<P> A corona (Latin,' crown') is an aura of plasma that 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, but it is also observable with a coronagraph . The word corona is a Latin word meaning "crown", from the Ancient Greek κορώνη (korōnè, "garland, wreath"). </P> <P> The high temperature of the Sun's corona gives it unusual spectral features, which led some in the 19th century to suggest that it contained a previously unknown element, "coronium". Instead, these spectral features have since been explained by highly ionized iron (Fe - XIV). Bengt Edlén, following the work of Grotrian (1939), first identified the coronal spectral lines in 1940 (observed since 1869) as transitions from low - lying metastable levels of the ground configuration of highly ionised metals (the green Fe - XIV line at 5303 Å, but also the red line Fe - X at 6374 Å). These high stages of ionisation indicate a plasma temperature in excess of 1,000,000 kelvin, much hotter than the surface of the sun . </P>

When can the sun's corona best be seen