the narrow and elongated region of the magnetosphere of the earth or of another planet that extends in the direction away from the sun.
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Scientific definitions for magnetotail
The elongated extension of the Earth's magnetosphere on the side facing away from the Sun. The magnetotail is shaped by the pressure of the solar wind as it streams around the magnetosphere, compressing it on the side facing the Sun and stretching it on the opposite side into a long, taillike shape trailing far into interplanetary space. See more at magnetosphere.
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