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abstraction > mathematical concept > number > quantity > radiation measurement > spectral feature

spectral feature
subject			fact

spectral feature	has wavelength
	has width
	has definition A feature in the spectra of a celestial object which occurs at a specific wavelength or range of wavelengths
	occurs in
	is a kind of radiation measurement
	has species
radiation measurement	has unit radiation unit
number	has value

Kinds of spectral feature :

• absorption edge (3 kinds, 11 facts) - Sudden rises superposed on the smooth decrease of the curve of the attenuation coefficient, which cause the curve to have a typical sawtooth aspect. They generally occur at the limit of spectral lines.
• set of lines (27 kinds, 80 facts) - A set of absorption or emission lines in the spectra of a celestial object
• spectral line (57 kinds, 205 facts) - Dark lines visible in an absorption spectrum, or bright lines that make up an emission spectrum. They are caused by the transference of an electron in an atom from one energy level to another; strong lines are produced at levels at which such transference occurs easily, weak where it occurs with difficulty. Ionization of certain elements can affect such transferences and cause problems in spectral analysis., Discrete emissions (or absorptions) in frequency, usually formed by atomic transitions. The essential difference between optical line spectra and X-ray spectra is that the former correspond to energy changes in the outer electrons in an atom, and the latter to energy changes in the inner electron orbitals. Gamma rays usually correspond to energy changes in the nucleus. Infrared radiation is produced by high-n transitions of atoms or by the vibration or rotation of molecules. Thermal radio emission is usually produced by still higher-n transitions (the notation 109α corresponds to a transition in a hydrogenic atom between the principal quantum number n = 109 and n' = Δn = n + 1 = 110; similarly, a β-transition indicates Δn = 2. etc.)., Emission or absorption at a discrete wavelength or frequency, caused by atomic or molecular transitions. In the case of atoms, the transitions involve the jump of an electron from one orbit to another; a quantum of light is emitted if the electron jumps toward the nucleus and absorbed if it jumps outward., A line corresponding to an image of the entrance slit of the spectrometer, seen when light is either emitted by or interrupted by a hot rarefied gas such as hydrogen. The pattern is characteristic of the gas and the wavelength at which the features are observed to occur is indicative of the velocity of the object.