Bright comets are spectacular sights，but they are not often seen by the human eye．
In 1682，the English astronomer Edmund Halley identified and studied the motion of a bright comet．First，he figured out the comet's orbit，or path，around the sun．Then，Halley studied the records of two bright comets observed in 1531 and 1607．He decided that all three were actually the same comet returning to Earth's view about every 76 years．Based on these studies，Halley predicted that the comet would reappear in 1758．His prediction was right，and on December 24，1758，the comet returned． Since then，every 76 years the comet，now called Halley's comet，comes close enough to Earth to be seen either through a telescope or by the naked eye．
The main part of a comet is its nucleus． The nucleus is made up of frozen water，methane（甲烷；沼气），and other gases．Billions of tiny pieces of rock are frozen into the“ice．”As you can see in the diagram on the right，a comet can be very near the sun at one point in its orbit and very far away at another point．As the comet comes closer to the sun，the icy material of its nucleus starts to melt and evaporate．A tail of gas and rock particles forms and may stream millions of kilometers into space．
Solar winds cause the bright，glowing tailto always point away from the sun．A comet's tail is longest when it is nearest the sun．As it moves farther away from the sun，the tail gets smaller and smaller until it finally disappears．
When it appeared in 1910，Halley's comet could be seen clearly in the sky． When the comet appeared in 1985／86，it was farther from the Earth．Light pollution from Earth dimmed some of the comet's light．But it could still be seen without a telescope．
Use the word list to answer questions1，2，and 3．
nucleus orbit telescope
1．A comet's path around the sun is also called its ____ ．
2．The main part of a comet is its ____ ．
3．An instrument that makes far-away objects easier to see is called a ____ ．
4．The first recorded sighting of Halley's comet was in the year ____ ．
5．What causes a comet's tail to form？
a．solar winds b．solar heat c．solar ice
6．After its appearance in 1986，Halley's comet will return again in the year ____ ．
The orbit of Halley's comet is shown in the diagram below．Use the diagram to answer question 7．
7．When will Halley's comet be in the same place as it was in 1948？
___________________________________________________________
参考答案: 1．orbit 2．nucleus 3．telescope 4．1531 5．b 6．2062 7．In 2024．
（from Reading about Science）
吉林白城 韦 佳
