This 1991 photograph captures the brief moment of totality when the Sun’s faint corona is most easily observed. It is made up of several photographs from cameras with different settings that were later combined into one image. Credit: Steve Albers, Dennis di Cicco, ad Gary Emerson.
This image appears in the #58: Why is the Sun's Corona So Hot? Technology Through Time article.
The largest, single, challenge for astronauts traveling to Mars will be to overcome exposure to solar storms and radiation.