Like other stars, the Sun not only has a corona but also produces a solar wind that pervades the solar system and beyond. The solar wind is a stream or plasma of charged particles that are ejected from the upper atmosphere or corona of the Sun in all directions and at very high speeds. These particles (protons, electrons and heavier ionized atoms) are able to escape the Sun’s gravity because of the enormous thermal pressure produced by the million-degree temperature and high thermal conductivity of the ionized coronal gas, and the associated high kinetic energy of each particle.

There are three types of solar wind: fast, slow, and the massive expulsion of plasmas known as coronal mass ejections. Depending on the amount of surface activity on the Sun, their speeds vary between 300 and 800 kilometres per second—the average being about 400 km/sec (i.e. 895,000 or almost a million miles/hour), taking about seven days to reach the Earth.

© Peter Dawkins