CN emission in comet LINEAR (C/2000 WM1)

Small part of the UVES spectrum of Comet LINEAR (C/2000 WM1) with an emission band (ultraviolet light at wavelength 390 nm) from CN molecules in the comet's atmosphere. The emission lines are produced by absorption of the solar light by these molecules, followed by re-emission of lines of specific wavelengths. This physical process is known as "resonance-fluorescence" — it is the same process that causes glowing teeth and shirts in a Disco. The upper panel displays the "raw" spectrum; the lower is the "extracted" spectrum, now clearly displaying the individual emission lines.