Principles of transmission

Every pulsar map line was verified against 14 observatories, reducing positional error to under 0.1 arcseconds.

Gold-plated copper resists corrosion for a billion years; the stylus cartridge is rated for 1,000 playbacks at 16⅔ rpm.

Instructions begin with the hydrogen hyperfine transition — the one universal clock any recipient can read.

From 10,000 candidate sounds, 90 minutes were selected: each second tested against the question of translatability.