Narrator Listen to part of a lecture in an astronomy class. The professo

Professor  Today, we are going to discuss Halley’s Comet. Er...first what do you know about Halley’s Comet?
Student A  Well, Halley’s Comet completed its latest trip around the Earth in 1986. We have all seen that magnificent picture on TV.
Professor  Good. Halley’s Comet is probably the most famous comet. Historians say it was first noted about 2200 years ago. The visit of the bright space object has been observed and recorded every 76 years since then. Can you guess when people on earth will be able to see it again?
Student B  Er...2062! People on earth will not be able to see it again until 2062.
Professor  Terrific!
Student A  Who originally figured this out?
Professor  The comet was named after British scientist Edmund Halley. In the early 1700s, Halley studied records of the appearance of huge balls of fire flying across the sky. He also studied the sky to make his own observations. Halley said the comet orbited the sun just as the planets did. And he said the comet’s trip around the sun took about 76 years.
Student A  Wow, he got it! He is really something!
Professor  When it came, people looked at it by means of various instruments, for instance, through small telescopes they held in their hands. Um...the most recent visit of Halley’s Comet was the first time scientists could study the comet up close. They did this through scientific instruments launched into space.
Student A  How did those scientific instruments work?
Professor  The instruments were carried on five spacecraft that flew near the comet during March 1986. Two Soviet spacecraft flew within 9000 kilometers of the center of the comet on March 6 and 9. Two Japanese spacecraft also observed the comet, but from distances further away. The last and closest look at the comet was made by the spacecraft Giotto.
Student B  Giotto? Was it launched by the European Space Agency?
Professor  Quite right. Giotto flew within about 600 kilometers of the center of Halley’s Comet on March 13. It sent back much valuable information before instruments on the spacecraft were damaged by particles from the comet.
Student A  Er...what were the findings?
Professor  Cameras on the Giotto spacecraft took pictures which show that the dark center of Halley’s Comet is surrounded by a fiery cloud of gas and dust. This cloud is called a coma. Scientists had known for years that such a gassy cloud surrounded the hard icy center of the comet. The bright bursts of gas and dust shoot out of the dark center when the sun heats up the icy center of the comet. The center looks like a sunken volcano.
Student B  Does that mean the center of Halley’s Comet is a large mass of ice covered with dust?
Professor  Actually. Um...more than 30 years ago, an American expert on comets, Dr. Fred Whipple, said he thought comets could be described as dirty snowballs. He said he thought they were huge flying balls of ice in dust. Pictures and information sent to Earth from the spacecraft seem to confirm that he was right. However, scientists were not surprised that this was true. They were surprised however at the size of the comet’s icy center. It is about 15 kilometers long and 8 to 10 kilometers wide. This is almost two times as large as scientists had thought. Also, the comet’s solid center is not smooth and round as experts thought it would be after orbiting the solar system for millions of years. Scientists had been sure the comet was a smooth ball because it follows a smooth path as it orbits the sun. Now they know it looks more like a potato.
Student A  Potato? Such an interesting image...
Professor  Indeed. We have achieved a lot on this subject. Scientists from different countries have shared the information that their spacecraft have gathered about Halley’s Comet. This international cooperation has made it possible to gain a much greater understanding of the comet. They expect to make many more important discoveries and solve some mysteries about the comet as they continue to examine the information gathered from many places here on earth and in space. The scientists hope to continue the international cooperation that made the study of Halley’s Comet such a scientific success.
Student A  Yeah, when many different scientific communities work together, a greater picture is formed.