Spectroscopes are simple devices often using a diffraction grating or prism to split visible light into a spectrum. Often used to look at stars or gemstones, the resultant spectrum enables the viewer to determine the makeup of the star or gem in question. Different wavelengths (colours) are absorbed and reflected by different minerals and gases and so because each star or type of gemstone has different physical properties, the spectrum created by each is unique, reflecting which types of gas or mineral it contains.
Small pieces of diffraction grating can be used to recreate the abilities of the spectroscope. Viewing different types of lighting eg; fluorescent tubes, candle flames, coloured bulbs etc give dramatically different spectrums and bands of different colours. These bands can help identify the source gas or filament involved.
Professional spectroscopes now are powered by computer and can accurately identify materials through looking at the light they emit. Photosensors now replace photographic film in recording spectra and data is correlated digitally.
Spectroscopes like the one above are easily broken if dropped and should be inspected after each use to make sure the optics are clean and undamaged.