Last week, we explained that the planet Mars had passed “opposition.” It passed a point opposite the Sun. This week, we tell about the planet’s surprising motion among the stars.
For thousands of years, people have recognized that planets travel among the stars. The planets generally follow the path taken by the Sun through the sky. The Sun’s path is called the ecliptic. The groups of stars along the ecliptic are called the Zodiac(黄道带).
The motion of the planets can be confusing at times. Everyone knows the Sun rises in the east and sets in the west. But this is caused by the turning motion of the Earth. Planets generally move from west to east.
However, Mars will appear to move backward for about two months this year. This happens because the Earth is overtaking Mars on its way around the Sun. Mars began its backward, or westward, motion on May 11th. It will start moving eastward again on July 19th.
Mars’ apparent motion has been a mystery to astronomers for hundreds of years. Most early theories of tilt solar system argued that the Sun and planets turned around the Earth. But the sudden westward motion of Mars presented problem. Why would Mars move west for two months when it nears “opposition”?
In 1543, a Polish church worker named Nicolas Copernicus published a different theory. His theory said the Earth and planets moved around the Sun in perfectly circular orbits. Copernicus’ theory was simpler. But his Sun-centered system still did not explain the observed motion of Mars very well.
Finally, a German mathematician named Johannes Kepler published a complete theory of the motion of the planets in 1619. He had carefully studied the motion of Mars for many years.
Johannes Kepler discovered that the planets do not move in circular orbits around the Sun. Instead, they travel in flattened orbits called ellipses(椭圆). Mars’ elliptical orbit is the cause of its unusual brightening this year and its apparent large size.
During the next several weeks, you can see for yourself why the mysterious motion of Mars has caused so many people to wonder.
64.From the passage we can learn that _________.
A. the sun and planets generally travel westward
B. Kepler studied the orbit of the planets in 1619
C. Copernicus’ theory well explained the motion of Mars
D. the Earth’s turning motion causes the sun to rise in the east
65.On July 19th Mars _______.
A. will pass the “opposition”                     
B. appears to change its direction again
C. will begin to move westward     
D. appears to change its orbit again
66.Why does Mars appear to be bigger and brighter when it passes “opposition”?
A. It is overtaking the earth                       B. It follows the path of the sun
C. It moves in an elliptical orbit                 D. It travels in a circular orbit.
67.What is the best title for the passage?
A. The Recent Research into Mars          B. The Surprising Motion of Mars
C. The Great Discovery on Mars               D. The Wonderful Mystery of Mars

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