Infrared cameras measure heat. They are often used to detect weather patterns like cold fronts, which cause storms, or volcano erruptions that spew gases and ashes into the atmosphere. An example of an infrared camera that is currently in use is the Near Infrared Camera and Multi-Object Spectrometer (NICMOS). It is an instrument currently aboard the Hubble Space Telescope that allows it to make infrared images and spectroscopic observations of stellar phenomena. NICMOS detects light with wavelengths between 0.8 and 2.5 micrometers, which is longer than the human eye can detect. The sensitive arrays, made of the elements mercury, cadmium, and tellurium, which make up the infrared detectors in NICMOS, must operate at very cold temperatures. NICMOS keeps its detectors cold inside a cryogenic dewar (a thermally insulated container much like a thermos bottle) containing frozen nitrogen ice. The dewar keeps the detectors cool for years, much longer than any previous space experiment. NICMOS is Hubble's first cryogenic instrument.