Radio image at the 21 centimetre wavelength of neutral hydrogen of spiral galaxy M101, the Pinwheel Galaxy. The picture is colour-coded according to velocity: yellow & red regions are moving away from us, green & blue regions towards us. M101 has a diameter of about 200,000 light years, twice that of our Milky Way galaxy. It is located 20 million light years away. The data for the image was obtained by the Westerbork Synthesis Radio Telescope & processed at Groningen University, Holland.