The solar corona

The halo which appears around the sun during totality and is referred to as the "corona" today was sometimes confused with the remaining section of the sun during annular solar eclipses. It first seems to have been observed during a large solar eclipse in 1567, where it led people to misinterpret the solar eclipse as not being total. Otherwise, the corona was usually associated with the moon: many astronomers believed they could see the moon’s atmosphere in it or an optical phenomenon on the moon’s edge caused by diffraction.

Only very few actually attributed the corona to the sun itself. In his "Beschreibung der Natur-Geschichten des Schweizerlands (external link)" (Zurich, 1707), Johann Jakob Scheuchzer (external link) wrote of the 1706 total eclipse that it had been:

"… clearly visible that the pale (but fiery-red through the telescope) ring seen around the moon during a full eclipse was nothing other than a sheen cast sideways by the sun and carried to us in uninterrupted beams through our air…"

The fact that the corona belonged to the sun was not proved via measurements and established definitively until 1860.

The corona shanges shape from one solar eclipse to the next

Solar eclipse

12 December 1871, 29 August 1886, 21 August 1914

The shape of the corona depends on the sunspot cycle. At the spot's maximum, the corona is virtually symmetrical; the beams are distributed regularly around the sun. A strong flattening with long, distinct beams appears on the sun's equator along with short radial clusters on the poles at the spot’s minimum. The polar beams seem to be linked to the magnetic field that emerges more purely at the spot's minimum.