Caption: A synthetic continuous spectrum (in image representation, NOT flux representation) mimicking the Solar spectrum from range 385--765 nm (i.e., approximately the visible band (fiducial range 0.4--0.7 μm)) with the Fraunhofer lines artificially superimposed. The Fraunhofer lines are the strongest solar absorption lines. There are far more weaker ones. See a real solar spectrum in file Sun file: solar_spectrum_image.html.

Features:

1. The Solar spectrum is the most famous absorption line spectrum.

   The strongest absorption lines (i.e., the Fraunhofer lines) were discovered secondly in 1814 and named with letters by Joseph von Fraunhofer (1787--1826) (see Wikipedia: Fraunhofer lines: Discovery). Nothing about their origin in atoms and molecules was known at that time. The understanding of spectroscopy developed gradually in the course of the 19th century and 20th century (see Wikipedia: History of spectroscopy).

   Note some Fraunhofer lines were discovered firstly by William Hyde Wollaston (1766--1828) in 1802.

2. The Fraunhofer lines are tabulated at Wikipedia: Fraunhofer lines: Naming.

   Representative and famous Fraunhofer lines:

   1. calcium (Ca) K & H lines: 393.366 nm, 396.847 nm in the violet band (fiducial range 0.380--0.450 μm): They are the strongest lines of singly ionized calcium (Ca, Z=20) (AKA Ca II) and arise from its ground state. For a Grotrian diagram of the Ca II atomic line transitions and a table of them, see Moore & Merril (1968, p. 12--13) and file Grotrian diagram file: grotrian_20_01_Ca_II.html.
   2. sodium (Na) D lines: 588.995 nm, 589.592 nm in the yellow band (fiducial range 0.570--0.590 μm): They are the strongest lines of neutral sodium (Na, Z=11) (AKA Na I) and arise from its ground state. They give the characteristic yellow illumination from sodium-vapor lamps. For a Grotrian diagram of the similiar lithium (Li, Z=3) atomic line transitions and a table of Na I atomic line transitions, see Moore & Merril (1968, p. 8--9).

3. Some of the absorption lines in the solar spectrum are telluric lines---they are caused by absorption in the Earth's atmosphere. Telluric lines are traditionally regarded as part of the Fraunhofer lines because they are lines observed by Fraunhofer. Telluric lines are usually removed in modern stellar spectroscopy because they are NOT intrinsic to the nature of stars, and so tell nothing about stars.