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The COSETI Observatory

  • Atmospheric Transmissivity.

    • The so-called “Magic Frequencies” for SETI-type communications may be at wavelengths for which our atmosphere is not transparent. However, the atmosphere is fairly transparent at the C02 laser transition of 10.6 microns.
    • It may be that we will need to deploy space-based optical telescopes to receive transmissions from ETIs.
      • Interstellar absorption at visible wavelengths in the galactic plane is of the order of 4 dB per three thousand light years (equivalent to a one stellar magnitude reduction in brightness). At a range of 20,000 light years, the reduction in intensity is still less than 1,000 times (30 dB), which can be more than made up by the extremely high Effective Isotropic Radiated Powers (EIRPs) of laser transmitters. Such optical transmitters can have EIRPs 100 million times (80 dB) greater than their microwave counterparts.

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