45 Curtains of Light-Mid

Curtains of Light FOCUS Question What are auroras, and how do they form?

光幕焦点问题什么是极光，它们是如何形成的?

NATURAL LIGHT SHOW Near Earth's North and South Poles, people sometimes see a beautiful, natural light show in the sky at night. The light looks like wavy colors hanging on the horizon. This light is not coming from the Moon. What is it, and where does it come from? These lucky sky watchers are seeing auroras (uh-ROAR-uhs) —natural events that occur in Earth's atmosphere. In the Arctic region, these magical light shows are known as the aurora borealis (bore-ee-AL-us). They are nicknamed the northern lights. When seen near the Antarctic, they are called the aurora australis (aw-STRAL-us), or southern lights. Both kinds of auroras are beautiful wavy bands of light They are created by magnetic and electrical reactions high in Earth's atmosphere. Word Wise The famous astronomer Galileo Galilei connected two ancient words to describe the aurora borealis. Aurora was the Roman goddess of the dawn Boreas was the Greek name for the north wind.

在地球的南北极附近，人们有时会在夜间看到美丽的天光秀。 光看起来就像悬挂在地平线上的波浪色。 这个光不是来自月球。 它是什么，又从何而来? 这些幸运的天空观测者看到的是极光——地球大气中发生的自然现象。 在北极地区，这些神奇的灯光表演被称为北极光(borrealis)。 它们被戏称为北极光。 如果在南极附近看到，它们被称为南极光(aw-STRAL-us)，或南极光。 两种极光都是美丽的波浪形光带，它们是由地球大气层高处的磁和电反应产生的。 著名的天文学家伽利略把两个古老的词联系在一起来描述北极光。 奥罗拉是罗马神话中的黎明女神，Boreas是希腊神话中北风的名字。

EARTH'S ATMOSPHERE To understand how auroras form, it helps to know that Earth's atmosphere is made up of five main layers. The layer closest to Earth is the troposphere. Gas molecules are tightly packed together in this layer. Above the troposphere is the stratosphere. The ozone layer is part of the stratosphere. This layer protects Earth by blocking ultraviolet (UV) rays from the Sun. Next comes the mesosphere. This layer is where we see falling stars—meteoroids that burn up as they cross the night sky. Even higher above Earth is the thermosphere. Air in this layer is thin with few gas molecules. This is where auroras form. Beyond the thermosphere is the exosphere. This final layer gradually becomes outer space.

要了解极光是如何形成的，了解地球大气由五个主要层组成是有帮助的。 离地球最近的一层是对流层。 气体分子紧紧地挤在这一层中。 对流层上方是平流层。 臭氧层是平流层的一部分。 这一层通过阻挡来自太阳的紫外线来保护地球。 接下来是中间层。 这一层是我们看到流星的地方——流星穿过夜空时燃烧起来。 离地球更高的是热层。 这一层的空气很薄，气体分子很少。 这就是极光形成的地方。 热层之外是外逸层。 最后一层逐渐成为外层空间。

STORMY SUN How do auroras develop in Earth's thermosphere? Energy from the Sun is one of the key ingredients. The Sun is an enormous ball of burning gases. As it burns, the Sun gives off solar wind—a stream of charged particles that constantly flows into outer space. Solar wind flows away from the Sun in all directions, including toward Earth. During occasional solar storms, the Sun sends out even stronger energy flows into the solar wind. These bursts of energy are called solar flares—giant clouds of gas made up of charged particles To reach Earth, the particles. have to travel 150 million kilometers (93 million mi.). This trip takes from one to five days. Do You Know? Auroras can also occur during the day. We just can't see them because the Sun is too bright.

极光是如何在地球的热层中形成的? 来自太阳的能量是关键成分之一。 太阳是一个巨大的燃烧气体球。 在燃烧的过程中，太阳释放出太阳风——一束不断流入外太空的带电粒子流。 太阳风从太阳向各个方向流动，包括向地球。 在偶尔的太阳风暴中，太阳会向太阳风中释放出更强的能量流。 这些能量爆发被称为太阳耀斑——由带电粒子组成的巨大气体云。 要行驶1.5亿公里(9300万英里)。 这次旅行需要1到5天。 你知道吗?极光也可以在白天出现。 我们看不见它们，因为太阳太亮了。

EARTH'S MAGNETIC SHIELD Most solar flares miss Earth entirely, but some smash right into Earth's magnetic field. Because Earth has an iron core, it acts like a giant bar magnet with lines of force that move from the South Pole to the North Pole. These lines of force create a magnetic field that surrounds Earth. The magnetic field acts like a shield that protects Earth from most of the solar wind. But during strong solar storms, some of the charged particles from the Sun squeeze in between Earth's magnetic lines of force. The particles follow the lines of force, toward the poles where they penetrate Earth's atmosphere.

地球的磁盾大多数太阳耀斑完全与地球擦肩而过，但有些耀斑会直接撞向地球磁场。 因为地球有一个铁核，它就像一个巨大的条形磁铁，有从南极移动到北极的力线。 这些力线形成了环绕地球的磁场。 磁场就像一块盾牌，保护地球不受大部分太阳风的影响。 但在强烈的太阳风暴期间，来自太阳的一些带电粒子挤进了地球的磁力线之间。 粒子沿着力的方向，向两极移动，在那里它们会穿透地球的大气层。

A RAINBOW OF REACTIONS Near the North and South Poles, charged particles from the Sun collide with gas molecules in the thermosphere. The particles bang into each other with such force that a chemical reaction takes place. Each collision produces a tiny burst of light. All those little lights put together form a huge curtain of light—an aurora! The color of the light in an aurora depends upon the kind of gas molecule involved in the reaction. When the solar particles collide with oxygen, green and yellow auroras are created. When the particles collide with nitrogen, we see red, blue, and purple auroras. Some auroras look like motionless rings or bands of light. Others are wavy and dance in beautiful curtains of light.

在南北极附近，来自太阳的带电粒子与热层中的气体分子发生碰撞。 粒子以如此大的力相互撞击，以致发生化学反应。 每次碰撞都会产生微小的光爆发。 所有这些小光放在一起形成了一个巨大的光幕——极光!极光的颜色取决于参与反应的气体分子的种类。 当太阳粒子与氧气碰撞时，绿色和黄色的极光就产生了。 当粒子与氮碰撞时，我们会看到红色、蓝色和紫色的极光。 有些极光看起来像不动的光环或光带。 另一些则是波浪形的，在美丽的光幕中舞蹈。