Swan bands in bright comet 1995 Q1

The image shows the spectrum was obtained by Alain Smette (Kapteyn Astronomical Institute, Groningen, The Netherlands) with the EMMI instrument at the ESO 3.5-metre New Technology Telescope. The spectral coverage was from about 4900 Angstrom (left) to 6200 Angstrom (right) in the green-yellow region. During the 60 second exposure, the spectrograph slit was oriented along the main tail at position angle ~ 145 degrees. It is easy to see three main band systems of the C2 molecule, known as the Swan bands, with band heads at 5165, 5635 and 6192 Angstroms, respectively. They are seen in most comets that approach the Sun and are named after the English pioneer spectroscopist William Swan (1818 - 1894), who first observed these emissions in hydrocarbons