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Pulling light apart to extract information
A spectrograph operates like a spectroscope except that the small telescope is replaced by a detector that can record the spectrum of the material being studied. The first spectrographs used a photographic camera as a detector.
Anthony Moffat explains what the electromagnetic spectrum is.
Download video: MP4, (3,31 MB), WebM, (2,77 MB), Ogg (1,65 MB) (48 seconds)
ASTROLab/Mont-Mégantic National Park
The electromagnetic spectrum is a way of describing how radiation is emitted from bodies that are warm or hot. This can include everything from gamma rays to X-rays, ultraviolet radiation, optical, infrared and radio. It is just a question of the energy of the radiation – the photons, the elementary wavelets – being propagated. Of course, there are millions of them usually (your eye cannot see them if there are not millions of them) and only difference between them is the energy: the radiation that can be described by the same laws of physics.