In 1938, the International Astronomical Union classified the spectra of Wolf–Rayet stars into types WN and WC, depending on whether the spectrum was dominated by lines of nitrogen or carbon-oxygen respectively.
Međunarodna astronomska unija klasifikovala je 1938. godine sektre Volf-Rajeovih zvezda u tipove WN, WC i WO, u zavisnosti od toga da li su dominantne linije azota, ugljenika i kiseonika redom.