Comment by SiempreViernes | Hacker News Reader

Comment by SiempreViernes | Hacker News Reader

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Arecibo has been superseded in terms of raw aperture by FAST, and in terms of angular resolution by the interferometry arrays since 1966 at the latest when the One Mile observatory was doing 23 arcsecond resolution images. I think it's main somewhat unique capability was doing radar measurements of things in our solar system.

My impressions is the neglect comes from having done all the useful things it could do ages ago, and not finding anything new to help with in the areas of science that gets funding.

The state of the art interferometry arrays are ASKAP and MeerKAT currently, in the sense of being the newest and being precusors of the SKA which is the biggest project right now.

In terms of best in class, it varies with the specific frequency and which bit of the sky you want to look at and also with what you consider an observatory: the Event Horizon Telescope that resolved the M87 black hole has the worlds best resolution at their mm wavelengths, but it's really a bunch of existing telescopes collaborating and not a purpose built facility.

I'm too sad today to engage with this, but you're simply wrong about Arecibo "having done all the useful things it could do ages ago, and not finding anything new".

Here, for example, is Arecibo on the cover of Nature, in 2018: [1]. And you might want to look into NANOGrav [2]: you'll be hearing a lot more about it (I promise) in one or two years, depending on publication timelines.

[1] https://twitter.com/nature/status/951423495107481602 [2] http://nanograv.org/

Despite its large instantaneous sensitivity, Arecibo is not really suited for transient work. In the FRB example Arecibo has a factor 22 advantage in collective area and yet trails Parkes by a factor of 14 in number of discovered FRBs: weak evidence of a unique capability.

And it's too bad the NANOGrav risks getting its results delayed by the inability to extend observations on half its sources, but the loss of Arecibo will not doom the entire project: again not conclusive proof that Arecibo added a unique capability.

There is a sea of difference between your initial statement of "having done all the useful things it could do ages ago, and not finding anything new" and your new statement of wanting conclusive proof that Arecibo has "a unique capability".

The "proof" shows Arecibo was still very useful and finding new things and this disaster will significantly delay research. (As a side note; delays in research can easily mean the death of that research as funding is often time-bound)

Somewhere in this there is a larger story of useful projects not receiving enough funding because they aren't sexy enough.

What's your connection to NANOGrav?

Interferometry can simulate the resolution of a dish corresponding to its baseline but not the sensitivity.

The VLA may simulate the resolution of a 36 km dish, but it has the sensitivity of a 130 meter one, considerably less than Arecibo's 305. You're ultimately limited by signal vs noise and can't make up for the receiving area that simply isn't there, no matter the width of the baseline.

This makes interferometers and stationary giant dishes different tools, suited to different types of observations. Arrays are not good at imaging extended diffuse sources.

Am I wrong but I remember something that it's resolution sucks because it's not parabolic.

May be true, but its real value was has a radar.

The transmission capability is part of the reason Arecibo would be so difficult to fix. The platform is almost 900 tons.

China's FAST telescope was designed without transmit, mostly to save on suspended weight. Its focus cabin is only 30 tons.

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