This image of the corona was taken with the Yohkoh Soft X-Ray Telescope and shows the complex, hot plasmas that make up the corona
This image appears in the #58: Why is the Sun's Corona So Hot? Technology Through Time article.
The most powerful solar flare in the last 500 years occurred on September 2, 1859 and was sighted by two astronomers who happened to be looking at the sun at exactly the right time!