Needing to freshen up

Quasars are very compact objects – the word “quasar” and the acronym “QSO” are short for “quasi-stellar radio source” and “Quasi-stellar object” respectively, due to their ‘star-like’ appearance. Quasars were originally discovered with radio telescopes in the 1950s – hence the “r” in “quasar”. It was not until the 1960s that their optical counterparts were faithfully detected and shown to lie at cosmological distances from our own Galaxy: emission features in the optical spectrum of the quasars where systematically shifted towards the red end of the spectrum (“redshifted”) compared to where they ought to lie.