The Northern Lights

The Sun is stormy（狂暴的）and has its own kind of weather.It is so hot and active that even the Sun ' s

gravity cannot holdits atmosphere in check（控制，支配）!Energy flows away from the Sun toward the Earth

in a stream ofelectrified particles（电粒子）thatmove at speeds around a million miles per hour. These path-

dles are calledplasma（等离子体）, and thestream of plasma coming from the Sun is called the solar wind.

The more active theSun,the stronger the solar wind.

The solar windconstantly streams toward the Earth,but don't worry because a protectivemagnetic field

（磁场）surroundsour planet. The same magnetic field that makes your compass point north alsosteer（引

导）theparticles from the Sun to the north and south poles.The charged particlesbecome trapped in

magnetic beltsaround the Earth.When a large blast of solar wind crashes into the Earth'smagnetic field,the

magnetic field firstgets squeezed and then the magnetic field lines break and reconnect.

The breaking andreconnecting of the magnetic field lines can cause atomic particles（原子粒子）called

electrons（电子）trapped in the belts to fall intothe Earth ' s atmosphere at the poles. As the electrons fall to

the Earth,theycollide with gas molecules（分子）in the atmosphere,creating flashes of light in the sky. Each

atmospheric gasglows a different color. Oxygen and nitrogen glow red and green and nitrogenglows violet-

purple. As thesevarious colors glow and dance in the night sky,they create the Northern Lightsand the

Southern Lights.

Watching auroras isfun and exciting,but normally you can only see them in places far north like Alaska

and Canada.The movement of the aurora across the sky is usually slow enough to easilyfollow with your eyes

but they can alsopulsate（跳动）,flicker,oreven move like waves. During solar maximum,auroras are seen

as far south as Florida,even Mexico!

Auroras often seem to be very close to the ground,but thelowest aurora is still about 100 kilometers

above the ground,adistance much higher than clouds are formed or airplanes can fly.A typicalaurora band

can be thousands ofkilometers long,a few hundred kilometers high,but only a few hundred metersthick.

We hope you are ableto travel to far-north places like the Arctic Circleand see the Northern Lights at

least once duringyour lifetime.We know you will never forget it!The Earth is quitesafe with a magnetic field surrounding it to protect it from the attack by thesolar wind.

A.Right

B.Wrong

C.Not mentioned