Bruce Elsmore was a British radio astronomer who played a key role in the construction and operation of the radio telescopes of the Cambridge radio group from 1948 through to the 5-km radio telescope in the 1970s. With Martin Ryle, he established, using the phenomenal positional accuracy of the 5-km telescope, the radio reference frame, which became fundamental to determining accurate positions on the sky at all wavelengths (Ordish, Bruce Elsemore 1925–2019. Cavendish Laboratory, 2019).