Aurorae on Saturn. Hubble Space Telescope coloured ultraviolet image of atmospheric aurorae (bright areas) in Saturn's polar regions. Emissions from neutral hydrogen atoms are blue, whilst those from charged hydrogen ions are red. The aurorae extend about 2000 kilometres (km) above the cloud tops. Aurorae occur when charged particles flowing from the Sun are trapped by Saturn's magnetic field and collide with its atmosphere. These collisions make the gas glow like a fluorescent lamp. Image taken by Hubble's Space Telescope Imaging Spectrograph (STIS) instrument in October 1997 when Saturn was 1.3 billion kilometres from Earth.