There Are Colors Missing From The Sun - And We Still Can't Fully Explain Why

The Sun, our nearest star, emits a spectrum of light, but a detailed analysis reveals some surprising gaps in its rainbow of colors. While scientists have successfully linked most of the dark Fraunhofer lines to elements in the Sun's atmosphere that absorb light at specific wavelengths, some lines remain stubbornly unidentified.

Decades of high-resolution solar spectroscopy have been dedicated to unraveling these mysteries. The Sun, however, holds onto its secrets tightly.

One of the best visualizations ever produced of the spectrum of light from our glorious Sun reveals some mysterious holes in its array of colors.

The solar spectrum, compiled from observations at the US National Solar Observatory on Kitt Peak in the 1980s, holds several noteworthy features. Despite the Sun's rays appearing colorless, the spectrum's brightest point lies in the yellow-green wavelengths. Another key feature is the presence of dark patches, known as Fraunhofer lines, documented by Josef von Fraunhofer in 1814. These absorption lines, also seen in the spectra of other stars and galaxies, result from atoms and molecules in the solar atmosphere absorbing photons.

Each element has a unique pattern of absorption lines, creating a spectral "fingerprint." This allows scientists to determine a star's composition, although overlapping fingerprints can complicate the process. The analysis of Fraunhofer lines has revealed that the Sun, primarily composed of hydrogen and helium, also contains elements like oxygen, sodium, calcium, and even trace amounts of mercury.

The elemental composition of stars is more than a matter of curiosity. In the early universe, hydrogen and helium were the dominant elements. Stars forge heavier elements in their cores, scattering them into space upon their death through violent explosions. Subsequent generations of stars incorporate these materials, and the abundance of heavier elements serves as a tool for estimating a star's age.

The Sun, being our closest star, provides the most detailed spectral data. Yet, hundreds of absorption features remain unmatched or inconsistent with synthetic spectra – computer-generated spectra based on the Sun's known properties. A 2017 paper highlights several reasons for these discrepancies.

One major factor is the incompleteness of current atomic and molecular line databases. Determining the spectral fingerprint of an element often requires extensive testing, and some elements, like those in the iron group, are particularly complex. The Sun's dynamic atmosphere, characterized by convection and fluctuating magnetic fields, also complicates the identification of absorption features.

Consequently, mystery lines persist in the solar spectrum, defying identification with known atomic or molecular absorption. It's remarkable that even after centuries of study, our closest star still presents unsolved mysteries that are more complex than they initially appear.

Progress is being made through improved instruments, expanding spectral line databases, and refined atmospheric models of the Sun. Each discrepancy between real and synthetic spectra provides valuable clues for refining these models. While the study of the Sun may never be truly finished, each step brings us closer to understanding its complexities.