Step 01Course 10 · Astrophysics
Nearly everything we know arrives as light, particles, or gravitational waves.
A spectrum carries temperature, composition, density, motion, magnetic field, and redshift. Apparent brightness combines intrinsic luminosity with inverse-square dilution and intervening absorption.
Parallax anchors nearby distances; standard candles and rulers extend the ladder; redshift relates spectra to cosmic expansion only through a model and calibrated rest wavelengths.