The solar wind is a stream of charged particles from the Sun. It is made of charged protons, electrons and plasma shot out of the Sun, and creates the heliosphere. The wind is shot out at hypersonic speed, so fast that it can travel the whole length of the Solar System, nearly one light year.

The particles are dangerous to astronauts and spacecraft. The Earth's magnetic field absorbs or soaks up a lot of the solar wind causing the aurora, the Northern lights and Southern lights.

At a distance of more than a few solar radii from the Sun, the solar wind reaches speeds of 250 to 750 kilometers per second and is supersonic.^[2]

A disturbance in the solar wind is called a solar storm. Sometimes it causes a geomagnetic storm. Such a storm in 1989 brought down the Quebec electric power grid^[3] and put the entire province in darkness. The largest recorded geomagnetic storm was in September 1–2, 1859.^[4] If we were to have another as strong as that one it might cause up to 2 trillion dollars damage.

Solar wind also causes the tail of a comet. When the comet is close enough to the sun that the heat evaporates some of the comet's ice, the motion of the solar wind causes the resulting water vapor and space dust to stream away from the comet. Because it is blown by the solar wind, the comet's tail does not trail behind it, but always points directly away from the sun.

The Solar Wind Composition Experiment of the Apollo program studied the atoms in the solar wind.

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