I've read that after a signal candidate has been identified, the same point in the sky is later revisited to verify the signal is really there. If not, it's considered anomalous and rejected.

What I'm wondering is, what if it's a moving signal source, traversing across our sky. What if it's an alien space probe similar to Pioneer 10 or Voyager I and II. Will we ignore such a signal just because it won't hold still? Is there any possibility of mining the data to look for a moving target?

On a similar note, it seems that any signal source on a rotating planet would come and go. Wouldn't a signal from us appear as a short flash every 24 hours? Are these candidate signals viewed for long enough for a planet-bound transmitter to rotate back into view?

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> I've read that after a signal candidate has been identified, the same point in
> the sky is later revisited to verify the signal is really there. If not, it's
> considered anomalous and rejected.
>
> What I'm wondering is, what if it's a moving signal source, traversing across
> our sky. What if it's an alien space probe similar to Pioneer 10 or Voyager I
> and II. Will we ignore such a signal just because it won't hold still? Is
> there any possibility of mining the data to look for a moving target?
>
Yes, if the detected signal does not persist among several visits, it is discarded as a possible source. However, a moving target would have to move a LONG distance before it is considered moved to the telescope.

Using the information provided about calculating smallest resolvable angle, Arecibo's diameter (305m), and the wavelength we look at (~1.5GHz), we can see that under perfect and theoretical conditions, Arecibo can seperate two objects if they're at least 0.1652 arcseconds apart. Do some trig to see how far a signal needs to move before it registers at distances of 4.3 light-years (our nearest neighbor star), 10 lightyears, and 100 lightyears =)

In practice though, according to this site, Arecibo can only pull off 50 arcseconds of resolution @ 5GHz. This makes the distance an object needs to move a WHOLE lot bigger, and at the stellar distances we're talking, an object would be still for all intents and purposes.


> On a similar note, it seems that any signal source on a rotating planet would
> come and go. Wouldn't a signal from us appear as a short flash every 24
> hours? Are these candidate signals viewed for long enough for a planet-bound
> transmitter to rotate back into view?
>
>
It depends on the source. A very high power source that was aimed at us would indeed seem to turn on and off. However, SETI is sensitive enough to detectet just the background noise of a planet caused by all the aliens hair driers (...if they have hair :D) and such at a reasonable distance. This signal will remain constant assuming the planet has inhabitants all the way around it.


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Thanks Puffy! [/url]