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abstraction > mathematical concept > number > quantity > radiation measurement > spectral feature > spectral line > absorption line > Fraunhofer line > D line > D2 line

D2 line
subject			fact

D2 line	has wavelength 5890 Å
	has definition Spectral line of neutral sodium.
	is a kind of D line
D line	has species Na I
interstellar line	has width narrow
	has detection procedure narrow absorption lines which don't participate in the periodic Doppler shift of intrinsic absorption lines in a binary star
	has equivalent width depends on the amount of absorbing matter between the source and the observer
	occurs in O stars
Fraunhofer line	has dicovery date 1814
	has discoverer Joseph Fraunhofer
	occurs in Sun
absorption line	has antonym emission line
spectral line	has transition
radiation measurement	has unit radiation unit
number	has value