It took me a little while to wrap my head around circularly polarized light, or more specifically how this can be done "passively". Wikipedia didn't do much help until I found the article at Polarizer, if any of you were wondering how the new 3D movie technology works. My first question is how the sky looks under circularly polarized lenses. Because polarized sunglasses do such good job of blocking sunlight, I assume there's interference in the atmosphere, at least near the horizon. Looking straight up might be a different story, but for all I know you might have to leave the heliosphere to be certain. I'm sure some of you will be able to chime in on that one. Another way to ask that question is if circular or at least non-linear polarization could exist through natural processes in the universe. Assuming that it does not, then wouldn't that be the signal of choice for any semi-intelligent beings out there? (I say semi-intelligent because they're smart enough to circularly polarize light but dumb enough to broadcast their location to the rest of the cosmos.) Is it possible to do this trick with wavelengths outside of the visible spectrum, like radio or x-ray?