Past Question by GRE Question a Day

Directions: Reading Comprehension - read the following passage to answer the question below.

The ghostly flickering of the Northern Lights is caused by explosions of magnetic energy, say astronomers.

Until now, nobody knew why the aurora sometimes shifted and danced across the sky. And all it took was a fleet of five satellites positioned in the magnetosphere and a team of ground-based observers who caught the beginning of a magnetic storm about 80,000 miles from Earth, or a third of the way to the moon.

The satellites confirmed that the storm was caused by a phenomenon called magnetic reconnection in which solar energy stretches the Earth's magnetic field lines until they reach their limits and snap back into equilibrium. Like an earthquake in the sky, this releases enormous amounts of energy, and charged particles go flying into the atmosphere.

The NASA scientists, who published the work in Science, hope that they can use the new information to better predict geomagnetic storms and protect human assets in space. The storms can knock out satellites, disrupting communication, and endanger astronauts.

Scientists have known that solar particles collide with Earth's atmosphere to produce the glowing celestial displays, known more elegantly as aurora borealis - the "north wind of dawn." But the cause of the fluctuations was in doubt. The so-called solar substorm studied by the researchers took place on February 28. Ninety seconds after the satellites sensed the substorm starting, ground observatories witnessed a Northern Lights display suddenly brighten and dance.
(Adapted from Wired, 2008)

The primary purpose of the passage is to


Describe a newly discovered natural phenomenon.


Explain a natural phenomenon in light of new discoveries.


Consider how the study of a certain natural phenomenon has changed over time.


Portray a natural phenomenon as beautiful but dangerous.


Evaluate the role of NASA scientists in Northern Lights research.

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