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Extraterrestrial (ET) signal detector

"Blinking" Sun would advertise ET
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(+6, -1)
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Why should ET (i.e., any sufficiently advanced extra solar civilization) bother with broadcasting on a narrow beam (SETI style) when he/she/it can essentially put a blinking light in the window of the universe?

There are a couple of ways to do this: Put some big light-blocking satellites in orbit abound the sun spaced at a distance of 1, 3, 5 and 7 (thousand miles perhaps). The sun will dim at a 1, 3, 5, and 7 non-natural period as long as the satellites are orbiting at the same speed and in the same plane. This periodic dimming is how they actually detect extra-solar planets transiting the extra-solar sun.

Alternatively, put a big satellite in orbit that that has two discs rotates rotating in opposite directions where the discs are perpendicular to the surface of the sun. Have the discs with a "cut out" that lets sunlight through at 1, 3, 5, 7 intervals so that the sun brightens in a non-natural period. (Think massive stroboscope).

These suns would be easy to detect, since all you have to do is record the light from a galaxy over a let's say a 100 minute interval with a filter being present at 1, 3, 5, and 7 minute intervals and subtract the light digitally from a photo of a galaxy where the "control" 100 minute exposure is recorded continuously. The only stars that would be left on the exposure are the ones blinking at non-natural intervals.

The nice thing about this set up for ET is that it does not require a continuous power source (free broadcasting once the satellites are in orbit), it broadcasts on "all" channels and is not affected by red-shift. There is no need for technology any more advanced than what we already have-- just a bunch of wampum.

In theory, you can set up this detector in your backyard. All you need is a telescope, CCD camera and computer with digital imaging software. The tricky bit is timing the capture of images for all of the possible 1, 3, 5, and 7 intervals.

Any thoughts?

If you detect ET, I'll bet there is a Nobel prize waiting for you.


PSYKL, Oct 06 2009

(?) Intergalactic Morse Code Intergalactic_20Morse_20Code
[theircompetitor, Oct 09 2009]


       Is this patentable?
PSYKL, Oct 08 2009

       Most species are worried about themselves. Putting up big satelites/stroboscopes just to signal presence but not send information seems a bit short sighted. Any ET signal is most probably going to be a conversational broadcast.
wjt, Oct 08 2009

       If I understand this right, perhaps this is precisely what we've been misinterpreting as planets around stars! [Big flashing Bun]
Dub, Oct 08 2009

       I'm pretty sure I've seen this discussed before on HB but I can't find it now (I hate it when people say that, but in my defence I currently only have internet access through my phone (with its pitifully small screen and rudimentary browser)).   

       On second thoughts, your idea is slightly different to the one I remember. The previously discussed idea was a rotating Dyson sphere with slits/gaps. This has the advantage of being able to communicate with planets that are not exactly co-planar with your sun/satelite system.
xaviergisz, Oct 08 2009

       Also, this is probably not patentable since a patent can only cover things within its jurisdiction (and there is no space jurisdiction yet).
xaviergisz, Oct 08 2009

       Is there something special about 1,3,5,7 that makes it the combination of choice over 1.4, 3.141592 , 7, 13, 16.08 ?   

       Is the ability to send a 'someone was here' to a narrow plane of the surrounds for eternity really so much preferable to blasting away in radio frequencies with a much more informative message for the time one is actually present?
loonquawl, Oct 08 2009

       Your satellites would need to be very large for their effect on blocking a star's light to be evident light-years away. At least moon-size, and likely larger than that. It would also need to be this large to have any visible effect on the gravitational motion of the star, which is one of the big clues we use in determining here to look.
tatterdemalion, Oct 08 2009

       It's generally considered easier just to put a card in a newsagent's window .....
8th of 7, Oct 08 2009

       easy. no problem. use cardboard.
WcW, Oct 08 2009

RayfordSteele, Oct 08 2009

       I don't know if it's feasible with the size difference between a satellite and the sun -- even a moon-size satellite wouldn't block the light reaching other stars; that is to say, if you put your hand up to your brow to block the sun, the reason your hand (very small) can block the light of the sun (very large) is because its distance from you v. the sun's distance is very small, so it appears very large. The distance ratio of any satellite we put up to block sunlight would be gigantically large over a distance of multiple lightyears.   

       Am I right here? Using the same scenario as above, it seems akin to someone standing on the sun holding their hand up to block the light for you. Even a moon-sized satellite would be like a dust mote in front of the sun... I don't think it would make a difference.   

       Also, light and radio waves are very slow for interstellar communication. We have to discover a faster way to transmit over distances before we can truly communicate with anyone else in the cosmos... by the time they receive a message and send one back, it's quite likely our civilization will have perished in the intervening time period.   

       <edit> -- and [tatterdemalion], I was under the impression that the biggest *detectable* effect is the one you mention -- the star "wobble" that happens when large (well, any) gravitational bodies are orbiting relatively closely. (meaning, any orbiting body at any distance causes wobble, but right now, we can only detect the ones with larger planets, close in) </edit>
CaptainClapper, Oct 09 2009

       How will anyone know that this "non-natural" period is non-natural? The arrangement of the planets in our system appears just as non-natural, with the orbital diameters closely following the function: d=n+4, where n=0, 3, 6, 12, etc. It's called Bode's law.
ldischler, Oct 09 2009

       PSYKL here,   

       Good points all, but I think I can address some to clarify. First, it is not necessary for the satellites to be moonsized. The detection of extra solar planets occurs by only slightly dimming the sun. Effectively it is a dust mote in front of a star (Google transit photometry for more). The planets detected so far are huge but because they are so far away they carve out only a fraction of an arc when viewed from earth. Consequently, a smaller satellite closer to the sun would produce the same effect as a large planet further away.   

       However, if there are any physics majors out there, I do wonder how big and close a solar satellite would have to be so you could detect it with the photometry equipment we have now.   

       The object of this idea is that you don't need a civilization much more advanced than our own. Certainly not a class II civilization with its own Dyson sphere made of cardboard or otherwise.   

       As for patenting, I basically meant a method of detection for folks here on Earth, not a method of broadcasting into space. I would hate for first contact to be "Greetings. We are lawyers from Earth; we have come to sue."   

       Also, I agree that there would not be much information in a "blinking" sun but presumably, once you found E.T. you would at least know where to look for a narrow beam broadcast which would carry far more info.   

       You are correct that a 1, 3, 5, 7 period is merely representative, but it seems an "obvious" way to do it instead of semi-log or pi orbital periods or some other way. But maybe we can't assume that suns which dim in prime intervals are obvious to another civilization. On the other hand, I have never heard of anything that in nature that occurs in prime intervals.   

       As for distant communication, you are right. Extra-galactic civilizations would be out of reach for a reply, BUT you could listen in. Who knows, you might detect the Deathstar. Or better yet, search nearby suns for dimming. Although the chances of finding ET go down, if you found one close enough (perhaps under 100 light years away) you could have a "conversation" over the generations.
PSYKL, Oct 09 2009

       mmm pi....   

       a pi orbital would keep scientists guessing for ages at the "natural process" that caused it.
FlyingToaster, Oct 09 2009

       //I have never heard of anything in nature that occurs in prime intervals//   

       1, 3, 5, 7 are four consecutive odd (not prime) numbers (you're missing the 2). (sorry to be pedantic). One interesting feature of consecutive odd numbers is the cumulative sum is a square number (1, 4, 9, 16) which are ubiquitous in nature (ie inverse square law).
xaviergisz, Oct 09 2009

       Pedantic? Nope, that's a good point. Two is prime, but I hate the number two. How can something be both even and prime? I think two is just an irrational number.   

       However, if the satellites are at prime intervals or odd intervals, you should get the same results perhaps supporting the idea that this is a period that would be easily detectable as a non-natural event. (edited because lurch caught me calling two a prime and odd-- he is right, that the statement is wrong.) BUT I am just using this as a for-instance. Any non-natural period would work, as long as its easily recognizable by those without a math Ph.D. such as me and any bone headed extraterrestrials who aren't so good at math.   

       The point is: Is it reasonable for a civilization to use this method for detection and, if so, can we detect it? Please vote fresh if you think so. Otherwise, slap me with a dead fish.
PSYKL, Oct 10 2009

       The planets we have found by photometry have had a dimming factor in the range of 1% - 3%. Jupiter transiting our sun would be into this range - barely - at 1.05%. Now we're going to talk about smaller numbers, so I'm going to use parts per million - Jupiter at 10550 ppm; an Earth transit would only be 83 ppm, and a Lunar transit at 6 ppm. (Taken from a viewpoint outside the solar system, of course.)   

       Now consider your noise sources: our best photometers would have an accuracy of about 10 ppm. How good is ET's? Dunno. How about sunspots? The average photometric dimming of the solar disc at the maximum of the sunspot cycle is around 1000 ppm. A sunspot the size of Earth is really a pretty modest spot. Flares are another source of noise, brightening the solar output rather than dimming it.   

       So, anyway - yes, theoretically, but at a minimum probably about 10 times the diameter of the Earth; or the same size as Earth and make a trip to ET's house, tap it on the shoulder / cranium / appendage, and attract its close attention to *that* *particular* star...   

       <edit - May 15 2013> I'd better put up a qualifier here - it turns out that the photometric variability of stars in the Kepler survey field is only about 19.5 ppm, and the 80 ppm variation caused by the transit of an Earth-sized planet is quite detectable. They were hoping for an average variability closer to 10 ppm, so that an occultation by an earthish planet would be 4 standard deviations over noise; the 19.5 ppm makes it only 2.7 deviations, so it takes more observations to be statistically "sure". But that's techy trivia - occultations *are* detectable, but you do need obscure roughly as much light as a planet would.
lurch, Oct 10 2009


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