Arecibo shutdown

I followed links from there to a much bigger and shinier radio telescope in China, apparently finished and ready, but nobody wants to work there.

Claude Bernard is a piece of shit.

Steve Wilson wrote: z.

** So who is listening for "little green men" now ?

..... Phil

Something farther from the equator could scan a lot more sky even if was also a stationary dish. Why did we put it in Puerto Rico?

Really? How does that work exactly?

--

Rick C. 

- Get 1,000 miles of free Supercharging 
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No one. Once the little green men found and capruted Jan, they took a hyperspace jump back to Omicron Persi 8.

Cheers

Probably, cost. It's built into a natural cavity in the ground. I believe the new Chinese instrument is constructed similarly.

An aside: Over what distance could two Arecibo-like instruments communicate if A) they knew where to look and what to look for B) they knew only where to look, but not what to look for C) They knew not where to look and not what to look for D) they knew not where to look, but did know what to look for

The answers doubtless depend on time allocated to the search. Let's assume 50 years, the approximate life of the instrument.

I've done a little web-surfing and found no explicit discussions. The answers might have some bearing on Fermi's paradox.

Thanks for reading and any insights,

bob prohaska

25 light years out and 25 light years back, assuming you got an immediate reply?

Then number of star systems within 25 light years isn't large. I think it may be indirectly confirmed there's no advanced technological civilizations on any of 'em we would have heard them by now.

"Horowitz and Sagan (1993), reporting the results of a five year all-sky survey, concluded that there are no Kardashev (1964) Type I civilizations (isotropically transmitting ?10^13 W) within 25 light-years of the Sun, no Type II within 2500 light years....and those bounds should be tightened considerably in the coming years"

The reply from even a Type I civilization (which is far more advanced than ours), that wished to communicate, would not be subtle when it arrives. The ability of a civilization to pull signals out of the noise and return the call massively amplified likely scales with the civilization.

If and when a civilization like that picks up our lil signal and they decide they have something to say in response, when the reply come back no one's going to be mistaking it for anything other than what it is.

My mistake, communications was a dumb constraint 8-(

Let's just suppose we're searching for a signal, from somebody with instruments like ours. No constraint on when they did the sending, could be a billion years ago. Easy case first, we happen to guess right on which direction to look and what kind of signal they are sending. How far away could they be and still have enough "brightness" against the background noise to be recognized using 50 years of receiver data?

Probably there should be a constraint on the baud rate, but I'm not sure how to word it. Maybe ten bits with 95% confidence? It does seem intuitive that fast signals are harder to recognize than slow.....

Thanks for reading,

bob prohaska

After further consideration I suppose it would be about the same, just more above the ecliptic and less below..

RIP. Aricibo was one of the things that encouraged me to study astronomy. They did a lot of cool stuff there.

Cheers

Phil Hobbs (B.Sc. Astronomy & Physics, UBC '81)

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
http://hobbs-eo.com

It is possible to calculate that using Shannon's formula, and it is also possible to calculate how much a signal attennuates when travelling over a distance. The amount of noise in the receiver and the background noise in the universe can be measured. Ther also is the "gain" of the transmit- and receive antennas, which is the inverse of the solid angle that the antenna illuminates (a high antenna gain means there is a small solid angle so you need better pointing accuracy).

From those formulas and parameters you can calculate how much power you need to transmit a certain number of bits/s over a certain distance. Engineers make such calculations when designing communication systems, e.g. for spacecraft like Voyager. And they design their systems in such a way that they can lower the bitrate over time to compensate for the increased distance.

You seem to assume that "an advanced civilization" means that it has found how to defy the laws of nature. Or that has other laws of nature.

Shannon tells how many bits/s can be transferred with a specific bandwidth and S/N ratio.

The Friis equations

tells the expected received power, when both antenna aperture areas, distance between antennas and wavelength is known.

When looking at the formulas for a point-to-point link the shorter the wavelength the better. Thus gamma or X-ray frequencies should be used. Unfortunately, the galactic hydrogen attenuates much of the wavelengths below 91 nm, so slightly longer wavelengths should be used in UV-C.

Two Hubble size (2.5 m) telescopes could maintain a quite long distance link.

The Arecibo size but only a few GHz reflectors are quite inadequate for interstellar communication.

An advanced civilization interested in UHF/microwave could build much larger antennas, especially if their gravitation is low (or using orbital dishes).

Instead of using one large dish, it is better to use a huge array of smaller dishes as a phased array. With sufficient computational power, instead of generating only a single very narrow beam from the multiple antennas, a huge number of individual beams can be created to monitor multiple direction at once, as long as the narrow beam is within the relative wide beam of each smallish reflector.

If the advanced civilization has a energy source and could use, say 1 GW, for each antenna in a huge antenna array, a single very narrow but extremely powerful beam could be created.

The above doesn't violate any laws of physics and also the human kind could be capable of it in a century.

Steve Wilson wrote in news:XnsAC7AB6702DD0Didtokenpost@69.16.179.22:

short url

"Tom Del Rosso" wrote in news:rp8e8o$gfm$ snipped-for-privacy@dont-email.me:

+1

And even from other ages. Binge watching a series is fun.

Try Lexx, for example. Some of the episodes after they came to Earth are pretty funny.

Martin Riddle wrote in news: snipped-for-privacy@4ax.com:

Phil Hobbs wrote in news: snipped-for-privacy@electrooptical.net:

Hahahahahaa! Watch put for his noodly appendages!