老托福阅读试题及答案：PASSAGE24.docxVIP

老托福阅读试题及答案：PASSAGE24 为了帮助大家备考托福阅读，提高成绩，下面小编给大家带来老托福阅读真题及答案:passage 24，希望大家喜欢! 老托福阅读试题及答案：PASSAGE24 The spectacular aurora light displays that appear in Earths atmosphere around the north and south magnetic poles were once mysterious phenomena. Now, scientists have data from satellites and ground-based observations from which we know that the aurora brilliance is an immense electrical discharge similar to that occurring in a neon sign. To understand the cause of auroras, first picture the Earth enclosed by its magnetosphere, a huge region created by the Earths magnetic field. Outside the magnetosphere, blasting toward the earth is the solar wind, a swiftly moving plasma of ionized gases with its own magnetic filed. Charged particles in this solar wind speed earthward along the solar winds magnetic lines of force with a spiraling motion. The Earths magnetosphere is a barrier to the solar winds, and forces the charged particles of the solar wind to flow around the magnetosphere itself. But in the polar regions, the magnetic lines of force of the Earth and of the solar wind bunch together. Here many of the solar winds charged particles break through the magnetosphere and enter Earths magnetic field. They then spiral back and forth between the Earths magnetic poles very rapidly. In the polar regions, electrons from the solar wind ionize and excite the atoms and molecules of the upper atmosphere, causing them to emit aurora radiations of visible light. The colors of an aurora depend on the atoms emitting them. The dominant greenish white light comes from low energy excitation of oxygen atoms. During huge magnetic storms oxygen atoms also undergo high energy excitation and emit crimson light. Excited nitrogen atoms contribute bands of color varying from blue to violet. Viewed from outer space, auroras can be seen as dimly glowing belts wrapped around each of the Earths magnetic poles. Each aurora hangs like a curtain of light stretching over the polar regi