In 1974, radio sources were divided by Fanaroff and Riley into two classes, now known as Fanaroff and Riley Class I (FRI), and Class II (FRII).
En 1974, as fontes de radio foron divididas por Fanaroff e Riley en dúas clases, agora coñecidas como Clase I de Fanaroff e Riley (FRI), e Clase II de Fanaroff e Riley (FRII).