Arecibo shutdown

The Big Bang 4 K radiation is an issue, since it comes from all directions. The 4 K black body radiation has the peak around 1 mm, so this affects the microwave reception.

For shorter wavelengths, the question is how many warm/hot objects are in the beam width. Ordinary stars do not radiate much in the far UV.

Welcome back. How long is your parole? ;)

Cheers

Phil Hobbs

Have you seen the movie from 2005? It's excellent in spite of it's short length.

It was on Hulu in 2013 but I don't know where you can view it now.

Nah, I haven't watched a movie in over 30 years, apart from a private showing of a documentary about the family of a good friend.

Cheers

Phil Hobbs

Futurama has a character Lrrr, ruler of the planet Omicron Persei 8, who wa tches an Earth TV series that, coincidentally, arrives at his planet 1,000 years after broadcast from Earth. When the show is interrupted by Fry (of course), 1000 years later Lrrr is infuriated and attacks Earth insisting th ey complete the performance. I'll let you find the rest. Lrrr likes to bi nge watch Friends too.

They will assume our civilization is going through that phase where it takes 25 years to evolve from OTA broadcast TV to a form of entertainment delivered over terrestrial links that's pretty much the same except you watch the shows on a computer. and you can pick what shows you wanna watch when.

The stripe of sky you can see varies with latitude like Cos(latitude) so near the equator is about as good as you can get for maximising utility. I think that finding a crater with almost the right shape played a part.

Think about what would happen at the pole...

The Greenbank telescope collapse (big steerable dish) was much more devastating. The observer in the control room was very very lucky!

The telescope sadly ended its life as a twisted heap of scrap metal.

They fixed it. Bigger and better

A considerable distance although if you knew that much detail you might well build a phased array to do it rather than use a single dish.

I'm not sure how they could be in that position since to know where to look someone would have had to tell them!

C&D are more or less the same problem and looking for stars where the radio emissions are distinctly non-thermal, polarised and have periodicities in the could be a frame rate zone of say 10-100 FPS would be good hunting territory. It also coincides with naturally occurring pulsars which when first detected at Cambridge were labelled LGM on the chart recording!

In actuality the pulsar surveys look for stuff on a much wider range than that since they don't know for sure what the ultimate bounds on pulsar spin rates actually are.

Millisecond pulsars were missed until the kit and inspired data processing improvements became good enough to see them.

Snag is that if we are any guide a civilisation will only be obviously radio bright from the point where they can build high power transmitters to the time when they master spread spectrum and fibre technologies.

I'm not sure how far out an Arecibo class telescope could detect a clone of itself if they were facing each other. The SETI guys have given considerable thought to exactly what frequency(s) to transmit on to get the greatest possible range and stand out as non-natural emission.

The so called "water hole" is a favourite for SETI transmissions and passive listening (on the assumption that all scientists think alike).

A narrowband CW signal with near 100% linear polarisation pulsed in a binary pattern will attract attention if seen by a scientist. Somewhere in the window between 1 & 10GHz being probably the optimum depending on the figure of the dish and the power of the transmitter.

I thought the hydrogen line at 1,420,405,751 Hz was the obvious choice:

More that they can build a bigger amplifier and dish than we can dream of - supposing that they choose to reply. Snag is that they might not transmit for very long and if nothing sensitive enough is looking their way we would still miss it even if it was a response to one of our signals.

Light travel time on a round trip for a msg is non trivial!

Arecibo has a more or less spherical reflector, so it doesn't give perfect focus in any direction, but on he other hand, allows moving the feed horn in a larger area and hence aim at different parts of the sky.

Special feed horns has been used at least with other spherical reflectors to improve the focus for instance with multiple feed horns to receive multiple geosynchronous satellites.

The Chinese instrument modifies the surface of the reflector so that is parabolic as viewed from the prime focus location, thus having perfect focus.

According to

If only approximate direction is known (say with constellation accuracy only) a phased array would be more suitable to create multiple simultaneous beams in real time. It is just a question of computational power to generate multiple narrow beams.

Alien reptiles intending to colonise the Earth and destroy US democracy clearly based their skin suits on that weird pale orange skin tone that US TV newscasters were clamped to on their approach the Earth.

The orange panda effect is surprisingly prominent on one such example!

It would have been more obvious if their skin flickered eerily between pale purple and sickly green like on the earliest NTSC transmissions.

Not really since although you can be pretty sure that radio astronomers will be looking at that line in detail there is a heck of a lot of neutral hydrogen in the galaxy so an artificial signal will be buried by the natural emmissions from the galactic medium. The "water hole" is between that line and the higher OH line at 1720MHz - bounded by H...OH frequencies.

If you wanted to stand out you transmit at high power on a non-natural frequency just far enough away to be at an insane Doppler shift but still well within the likely front end bandwidth of a receiver.

The quietest part of the radio spectrum is 1GHz to 10GHz carefully avoiding the obvious neutral H and OH molecular emission lines. Higher than that the microwave background swamps you and at lower frequencies everything in the universe is a thermal radio emitter mostly getting brighter as frequency decreases.

Photons above the UV Lyman alpha line do not get far before they encounter an atom of neutral hydrogen to ionise and get scattered and/or re-emitted isotropically in that rest frame. It leaves a signature of absorption lines in the light from the most distant objects.

Paul Horowitz went into detail about this:

A Laser seems to be the best choice.

That's exactly what I thought of when I realized I had it backwards.

Of course the instrument has to last that long. :(

Cheers

Phil Hobbs

It was too hard to move the bowl it is built in somewhere else.

-- A host is a host from coast to snipped-for-privacy@nrk.com & no one will talk to a host that's close.......................... Unless the host (that isn't close).........................pob 1433 is busy, hung or dead....................................20915-1433