Definitions

Absorption Lines Gases absorb the light which passes through them at specific lines or frequencies. The lines observed in the spectrum are unique to the molecular or atomic structure of the gas.

Emission Lines In a heated gas or object, light is emitted in specific lines or “frequencies”. The lines observed in the spectrum are unique to the molecular or atomic structure of the gas or object.

Order / Orders See Spectrum Order

Prism A triangular piece of optically polished glass, which breaks light into its constituent colours as it passes through the glass.

Ruling Engine or Engine A precision machine designed to score the fine lines of a spectroscopic grating. They are closely related to the dividing engines used to draw scales on instruments such as surveyor’s transits.

Spectrogram The photographic record of a spectrum.

Spectrograph A spectroscope with a camera either attached or included as part of its design.

Spectroscope A device which includes a prism(s) or spectroscopic grating to separate light into its constituent colours.

Spectroscopic Grating Optically polished metal (“speculum”) or glass ruled with thousands of fine lines, in order to reflect and spread light into its constituent colours; i.e., spectra.

Spectroscopy A branch of physics or chemistry which studies matter using light analyzed with a spectroscope or spectrograph.

Spectrum (pl. Spectra) Colours of the rainbow, produced by a spectroscopic grating or prism.

Spectrum Order Just as rainbows are occasionally seen to have more than one arc, spectra produced with gratings have multiple spectra. The primary or first order is of low magnification or dispersion; the second is more spread-out; the higher-order spectra are dispersed even further. Higher-order spectra reveal greater detail.