|solar wind |
A continuous stream of plasma ejected by the Sun, flowing outward from the corona. This plasma, which consists mostly of protons and electrons, has enough energy to escape the Sun's gravitational field at speeds ranging from about 300 to 800 km (186 to 496 mi) per second and averaging 1,610,000 km (1,000,000 mi) per hour, which allows the solar wind to reach Earth in about 3.9 days. The speed and intensity of the solar wind depends on magnetic activity at different regions of the Sun. The solar wind spreads out from the Sun in a pinwheel pattern as a result of the Sun's rotation, pushing back the interstellar medium to the boundary known as the heliopause. The tails of comets, which always extend away from the Sun regardless of the direction of the comet's motion, are a result of the impact of solar wind, which dislodges ice and other particles from the comet's surface. Similar winds flowing from other stars are called stellar winds. See also aurora.