托福听力是考试难点,那么好的听力资料有哪些呢?想必是出国人士比较关心的问题,和新航道托福小编一起来了解托福听力练习之极光,欢迎阅读。
极光
极光（aurora）想必大家都很熟悉，在南北极地区的晴朗夜空中有时会出现，呈现出动态的图案和明亮的颜色，十分壮观。那么极光究竟是如何形成的呢？
极光是太阳风引起的磁层（magnetosphere）扰动的结果。这些扰动改变了磁层等离子体中带电粒子（charged particle）的轨迹，更接近地表的高能量带电粒子会被地球磁场（magnetic field）导向两极地区，从而起到保护地球生物的作用。这些粒子，主要是电子（electron）和质子（proton），沉淀（precipitate）到高层大气（upper atmosphere），即热层（thermosphere）和外逸层（exosphere）中，与氧气和氮气（nitrogen）分子（molecule）发生反应。大气成分的电离和激发（excitation）会发出不同颜色和形状的光。极光的形式也取决于施加给沉淀粒子的加速度（acceleration）。
太阳系中的大多数行星、一些天然卫星、褐矮星，甚至彗星上也能观测到极光。
下面是英文对应的描述，大家可研读积累：
An aurora, also known as the polar lights or aurora polaris (北极星), is a natural light display in Earth's sky, predominantly (主要地) seen in high-latitude (高纬度) regions (around the Arctic (北极) and Antarctic (南极)). Auroras display dynamic (动态的) patterns of brilliant lights that appear as curtains, rays, spirals (螺旋), or dynamic flickers (闪烁) covering the entire sky.
Auroras are the result of disturbances (干扰) in the magnetosphere (磁层) caused by solar wind (太阳风). These disturbances alter (改变) the trajectories (轨迹) of charged (带电的) particles in the magnetospheric plasma (等离子气体). These particles, mainly electrons (电子) and protons (质子), precipitate (沉淀) into the upper atmosphere (thermosphere (热电离层)/exosphere (散逸层)). The resulting ionization (离子化) and excitation (激发) of atmospheric constituents (成分) emit light of varying colour and complexity. The form of the aurora, is also dependent on the amount of acceleration (加速) imparted (给予) to the precipitating particles.
