If you look at the sky one night and see something
moving and shining that you have never seen before, it might be a comet (彗星).
A comet
sometimes looks like a star. Like a planet, a comet has no light of its own. It
shines from the sunlight it reflects (反射). Like the
earth, a comet goes round the sun, but on a much longer path (轨道) than the earth travels.
If a comet isn’t
a star, what is it then?
Some scientists think that a large part of a comet is water frozen into pieces
of ice and mixed with iron and rock dust and perhaps a few big pieces of rock.
When sunshine melts (融化) the ice in the comet, great clouds of gas
go trailing after it. These clouds, together with the dust, form a long
tail.Many people perhaps have seen a comet. However no one knows how many
comets there are. There may be millions of comets, but only a few come close
enough for us to see.
An
Englishman named Edmund Halley, who lived from 1656 to 1742, found out a lot
about the paths that comets take through the sky. Some comets move out of our
sight and never come back. Others keep coming back at regular times. A big
comet that keeps coming back was named after Halley because he was the one who
worked out when it would come back again. Maybe you have ever seen Halley’s
Comets because the last time it came close to the sun and the earth was in the
year 1986. Then people all over the world were outside at night to look at it.
You will probably be able to see Halley’s Comets when it comes near the earth
again.
1.A comet is like ________.
A. sun B.
moon C. sunlight D. the earth
2.A large part of a comet is ______.
A. water and rock
B. water frozen into pieces of ice and mixed with iron
C. ice, iron and rock dust
D. only a few big pieces of rock
3.Maybe many people _______.
A. haven’t seen any
comets B. have seen all comets
C. have seen a comet at daytime D. have seen a
comet
4.Some comets keep coming back ________.
A. at any time B. at noon C. at regular
times D. at daytime
5.Halley’s Comets came back _____.
A. in 1990 B. in
1980 C. in 1986 D. in
1989
