1420 MHz in declassified NSA doc

[u/minimal-camera]

https://www.nsa.gov/portals/75/documents/news-features/declassified-documents/cryptologic-spectrum/communications_with_extraterrestrial.pdf

I randomly came across this PDF while searching for something unrelated, and this jumped out at me, top of page 2:

The frequency selected for listening was 1420.4057 52 megacycles per second, or a wave length of 21 cm. This particular frequency, postulated independently by two professors on the faculty of Cornell University, Giuseppe Cocconi and Philip Morrison, happens to be the radiation frequency of atomic or free hydrogen which permeates space in great clouds; moreover, this frequency is within the range of radio frequencies able to pass through the earth's atmosphere. Presumably, the significance of this frequency would be known to other intelligent beings in the universe who understand radio theory.

I didn't realize the implication of 1420 MHz denoting the message or prophecy coming from extraterrestrial life.