Corona
http://lasco-www.nrl.navy.mil/
The Solar corona is the outermost layer of the solar atmosphere, characterized by low densities ( cm-3) and high temperatures (> 106 K) that extends to several solar radii. The shape of the corona is different at solar maximum and solar minimum. The heating of the corona has been a long-standing mystery. Image shown is from the LASCO experiment on SOHO.