Credit : NASA/GSFC
One of the most remarkable discoveries about the Sun’s atmosphere is that it creates a stream of charged particles (mainly protons and electrons) that we call the solar wind. These particles flow from the sun into the solar system at a speed of around 400 kilometers per second. (nearly 1 million miles per hour) The solar wind exists because the gases in the corona are so hot and moving so fast that they cannot be held back by solar gravity. (This wind was actually discovered through its effects on the charged tails of comets; In a way, we can see the tails of comets waving in solar breeze, like windsocks in an airport or curtains fluttering in an open window on the earth.)
Although the material is very, very thinned (that is, extremely low density) in the solar wind, the sun has a huge surface area. Astronomers estimate that the sun loses around 10 million tons of material each year to this wind. While this amount of lost mass appears large to the earth, it is completely negligible to the sun.
Where on the sun does the solar wind come from? In visible photographs, the solar corona appears fairly even and smooth. However, X-ray and extreme ultraviolet images show that the corona has both bright regions, dark regions, loops, & plumes. Large dark areas of the corona that are relatively cool and calm are called coronal holes.
In these regions, the magnetic field lines extend far away from the sun into space and not looping back to the surface. The solar wind comes predominantly from coronal holes in which gas can flow into space unhindered by magnetic fields from the sun. Hot coronal gas, on the other hand, is mainly present where magnetic fields have captured or trapped & concentrated it.
Credit : ucar
On the earth’s surface we are partially protected from the solar wind by our atmosphere and the earth’s magnetic field (see earth as a planet). However, the magnetic field lines enter the earth at the magnetic north & south poles. Charged particles accelerated by the solar wind can follow the field-down into our atmosphere, and when the particles hit air molecules, they make them glow and create beautiful shades of light called the auroras or northern and southern lights.
