1868 - Pierre-Jules-Cesar Janssen and Norman Lockyer discover an unidentified yellow line in solar prominence spectra and suggest it comes from a new element which they name "helium"
1970 - Roger Ulrich , John Leibacher , and Robert Stein deduce from theoretical solar models that the interior of the Sun could act as a resonant acoustic cavity
1975 - Franz-Ludwig Deubner makes the first accurate measurements of the period and horizontal wavelength of the five-minute solar oscillations