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spectral line
subject			fact

spectral line	has transition
	has equivalent width
	has definition 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.
	has definition 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.).
	has definition 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.
	has definition 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.
	is a kind of spectral feature
spectral feature	has wavelength
	has width
	occurs in
	has species
radiation measurement	has unit radiation unit
number	has value

Kinds of spectral line :

• absorption line (19 kinds, 82 facts) - Dark line in a spectrum, produced when light or other electromagnetic radiation coming from a distant source passes through a gas cloud or similar object closer to the observer. Like emission lines, absorption lines betray the chemical composition and velocity of the material that produces them., Dark line superposed on a continuous spectrum, caused by the absorption of light passing through a gas of lower temperature than the continuum light source.
• emission line (10 kinds, 31 facts) - Bright line superposed on a continuous spectrum. Can be produced in the laboratory by a glowing gas under low pressure., Bright lines produced in a spectrum by a luminous source, such as a star or a bright nebula.
• H alpha (5 facts)
• H beta (5 facts)
• H delta (4 facts)
• H gamma (4 facts)
• hydrogen line (13 kinds, 54 facts) - Set of spectral features associate with neutral hydrogen (H I)
• intercombination line (2 facts) - Spectral line emitted in transitions between two levels with different values of S.
• ionized helium line (9 kinds, 30 facts) - Set of spectral features associate with ionized helium (He II)
• resonance line (2 kinds, 10 facts) - The longest-wavelength line arising from the ground state.
• spectral series line (22 kinds, 82 facts) - A spectral line belonging to a series of lines of a given atom arising from transitions with a common lower energy level.
• U line (3 facts)