Researchers identify useful emission lines in the sun's outer atmosphere

When studying the solar spectrum, researchers often search for specific emission lines: prominent wavelengths emitted by ions as their electrons transition from higher to lower energy levels. Emission spectra of two iron ions, Fe IX and Fe X, are particularly useful for studying the sun's outer atmosphere. However, both of these spectra contain emission lines that can't yet be matched with known electron transitions, limiting the information which can be gathered from them.