The Heliospheric Imagers on board National Aeronautics and Space Administration (NASA)'s
twin STEREO spacecraft show that coronal mass ejections (CMEs) can be visually complex structures. To
explore this complexity, we created a citizen science project with the U.K. Science Museum, in which
participants were shown pairs of CME images and asked to decide which image in each pair appeared the
most “complicated.” A Bradley‐Terry model was then applied to these data to rank the CMEs by their
“complicatedness,” or “visual complexity.” This complexity ranking revealed that the annual average visual
complexity values follow the solar activity cycle, with a higher level of complexity being observed at the peak
of the cycle. The average complexity of CMEs observed by STEREO‐A was also found to be significantly
higher than those observed by STEREO‐B. Visual complexity was found to be associated with CME size and
brightness, but our results suggest that complexity may be influenced by the scale‐sizes of structure in the
CMEs
