 It took more than 30 years to find the 9th planet. In the late 1800s, astronomers suspected there must be another planet beyond Neptune(海王星). Many people searched the dark, distant space hoping to discover “Planet X.” In 1929, a special wide-field camera was installed at the Lowell Observatory in Flagstaff, Arizona. Clyde W. Tombaugh, a young astronomer, began to look for the mysterious planet. Tombaugh would take two photographs of a section of the star-filled sky a few nights apart. Then he would compare the images. He was looking for a moving object. Planets move. Stars do not. They are “fixed” in space. For seven months, Tombaugh patiently inspected a total of 6 million star images. On February 18, 1930, he found a tiny moving planet. The new planet was named Pluto, after the mythological(神话中的) god of the underworld. Pluto appears to be slightly smaller than Earth’s moon. Astronomers think it is a solid mass of ice-covered rock. Some astronomers do not believe that Pluto is truly a planet. Because of its small size, they think it is just another asteroid (小行星). Asteroids are tiny, rock-and-ice objects that orbit(沿轨道飞行) the sun. There are thousands of them in the solar system. Scientists continue to study Pluto to determine whether it really is a planet or a Star. |
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