3 June

1997: On 3 June 1997, ESA astronomers announced that they had measured the physical width of a mass of gas swirling into a black hole. This was the first time measurements such as these had been achieved and this data used results gathered over many years by the ESA satellite International Ultraviolet Explorer (IUE).

For many years, theorists had supposed that gravity marshals doomed matter into a flat disk (an 'accretion disk') shaped like a music record, with the hole at the centre. The IUE revealed that, in the galaxy 3C390.3 and at ultraviolet wavelengths, the gaseous mass is indeed rotating around the black hole and is one-fifth of a light-year wide. By this measurement the accretion disk ceased to be a conjecture and became a fact.

1959: On 3 June 1959, scientists used the Moon to relay a transmission of President Eisenhower's message from Millstone Hill Radar Observatory, Westford, United States, to Prince Albert, Canada. Before the serious deployment of communication satellites, the Moon was used to reflect experimental signals from one side of the Earth to another.