Julia M. Riley (nee Hill) a Fellow of Girton College, works at the Cavendish Astrophysics Group, University of Cambridge in the area of radio astronomy. In 1974, along with Fanaroff, she wrote a famous paper classifying radio galaxies into two types based on their morphology (shape). These became known as Fanaroff-Riley type I and II radio galaxies (FRI and FRII). In FRI sources the major part of the radio emission comes from closer to the centre of the source, whereas in FRII sources the major part of the emission comes from hotspots set away from the centre (see active galaxies).
Riley lectures and supervises physics within the Natural Sciences Tripos at the University of Cambridge. She is the daughter of British marine geophysicist Maurice Hill and granddaughter of Nobel-prize winning physiologist Archibald Vivian Hill.