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  3. Northern lights is the name of a light phenomenon often seen in the northern regions. The lights have been around since Earth fo

Northern lights is the name of a light phenomenon often seen in the northern regions. The lights have been around since Earth fo

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问题     Northern lights is the name of a light phenomenon often seen in the northern regions. The lights have been around since Earth formed an atmosphere—the dinosaurs saw it, early humans saw it and our descendants will see it. The scientific name for the phenomenon is "Aurora Borealis", aurora for short.
    An aurora is a sporadic, generally faint, atmospheric phenomenon usually seen in the night sky from locations at high latitudes. More commonly known as the "northern lights," it may first appear as a faint, milky glow low in the north, too dim for the human eye to detect any color but bright enough to silhouette clouds near the horizon. It may develop into steady greenish arcs or form glaring, swirling curtains of yellow-green light. During the most dramatic displays visible from regions at middle latitudes, such as central Europe and the United States, a crimson glow fills much of the sky. It was this form that inspired European scientists of the 1600s to call the phenomenon aurora borealis, literally "northern dawn," but it also occurs at high southern latitudes, where it is formally called aurora australis, "southern dawn." The same processes are at work in both hemispheres—not just on Earth, but on other planets as well—and today, scientists simply refer to this phenomenon as an aurora. The ghostly forms of an aurora include quiescent patches, veils, and arcs, and rapidly moving rays and curtains.
    Many historical accounts of the northern lights from areas far south of its usual location exist. An early Chinese record describes it as a "red cloud spreading all over the sky." The Roman philosopher Seneca wrote that an aurora in A.D. 37 tricked the emperor into sending troops to aid what he thought was the burning seaport of Ostia, "when the glowing of the sky lasted through a great part of the night, shining dimly like a vast and smoking fire." In 1583, similar "fires in the air" mobilized thousands of French pilgrims, who prayed to avert the wrath of God. On September 15, 1839, an intense aurora dispatched firefighters throughout London.
    What causes the showers of charged particles that create the northern lights? Ultimately, the source lies in the solar wind, a fast-moving stream of particles constantly flowing from the Sun that carries the Sun’s magnetic field out into space. The solar wind, typically moving at 250 miles(400 kilometers)per second, flows past Earth’s magnetic field and molds it into an elongated bubble or cavity, compressing its sunward side and stretching its night side far beyond the Moon’s orbit. Under certain conditions, the solar wind’s magnetic field can merge with Earth’s, creating electrical currents that drive protons and electrons into the polar atmosphere. Powerful events occurring on the Sun can drive enormous changes in the solar wind, increasing both its speed and density and enhancing its effect on Earth.
Auroras that can be seen at middle latitude regions
选项 A、are formed at high latitude regions.
B、used to be known as "northern dawn".
C、appear mainly in the shape of arcs or curtains.
D、are formed at central Europe or the United States.
答案A
解析 根据题干中的middle latitude定位到第2段第4句。原文该句暗示极光仍然是在高纬度的地方形成，但当颜色很浓光度很强烈的时候，极光能照亮半边天空，以至于在中纬度的地方也能看到极光，由此可见，本题应选A。
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