Imagine we have a shade launched in space that can be turned opaque and transparent. We can use it to communicate in binary, and mathematically sound extraterrestrials can pick up the pattern. Of course the shade will be small enough and far enough from the sun, and will block a tiny angle of the sunlight, thus "shading" the message to different star systems as it orbits the sun.

Is this possible, and has it been purposed?

• I'm pretty sure this question has already been asked here, but I can't seem to find it. One thing to keep in mind: you will likely be limited by the speed of sound in the material you are using. – user Feb 18 '17 at 14:00
• @MichaelKjörling The speed of sound? I think you may have misread the question - the structure will flash messages to other star systems by dimming and un-dimming the light from the sun. "Sound" in the second sentence here means "good/competent." – Tharaib Feb 18 '17 at 15:06
• Just from the title I imagined a huge ring of panels which can be turned 90° to either block light or let it pass. As the ring rotates around the sun you see different panels either in "dark"- or "light"-mode, thus encoding the message. After reading the body I changed that to a dyson-sphere, but for communication in arbitray directions. – JFBM Feb 18 '17 at 15:13
• You mean large enough and close enough. Even then, you'd have to have it be a significant fraction of the sun's diameter, or, if distant enough, a multiple. – nzaman Feb 18 '17 at 16:13

We detect planets around other stars by this method - if they pass in front of their star (ie between earth and their star), we detect the drop in brightness.

If the structure was big enough it could therefore certainly cause fluctuations in brightness visible to extraterrestrials - that's not too far from the proposed explanations for the brightness variations in Tabby's Star; the so-called "alien megastructure" star.

How big is big enough? The Wikipedia article I linked to above has a chart that shows masses and radii of planets that have been detected by this method. Planets with a tenth of the radius of earth have been detected successfully.