The solar corona is so hot it can escape even from the powerful gravitational force of
the Sun. It expands into a wind that flows out through space and impacts on the Earth.
Spacecraft data on the solar wind.
Transparency showing solar wind interaction with the Earth.
The solar wind is less dense than the atmosphere in this room by
a factor of 
. In spite of the fact that it is ``almost nothing'',
it serves as a medium by which solar disturbances can affect the Earth.