Fraunhofer lines

Fraunhofer lines are absorption lines in the Sun's optical spectrum that were identified and named centuries ago, being the easiest to detect. Some are revealed to be multiple lines by current spectral resolution, totaling thousands, that can include (narrow) emission lines. Only a few Fraunhofer line labels are now commonly used, with some others used occasionally. Each label is a letter with upper-case an lower-case letters indicating different lines, with upper-case letters A through K for the prominent lines. Subscripts are now used in cases where the original letter-designation corresponds to multiple lines now generally discerned. Note that some Fraunhofer lines are actually the result of Earth atmosphere (i.e., telluric lines): at the time of their discovery, this wasn't obvious. Examples:

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.