A message from aliens!!!

[vbloke]

http://mysterytopia.com/2008/08/radio-signal-detected-from-beyond-solar.html

Remember that WOW signal detected by SETI (Search for Extra-Terrestrial Intelligence) from 1977? The signal, witnessed by a project volunteer, was so strong that he quickly circled the indication on a printout and scribbled the phrase “Wow!” in the margin. Dubbed the Wow! signal, it's considered by some to be the most likely candidate from an artificial, extraterrestrial source ever discovered, but it's never been detected again. And now this. A Durban University of Technology teacher and his students have apparently found the first radio signal from outside our Solar System, possibly from an alien source. Yes, you read it correctly the first time, but go ahead, read it again.Another one:
Before you read on, I'll remind everyone this ...Gliese 581 has planets in the habitable zone, which is also in the constellation Sagittarius, the very same constellation where this signal came from. From: http://aliencasebook.blogspot.com/2008/08/first-radio-signal-detected-from-beyond.html

The actual story is a tad more mundane...
http://www.dut.ac.za/DealerNews/newsdetails.asp?newsitem=3197

Basically, they made a homemade radio telescope and pointed it a a known radio source at the centre of the galaxy... Sagittarius A*
No aliens needed...

[Mulder]

I think the story may have got garbled because they are using the Hydrogen Line, which is the same frequency that is widely used on SETI. I've always thought the logic that aliens would broadcast at that frequency a bit dubious, but what do I know.

[Cuddles]

A Durban University of Technology teacher and his students have apparently found the first radio signal from outside our Solar System

No they haven't.

[ZERO]

Do the SETI people look for signals that are deliberately broadcast to be picked up by other civilizations or are they looking for TV/radio unintentional signals?

What if every civilization is listening but not actively sending signals?

How far can TV/radio signals actually travel?

[Matt]

Do the SETI people look for signals that are deliberately broadcast to be picked up by other civilizations or are they looking for TV/radio unintentional signals?

Either


What if every civilization is listening but not actively sending signals?

Then we won't see each other. However I guess you meant to say every civilisation except us.


How far can TV/radio signals actually travel? Theres no upper limit but the signal strength gets weaker with the square of the distance.

[ZERO]

Then we won't see each other. However I guess you meant to say every civilisation except us. Are we transmitting "anybody out there" signals?
I did not know that.


Theres no upper limit but the signal strength gets weaker with the square of the distance.I thought radio waves stretch out and change over long distances?
I don't know much about it. :-[

[farmersboy]

I wouldn't have thought that we need to specifically send an 'is there anybody out there' signal - there must be enough 'noise' being sent out into space that is disdinguishable from natural background noise that someone somewhere would recognize as artificial.

The problem is of course that such noise may not have reached anyone or anything yet, given the vast distances it needs to travel...

[Matt]

Are we transmitting "anybody out there" signals?
I did not know that.

No but we're not doing anything to ensure that our TV radio and data signals don't escape.


I thought radio waves stretch out and change over long distances?
I don't know much about it. :-[

They do strech out as they climb out of our gravity well, and also as they climb out of the sun's gravity well.

Then they might well be unstreched as they fall down the gravity well of the receiving planet.

However what I think you're talking about is the other redshift. Caused by our relative speed with regard to other systems. If we're approaching another star system our radiowaves will appear shrunken to them. (blue shifted) If we're receeding, our radio waves will appear streched out. (red shift)

It just so happens that as the universe is expanding, there's a tendancy for distance to relate to the relative speed. The further away something is, the faster it will tend to be receeding from us. Therefore the further away an object is the more it will tend to be redshifted.

However this isn't something that happens gradually as the radio wave travells through space. It's not a contiual process that has cummulative effects adding up more and more as it travels further. It's something that happens when you switch your point of view frame of reference, to another.

When this was first observed, the expansion of the universe was just one of a number of theories put forward to account for this observation. Tired light theories considered that the light might be being affected in the manner of gradually being streched out as it travelled. However the expanding universe one the day by virtue of having evidence to back it up, and being able to reproduce the effect in the lab.

Either way however a streched out out radio wave is still a radio wave. When we point our radio telescopes at a distant source we already know how streached waves from that source are, and so it is the streched out waves that we're looking for.

[ZERO]

They do strech out as they climb out of our gravity well, and also as they climb out of the sun's gravity well.

Then they might well be unstreched as they fall down the gravity well of the receiving planet.

However what I think you're talking about is the other redshift. Caused by our relative speed with regard to other systems. If we're approaching another star system our radiowaves will appear shrunken to them. (blue shifted) If we're receeding, our radio waves will appear streched out. (red shift)

It just so happens that as the universe is expanding, there's a tendancy for distance to relate to the relative speed. The further away something is, the faster it will tend to be receeding from us. Therefore the further away an object is the more it will tend to be redshifted.

However this isn't something that happens gradually as the radio wave travells through space. It's not a contiual process that has cummulative effects adding up more and more as it travels further. It's something that happens when you switch your point of view frame of reference, to another.

When this was first observed, the expansion of the universe was just one of a number of theories put forward to account for this observation. Tired light theories considered that the light might be being affected in the manner of gradually being streched out as it travelled. However the expanding universe one the day by virtue of having evidence to back it up, and being able to reproduce the effect in the lab.

Either way however a streched out out radio wave is still a radio wave. When we point our radio telescopes at a distant source we already know how streached waves from that source are, and so it is the streched out waves that we're looking for.

Thanks, very enlightening. O0

[Croydon Bob]

Is it an Urban Myth that the first TV broadcasts powerful enough to be sent into outer space and currently 70 light years away were broadcast by Nazi Germany? I hope it isn't true.

[Matt]

Is it an Urban Myth that the first TV broadcasts powerful enough to be sent into outer space and currently 70 light years away were broadcast by Nazi Germany? I hope it isn't true.

Well I did a little research. The first thing I noted was that I think that any broadcast is powerful enough to be sent into outer space. Certain longwave trasmission may be reflected off the ionosphere but that asside I fail to see any distinction.

What more regualr AM radio preceded all of these transmissions by a number of decades. An aleine civilisation's first encounter with our tranmissions is more likely to be the shipping forcast.

Wiki gives us a timeline for TV
http://en.wikipedia.org/wiki/History_of_television#Broadcast_television
http://en.wikipedia.org/wiki/Timeline_of_the_introduction_of_television_in_coun tries
So nazi germany wasn't the very first but it was among the first.

Just in case you think that power is an issue you might want to look inot the different frequncies and signal strengths of these preceeding transmission to see if there's nay discernable difference that might validate this urban legend.

[Cuddles]

Is it an Urban Myth that the first TV broadcasts powerful enough to be sent into outer space and currently 70 light years away were broadcast by Nazi Germany? I hope it isn't true.

Firstly, as Matt has said, any broadcast is strong enough to reach outer space, and indeed anywhere in the universe. The power obeys the inverse square law, so they may not be distinguishable from background noise after a certain distance, but that will depend on local conditions and may be dependent on technology, so there is no clear cutoff after which a signal will not be detectable.

Secondly, although there's no hard and fast definition of "outer space", the generally accepted definition uses the ionosphere as the boundary, although whether the ionosphere itself is included varies. That means outer space starts somewhere between 100km to a few thousand km above the Earth's surface, which means even the very first radio signals were easily strong enough to be detectable from outer space.

I suspect what the urban legend is meant to refer to is signals which would be strong enough to be detected at a particular distance using our current technology. I have no idea whether Nazi signals would be the only ones detectable at 70 light years, but I suspect not. I also suspect it sounds a lot less impressive when you put it like that.

[edd]

Is it an Urban Myth that the first TV broadcasts powerful enough to be sent into outer space and currently 70 light years away were broadcast by Nazi Germany? I hope it isn't true.

A typical modern TV transmitter is about a megawatt (equivalent isotropic radiation). At 70 light years radius there's a surface area of 5.5x1036m2. That's about 2x10-31W/m2.

The SKA - Square Kilometre Array - hasn't even been built yet and that's got a sensitivity of about 10-29W/m2.

So I don't know how powerful Germany's transmitter was, or how big ET's radio telescope is (but I'd be awfully jealous if they they had one bigger than the SKA), and I've ignored some other things which probably put those numbers off by a factor of a few, but I doubt very much any aliens would be able to pick up Hitler today.

You'd have been able to detect it from around 5 light years away I guess, but 70 - I'd be skeptical.

[Matt]

A typical modern TV transmitter is about a megawatt (equivalent isotropic radiation). At 70 light years radius there's a surface area of 5.5x1036m2. That's about 2x10-31W/m2.

The SKA - Square Kilometre Array - hasn't even been built yet and that's got a sensitivity of about 10-29W/m2.

So I don't know how powerful Germany's transmitter was, or how big ET's radio telescope is (but I'd be awfully jealous if they they had one bigger than the SKA), and I've ignored some other things which probably put those numbers off by a factor of a few, but I doubt very much any aliens would be able to pick up Hitler today.

You'd have been able to detect it from around 5 light years away I guess, but 70 - I'd be skeptical.

Well I guess it's a little anthropocentric to limit these hypothetical aliens' technology to our own achievements.. After all the sensitivity of our recievers telescopes have come on leaps and bounds in those 70 years. Imagining that someone might have a receiver hundreds of times more sensitive than what we're currently building is not too far fetched.

A more practical limit might be signal to noise ratio.