Cosmic Clocks: Astronomical Observation from First Principles
How astronomers measure the ages of stars, planets, galaxies and the universe, exploit Doppler shifts, decode the cosmic microwave background, and receive 13.8-billion-year-old light — a first-principles journey through light speed, the distance ladder, spectra and Doppler shifts to stellar, planetary and cosmic ages, then an explicit methodology arc (six indirect-inference patterns, six instrument eras) extending beyond light to neutrinos, gravitational waves, cosmic rays and sample return, closing with satellites and a 2026-08 frontier appendix.