Will the Aliens hear our Radio and TV broadcasts ?

[Ainsley]

Ive often heard it said that our Radio and TV broadcasts could be picked up by "Aliens", so they could be listening to our planet long before they ever visit.

However, I have heard the radio broadcasts made by the Apollo missions and they were pretty low quality even though they were just on the moon.

I also fail to get radio stations in my car/home from far away places and thats just on our planet.

Now, I know our planet is round, radio waves may get blocked by hills, atmoshphere etc, but even so, I struggle to see them being powerfull enough to be picked up in our Solar System, let alone in another star system.

Would our broadcasts just be too faint, distorted and crowded out by noise pretty soon after leaving our solar system ?

Would they degrade over distance ?

Just how many star systems would they have reached given the first commercial radio broadcasts started in the 1920's ?

[Paul M]

Radio listeners in the region of Aldeberan will be tuning in to BBC World Service coverage of WW2. I'm sure the signal will get that far because back then they used thumping great transmitters at various frequencies.

These days, many of our transmissions are more discrete. As the radio spectrum becomes more congested there are far fewer big powerful transmitters.

So rather than have a few broadcasts that were very prominent we now produce more of a low key cackle of digital and analogue signals that are directed to their audience more accurately. Probable less penetrating to interstellar space.

[mallorcasaint]

It's highly unlikely. Any intelligent life would need to be looking (or listening ) in exactly the right place and the signals would be extremely weak (inverse square law) and probably fragmented. Our nearest star other than the Sun is Proxima Centauri at 14 million light years and the huge distances mean the odds of pinpointing and receiving a signal are minscule.

[JulianO]

Radio wave intensity falls off with inverse square law, so every doubling of distance it is 1/4 the power.

However that said, if they are anything like us, they will have very powerful radio telescopes aimed at detecting faint signals.

This page http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/980123d.html lists some stats and estimates 14,600 stars within 100 light years (roughly the time above).

[Ainsley]

So 14 million years later, someone "could" pick up our signals if they look very carefully then.

Given that what are SETI hoping to find ?

[Cath]

Our nearest star other than the Sun is Proxima Centauri at 14 million light years.

I'm sure you really meant to say about 4.3 light years away

[Ainsley]

Oh, 4.3 years is slightly better then. So they will have time to watch/listen and respond then.

[mallorcasaint]

I'm sure you really meant to say about 4.3 light years away

OOPs! Yes! My bad!

Of course by the time the signal reached them it would be incredibly weak and they would need a vast antenna to receive it. Interesting view on it here: http://news.bbc.co.uk/1/hi/magazine/7544915.stm

[Ainsley]

Good artical - poor result thought:

Shostak calculates that Nasa's recent broadcast of Beatles music towards Polaris, the North Star, using a 210ft antenna and 20kW of power, would require any potential aliens to have an antenna seven miles across to be aware of it. To actually receive it as music, this would need to be increased to a 500-mile wide antenna. Polaris is 430 light years away.

So basically we are not likely to be heard or seen.

Thats a shame.

[Cath]

The easiest signals from us they could probably receive are our RADAR pulses from things like ships, aircraft, space RADAR etc, they tend to be very well concentrated into narrow beams and are many kilowatts focused by parabolic reflectors (maybe mega watts ERP) and swept right across the horizon 24/7.

[Cath]

Shostak calculates that Nasa's recent broadcast of Beatles music towards Polaris, the North Star, using a 210ft antenna and 20kW of power, would require any potential aliens to have an antenna seven miles across to be aware of it. To actually receive it as music, this would need to be increased to a 500-mile wide antenna. Polaris is 430 light years away.

I would imagine for any 'advanced' civilizations out there that really do want to find others (as we do) then I would have thought it a simple matter for them to build radio antennas (or the equivalent of) many miles across that orbit their own star or such like. I don't think it would be hard for them to do if they had really got the hang of moving about their own solar system with ease, their's more than enough materials available in any solar system.

[mallorcasaint]

Lets just hope they don't get Jeremy Kyle first!

*Apologies for triple post earlier!! Don't know what happened.

[mallorcasaint]

I would imagine for any 'advanced' civilizations out there that really do want to find others (as we do) then I would have thought it a simple matter for them to build radio antennas (or the equivalent of) many miles across that orbit their own star or such like. I don't think it would be hard for them to do if they had really got the hang of moving about their own solar system with ease, their's more than enough materials available in any solar system.

Yes but they would need to be looking at exactly the right point in space which the odds of probability say would be nearly impossible, unless they already knew we were here.

[Tinker1947]

Proxima Centauri, 4.24LY's

http://en.wikipedia.org/wiki/Proxima_Centauri

[Cath]

Well, personally I greatly suspect their are far more efficient ways to communicate across vast distances that we no doubt can't even imagine as yet. It's only been very recent that we have discovered and almost mastered radio communication.

[Tinker1947]

Seems there's a bit of lag on the internet, got a double post.....

[Tinker1947]

Seems there's a bit of lag on the internet, got a double post.....and this one...

[endure]

The easiest signals from us they could probably receive are our RADAR pulses from things like ships, aircraft, space RADAR etc, they tend to be very well concentrated into narrow beams and are many kilowatts focused by parabolic reflectors (maybe mega watts ERP) and swept right across the horizon 24/7.

The ships I sailed on had 60KW 'S' band radars. Their ERP was about 12 watts as they were pulsed.

[Cath]

Yes but they would need to be looking at exactly the right point in space which the odds of probability say would be nearly impossible, unless they already knew we were here.

I suppose they could build as many as they like, could build a whole ring of them (many 1000's of receivers/antennas) in an orbit centered around their planet(s) or sun.

[Cath]

The ships I sailed on had 60KW 'S' band radars. Their ERP was about 12 watts as they were pulsed.

The average power would be low but the pulses themselves would be very high ERP.

[mallorcasaint]

Proxima Centauri, 4.24LY's

http://en.wikipedia....roxima_Centauri

Yes I did correct that

[mallorcasaint]

The average power would be low but the pulses themselves would be very high ERP.

The energy content of the pulse is equal to the peak (maximum) power level of the pulse but as the measurement is over a longer period than the pulse duration it's referred to as average power.

[mallorcasaint]

I suppose they could build as many as they like, could build a whole ring of them (many 1000's of receivers/antennas) in an orbit centered around their planet(s) or sun.

The distances are so vast that even that would be hit and miss.

[moogoomonkey]

I'm sure Proxima is circa 4.3 LY away?

[ollypenrice]

It's highly unlikely. Any intelligent life would need to be looking (or listening ) in exactly the right place and the signals would be extremely weak (inverse square law) and probably fragmented. Our nearest star other than the Sun is Proxima Centauri at 14 million light years and the huge distances mean the odds of pinpointing and receiving a signal are minscule.

A bit nearer, I think. 4.24 LY or so? Not that it matters much.

The real issue, I think, is that intelligence can mean something entirely different from what we think it means. Hollywood loves to make little creatures just like us but with pointed ears and green skin - who might have some notion of what World War Two was all about. However, an entirely different kind of intelligence might not interact with our kind of intelligence at all. Genetically my dog and I parted company no more than a few seconds ago in the greater scheme of things, having shared a common ancestor. We are almost the same creature. Four legs, two eyes, two ears, a skeleton with broadly the same structure and pentadactyl limbs. But what does she know of World War Two? And what is worth knowing about it, for that matter? Apart from the fact that humans orchestrated it with their phenomenal intelligence.

Olly