During a total solar eclipse, the solar corona can be seen by the naked eye.

A corona is an aura of plasma which surrounds the sun and other stars. The Sun's corona extends millions of kilometres into space and is most easily seen during a total solar eclipse. It is also observable with a device called a coronagraph. The word "corona" is a Latin word meaning "crown", from the Ancient Greek κορώνη (korōnē, “garland, wreath”).