ESA Science & Technology - Active Regions and Magnetic Loops in the Sun

This image shows the solar disc as observed by SOHO's Extreme ultraviolet Imaging Telescope (EIT) at a wavelength of 171 Å, corresponding to emission lines by highly ionised iron atoms (Fe IX/X). This filter probes material in the lower corona, at a temperature of about 1 million Kelvin.

Spots and loops are clearly visible throughout the solar disc, yielding a lot of information about the Sun's magnetic field: loops correspond to closed magnetic field lines, whereas dark spots correspond to open magnetic field lines, extending into outer space.