A raw spectrum from ISAAC

A long, narrow slit isolates a small strip of sky. On this image, the slit is vertical, and slightly curved by the optics in ISAAC. The spectrograph then splits the light from the slit into its individual infrared colours, each point of the slit forming a horizontal rainbow. In the lower part, the horizontal fuzzy line is the spectrum of a faint galaxy. The glowing areas on the edge mark the position of the four amplifiers dealing each with a quarter of the detector. These electronic devices are slightly warmer than the rest, causing a minute amount of infrared light registered by the detector.