These observations of an active region were taken with the SOUP tunable filter in the center of the H-alpha line at the Swedish 1-m Solar Telescope on October 4, 2005. The center of the H-alpha line takes us to around 2000 km above the surface of the Sun (to a layer called chromosphere) where we see a very different scenario than in the surface of the Sun. Below, in the surface, solar activity produces dark sunspots, bright plage, bundles of bright points, etc. At this height, we see the chromospheric counterpart of that photospheric activity.
In the chromosphere the density of the plasma has dropped so much that the plasma does not dominate the movements of the magnetic field anymore, now it is the magnetic field that controls the dynamics of the plasma. Due to the low density, magnetic field lines fan out (they are not constrained anymore and feel free to expand horizontally). When they fan out, they form a canopy that covers almost everything. One can literally see the magnetic field lines coming out of the sunspots and connecting opposite polarities in the Sun. We "see" them because plasma gets trapped in them and trace their existence. This image shows us the beautiful interconnection of field lines between the different centres of activity which have opposite magnetic polarities.
Image credit: Luc Rouppe van der Voort, Michiel van Noort (ITA, University of Oslo)
Text credit: Ada Ortiz (ITA, University of Oslo)
Sunspot observed in Ca II K spectral line
The same sunspot in three different layers
A sunspot observed in multiple spectral lines
The amazing chromosphere above an active region (1/3)
The amazing chromosphere above an active region (2/3)
The amazing chromosphere above an active region (3/3)