'''ring diagram analysis''' first introduced frank hill used infer speed direction horizontal flows solar surface observing doppler shifts ambient acoustic waves power spectra solar oscillations computed patches solar surface typically thus ring diagram analysis generalization global helioseismology applied local areas sun opposed half sun example sound speed adiabatic index compared within magnetically active inactive quiet sun regions '''time distance helioseismology''' aims measure interpret travel times
Natural science Space science Stellar astrophysics Helioseismology