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Comment by throw0101a | Hacker News Reader

Tom Scott did a video on the ELT about a month ago:

* https://www.youtube.com/watch?v=QqRREz0iBes

Most of the video is an explanation of (a) why ground-based telescopes are still useful, and (b) why ganging up multiple telescopes (to create a large 'virtual' area) only goes so far, and then he gets into the ELT in part three of the video.

It's big. The scale is remarkable.

View on HN

I think its total mirror area is more than that of all existing (largest) professional reflecting optical telescopes combined

39.3m aperture, mirror area scales quadratically with that https://en.wikipedia.org/wiki/Extremely_Large_Telescope

https://en.wikipedia.org/wiki/List_of_largest_optical_reflec...

https://en.wikipedia.org/wiki/List_of_large_optical_telescop...

I love their naming sense.

Very Large Telescope

Extremely Large Telescope

Overwhelmingly Large Telescope

next should be called 'Such Telescope' and 'So much Telescope wow'

Definitely A Telescope

Relevant: https://maz.one/insanely-large-machines.html

Chonky boy Telescope

Telescope AF

Oh lawd he comin

It follows how frequency band called

Presuming economical access to space is going to scale up a lot in a few years, and taking the many billions of dollars, years of building, and human obstacles to building on the ground -- if it were me with the billions, I'd be thinking about creating a workshop in orbit and then building genuinely big scopes up there, where you're so much less constrained by "the whole thing's gotta fit in a booster, survive not just Earth gravity and weather but a rocket launch, and then deploy and totally work up where nobody can fix it."

> why ground-based telescopes are still useful

Any layman reading on why optical interferometry hasn't been solved for astronomy, and what it'll take to get there?

Light wavelengths are in the order of nanometers. Radio wavelengths (were interferometry is "solved") are in the order of kilometers to centimeters. While it is possible to build structures that are unmoving in the order of centimeters, it is hard to impossible to do that in the order of nanometers. That doesn't make direct optical interferometry impossible, just quite a bit harder, see e.g. LIGO.

And for doing timing-based interferometry over a distance, the needed timing precision limits your resolution. 1km/c is in the order of 10^-6s (µs), "easy", 1cm/c is in the order of 10^-11s (ps) "possible", 1nm/c is at 10^-18s (as) "quite impossible".

And for the layman, a factor of 10^-6, or 6 orders of magnitude in time are like "a second to two weeks" and "two weeks to far back into the stone age".

Phenomenal explanation. Thank you!

> 1km/c is in the order of 10^-6s (µs), "easy", 1cm/c is in the order of 10^-11s (ps) "possible", 1nm/c is at 10^-18s (as) "quite impossible".

Wow. That's really sad that the orders of magnitude in resolution required escapes beyond our limits of detection.

What do you mean by solved ? optical interferometry exists since the 70s, and is used a lot. The VLT, Keck observatory, CHARA, LBT, NPOI. It's not has big as classical observation because there are a lot of disadvantages, but it exists

I think the neatest part is fluid floating, and having to time the light physically because there is STILL too much data to convolve it in real time.

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