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Fraunhofer lines

(dark lines discovered in the Sun's spectrum two centuries ago)

Fraunhofer lines are absorption lines in the Sun's optical spectrum that were identified centuries ago, being the easiest to detect. Some are revealed to be multiple lines by current spectral resolution, totaling thousands, that include (narrow) emission lines. Their original Fraunhofer line labels are uncommon now, but occasionally seen. Each label is a letter, optionally with a subscript, with upper-case an lower-case letters indicating different lines, with upper-case letters A through K for the prominent lines. Note that some are actually the result of Earth atmosphere, which affected all solar observation at the time of their discovery. Examples:

A759.4terrestrial oxygen
B686.7terrestrial oxygen
C656.3hydrogen (H-alpha)
D1589.6neutral sodium (Na I)
D2589.0neutral sodium
E527.0neutral iron (Fe I)
F486.1hydrogen (Hβ)
G430.7blended line from CH, iron, calcium, and others
H396.8ionized calcium (CA II)
K393.4ionized calcium

One term still seen occasionally is Fraunhofer's G band (or just G band) for the Fraunhofer G line, which was actually multiple lines of nearly the same wavelength in the vicinity of 429.5-431.5 nm. The term K-line is also still seen but is ambiguous because other incompatible uses of the term are now more common.

Further reading:

Referenced by pages:
G band
sodium (Na)
spectral line designation
Wilson-Bappu effect