SCISAT-1

Fact Sheet 5

Absorption Lines in The Solar Spectrum

The Solar Spectrum

The spectrum above is a medium resolution image of the Sun's spectrum. Notice that the spectrum contains many dark lines. These are called FraunhoferFootnote 1 lines, or more commonly, solar absorption lines.

In Fraunhofer's time it was not realized that the spectral lines were related to specific atomic elements so they were simply catalogued according to their strength, the darkest was designated with the letter A then B followed by C an so on. The legacy of this cataloguing system can be seen in the table below.

The Fraunhofer lines seen in the solar spectrum are a combination of the lines produced as sunlight passes through the outer layers of the Sun's atmosphere plus the lines produced as the sunlight passes through the Earth's atmosphere.

By comparing the spectra of sunlight before and after it has passed through the Earth's atmosphere it is possible to "tease out" which lines arise from atoms and molecules in that part of the Earth's atmosphere through which the sunlight has travelled.

Footnotes

Footnote 1

Joseph Fraunhofer (1787-1826): A talented optician, he was able to produce very good solar spectra which lead to the study of the lines which now bear his name

Return to footnote 1 referrer

Strongest Absorption Lines in the Solar Spectrum
Element Wavelength (nm) Notes
O2 759.4-762.1 this "line" is really a band created by oxygen molecules in the Earth's atmosphere. Letter designation A.
O2 686.7-688.4 this "line" is really a band created by oxygen molecules in the Earth's atmosphere. Letter designation B.
H (hydrogen) 656.28 red (absorption line) known as H-alpha. Letter designation C.
O2 627.6-628.7 this "line" is really a band created by oxygen molecules in the Earth's atmosphere.
Na (sodium) 589.592 sometimes referred to as "sodium D1" (yellow).
Na (sodium) 589.595 sometimes referred to as "sodium D2". D1 and D2 are close together. Sometimes referred to as the "sodium doublet".
He (helium) 587.56 sometimes referred to as "He D3" (yellow).
Fe (iron) 526.95 designated as the E line.
Mg (magnesium) 518.36 sometimes referred to as Mg b1 often appears "blended” with other "b” lines.
Mg (magnesium) 517.27 sometimes referred to as Mg b2 often appears "blended" with other "b" lines.
Fe (iron) 516.89 sometimes referred to as Fe b3 often appears "blended" with other "b" lines.
Fe (iron) 516.74 sometimes referred to as Fe b4 often appears "blended" with other "b" lines.
Mg (magnesium) 516.73 sometimes referred to as Mg b5 often appears "blended" with other "b" lines.
Fe (iron) 495.76 designated as the c line.
H (hydrogen) 486.13 designated as the F line.
Fe (iron) 466.81 designated as the d line.
Fe (iron) 438.35 designated as the e line.
H (hydrogen) 434.05 designated as the f line.
Fe (iron) 430.79 designated as the G line (actually a double line with Ca).
Ca (calcium) 430.77 designated as the G line (actually a double line with Fe).
Ca (calcium) 422.67 designated as the g line.
H (hydrogen) 410.17 designated as the H line.
Ca+ (calcium) 396.84 the "plus sign" indicates that this is singly ionized calcium.
Ca+ (calcium) 393.37 the "plus sign" indicates that this is singly ionized calcium.