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What is the solar wind?

The solar windA stream of charged particles, mostly protons and electrons, that escapes into the Sun's outer atmosphere at high speeds and streams out into the solar system. is a stream of charged particles (plasmaPlasma consists of a gas heated to sufficiently high temperatures that the atoms ionize. The properties of the gas are controlled by electromagnetic forces among constituent ions and electrons, which results in a different type of behavior. Plasma is often considered the fourth state of matter (besides solid, liquid, and gas). Most of the matter in the Universe is in the plasma state.) that streams off the Sun at about one million miles per hour (400km/s)! These particles come from the outermost layer of the Sun, called the coronaThe outermost region of the Sun's atmosphere, consisting of thin, ionized gases at a temperature of about 1,000,000 K. It is visible to the naked eye during a solar eclipse.. The corona is a very hot place, about 1.8 million °F (1 million °C). High temperatures cause particles to move faster, so the particles in the corona move very fast. Some of the particles move so fast that the Sun's gravity is not strong enough to hold them down, and so they fly off, becoming part of the solar wind.

The solar wind as seen by the Solar and Heliospheric Observatory (SOHO) spacecraft. Credit: SOHO (ESA & NASA)

The solar wind starts at the corona, and flies out into the Solar System away from the Sun. By the time that the solar wind reaches the Earth, the particles are moving at about 500,000 miles per hour (804,672 km/h). That is about 500 times faster than most supersonic aircrafts! The solar wind strength (the number of charged particles and how fast they are moving) depends on the solar cycle. When the solar wind is particularly strong, it disrupts satellites and electrical grids on Earth. A very strong solar wind can also cause aurorasA display of colored light given off by collisions between charged particles trapped in a planet's magnetic fields and atoms of atmospheric gases near the planet's magnetic poles. Aurora are visible on Earth as the aurora borealis or northern lights and the aurora australis or southern lights., also known as the Northern or Southern Lights.

What is the solar wind?

CLICK TO PLAY MOVIE. Clip from IBEX: Search for the Edge of the Solar System. Credit: NASA/Adler Planetarium.

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Last Updated: 22 NOVEMBER 2010
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