Telescope from the 1850s Is Finally Useful

Sometimes looking into a pool of a toxic liquid holds the secrets of the universe–or maybe just this one time.

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[jmanj]

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

[trissylegs]

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.

[markholm]

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.

[orbemsolis]

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!

[gowzahr]

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.

[markholm]

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.

[jasonvanpelt]

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

[stevejohnson]

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.

[Brook_tno]

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

[anthonynarozniak]

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

[markholm]

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.

[agmuntianu]

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 .

[MrRedwires]

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 <3

[Oneflyingmonkey]

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.

[BrttM]

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.

[rodbotic]

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.

[clf]

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

[tozzasque]

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

[manualdidact]

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.

[baldeepsingh]

Hey, I am an astrophysicist working on the ILMT with Dr Paul Hickson. Hoping to get data very soon! Very Excited!