Radio image of Tycho's supernova remnant (SNR), recorded at 11cm wavelength by the Cambridge Five Kilometre radio telescope. The dimmest parts are coded blue, with most intense regions coloured purple & white. The radio waves emitted by the SNR are synchrotron radiation produced by high-speed electrons whirling in a magnetic field. The SNR is an expanding shell of gas & dust produced by a supernova explosion that was observed by Danish astronomer Tycho Brahe on 11 November, 1572. It appeared as a bright flashing star, reaching a brightness peak after 4 days & then slowly fading until it became invisible some 15 months later.