Why do solar physicists like to scan spectral lines?

By analysing the electromagnetic spectrum, scientists are able to learn about the interaction between magnetic fields and the solar gas. A post written by Prof. Francesca Zucarello, from University of Catania (Italy).



Movie by Salvo Guglielmino using data from the CRISP instrument at the Swedish 1-m Solar Telescope on La Palma (Spain). For more details, see Falco et al., 2016, Solar Physics, 291, 1939.


The different layers of the solar atmosphere (photosphere, chromosphere, corona) are characterized by different values of temperature, density, and pressure. The interaction of the magnetic field with the gas present in those layers gives rise to solar features such as pores, sunspots, faculae, and bright points.

Telescopes capture the light emitted by the layers of the solar atmosphere (i.e., the electromagnetic spectrum). A careful analysis of this light allows us to distinguish bright and dark features superposed on the solar spectrum. We call them emission and absorption lines, respectively.

By using instruments capable of acquiring images in different points of the “profile” of such lines, we are able to see how the same portion of the Sun changes with height across the solar atmosphere. The movie shows that effect: the vertical line on the right panel of the plot marks the point of the profile where the corresponding solar image (a large sunspot, left panel) has been acquired.

This kind of analysis is very useful to study how the solar plasma “reacts” to the presence of the magnetic field in the different atmospheric layers. The more accurate the observations are, the more we can learn about how magnetic fields interact with the gas in the solar atmosphere. For this reason, a telescope with a diameter of 4 metres, like the future European Solar Telescope, will be fundamental in order to advance our knowledge of the Sun.


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