Declassified NSA document reveals how aliens might contact us

The National Security Agency's (NSA) declassified document is entitled "Communication with Extraterrestrial Intelligence."

The document begins by citing that even the National Academy of Sciences believes that extraterrestrial communication "is no longer something beyond our dreams but a natural event in the history of mankind that will perhaps occur in the lifetime of many of us." Sir Bernard Lovell, a renowned astronomer, has calculated that at least 100 million stars in our galaxy can support organic evolution.

According to Dr. Su-Shu Huang of NASA, our solar system's nearest neighbor, Alpha Centauri, houses planets too young for life to have emerged. Potential candidates would likely be Epsilon Eridani and Tau Ceti, about 11 light-years away from us, compared to Alpha Centauri's 4.3 light-years.

One method of communication that has been listened for by researchers from these candidates involves a signal with a frequency of 1420.405752 megacycles per second, corresponding to a wavelength of 21 centimeters (8.26 inches).

This frequency is the radiation frequency of atomic hydrogen, which "permeates space in great clouds." The frequency can also pass through Earth's atmosphere, and the significance of the frequency would likely be understood by an advanced civilization that can communicate with radio frequencies.

You can download the document to read from the NSA's website.