Scientists measure the distance to the Moon by bouncing lasers off mirrors placed there by space probes and astronauts.
Radio astronomy began in the 1930s when Karl Jansky, an engineer at Bell Telephone Laboratories, accidentally discovered radio waves coming from the Milky Way. He was investigating sources of interference in transatlantic radio communications, no-one expected this to be the birth of radio astronomy. The finding opened an entirely new window on the universe, one that could peer through clouds, dust and observe phenomena invisible to optical telescopes. The field really took off after World War II when surplus military radar equipment became available to scientists with major discoveries following rapidly from pulsars to quasars, the cosmic microwave background radiation and the detailed structure of galaxies. Today's radio telescopes, from giant single dishes like the 500 metre FAST telescope in China to vast interferometer arrays like the Square Kilometre Array, continue to revolutionise our understanding of the universe.
