Fraunhofer Lines, the Sun, Elements and Universe

Continuous, Emission and Absorption Spectra Yield Elemental Data

Sep 12, 2009

Understanding the sun, solar systems, and the universe is a constant and intense quest of astronomers. Spectroscopes and Fraunhofer's lines reveal the universal elements.

Visible light reveals a lot to unassisted eyes, however telescopes and spectroscopes expose whole new vistas of awareness that create wonder and stir the imagination.

Three Types of Visible Light Spectra Compared and Contrasted

Issac Newton in 1666 first showed that white light could be divided by prisms into a rainbow of colors — the visible spectrum. Newton also showed prism-separated light passed through a second prism reconstituted white light. Thomas Melvill flamed various chemicals and generated light which showed different spectra when passed through through a prism. In 1802, William Wollaston, an English physicist, first noted distinct dark bands in the solar spectrum.

Fraunhofer Spectral Analyses are Important to Understanding Elements, Atoms, Sun and Universe

Scientists recognize approximately 92 naturally-occurring earthly elements and 72 solar elements.

The sun is 93 million miles (150 million kilometers) away from earth. The sun's core is about 64 % helium and 34 % hydrogen, and the core temperature is 15 million degrees Centigrade (27 million degrees Farenheit). The sun's core is totally gaseous due to the heat which prohibits solid or liquid forms of the elements, but the core is as dense as hard steel with large, concentrated masses of atoms.

Atoms of elements energized by the heat of nuclear fusion reactions can emit light and heat. Beginning in 1814, solar light was analyzed more critically and further by Joseph von Fraunhofer, an optical physicist in Germany, who noted distinct black lines (A through G as major lines, and a total of 576 lines). Fraunhofer proved that the black lines were the absorption spectra — those portions of the spectrum that were missing because they were absorbed. How does this actually happen?

Thermonuclear Solar Reactions, Fusion, Core Density, Electromagnetic Radiation

The sun is an intensely hot mass of hydrogen and helium and associated elements. The core of the sun is hottest, and the sun becomes cooler outward from the core. Intense heat is generated by solar thermonuclear fusion reactions: two hydrogen atoms combine to produce helium.

Fusion generates both heat and light in the sun's core, and all 72 solar elements each emit unique spectral signatures. Solar radiation contains powerful X-rays and visible light which covers the full visible spectrum from 4,000 to 7,000 Angstroms. Light passes from the sun's interior and reaches the corona which is cooler and, there, portions of light are partially absorbed by the various elements.

The characteristic bright emission spectra of earthly elements correspond to the actual, similar elements in the sun. Fraunhofer determined that the dark lines are absorbed, missing regions of the spectrum. Both emission and absorption spectral lines are constant and specific for each element. Further, each element possesses multiple signature spectra. Foucault in 1849 showed that a double yellow flame spectrum was the dark D line of Fraunhofer. Angstrom identified hydrogen's spectrum in 1853, and Bunsen and Kirchhoff followed with systemic flame identification and cataloguing of thousands of spectral lines and the distinct elements they signified. Kirchhoff decoded the meaning of spectral lines, sunlight and Fraunhofer's spectral drawings, and he proved copper, zinc, calcium, iron, magnesium and sodium were present in the sun. In 1869, Lockyer discovered helium in the sun.

Spectroscopes, attached to telescopes, reveal that stars are very elementary, indeed!

Moore, Patrick. 1968. Amateur Astronomy. W.W. Norton & Co., Inc., New York, N.Y. 328 pp

The copyright of the article Fraunhofer Lines, the Sun, Elements and Universe in Scientific Research Methods is owned by Donald Reinhardt. Permission to republish Fraunhofer Lines, the Sun, Elements and Universe in print or online must be granted by the author in writing.