The corona is a huge envelope of gases that form the outer portion of the Sun. It is seen as faint extensions of the Sun’s outer atmosphere during total eclipses and can be observed using a corongraph, a device that is used to create an artificial total solar eclipse.

The shape of the corona varies with the sunspot cycle. At maximum, it is much more even. At minimum, it is seen to be much more irregular with polar tufts, equatorial streamers and plumes being visible.

It has a temperature of between 1 and 2 million K and naturally at that temperature, is a plasma, for example, iron has been identified but with half of its electrons stripped away. It is indeed a very high energy environment. The corona of the Sun is the origin of the solar wind. An estimated 3 million tonnes of material is ejected from the Sun each second.

This material is experienced as the solar wind with ‘gusts’ of up to several hundred km per sec. The Earth is protected from this bombardment of charged particles by its magnetic field which shunts them into the Van Allen Belts. When these overflow at the poles, they create the aurora borealis and aurora australis.

The solar wind appears to be strongest where it flows from coronal holes. These are areas of lower temperature punched through the corona by the powerful magnetic fields of the Sun.

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