Appendix (for reading content...etc)
Read the passage 'Supernovas'. On a piece of paper, take notes on the main points of the reading passage.
Reading time: 3 minutes
Supernovas
In simple terms, a supernova is a star that explodes. During a supernova, a star brightens considerably over a period of about a week and then starts to fade slowly, over a period of a few months or a year or two before it disappears completely.
One kind of supernova is called a Type I supernova. This kind of supernova occurs in a double star system in which one of the stars has become a white dwarf. A double star system, or a binary star, is a pair of stars that are held together by the force of gravity and orbit around each other; a white dwarf is a formerly medium-sized star in the last stages of its life, a star that has run out of fuel and has collapsed into a small, dense star that is smaller than our planet. A Type I supernova occurs only in this very specific situation, when a white dwarf is part of a double star system.
A Type I supernova occurs in a double star system in a situation when a white star's companion star has grown too big. The companion star is always growing, and the white dwarf's companion star will continue to grow in size until its proximity to the white dwarf causes its growth to halt. When the companion star can grow no further, material from the companion star flows from the companion star to the white dwarf. When the white dwarf reaches a certain critical mass, a mass equal to approximately 1.4 times the mass of the Sun, the white dwarf explodes catastrophically in a supernova event.
Only two Type I supernovae have been visible to the naked eye in recorded history, one in 1572 and the other in 1604. Since then, numerous other Type I supernovae have been observed using the telescope, which was invented by Gallileo in 1610.
Main idea of the reading passage:
Major points in the reading passage:
- occurs in double star (white dwarf and companion star)
- occurs when companion grows and matter from it flow to white dwarf (until mass is 1.4 times that of Sun)
- two visible in recorded history (1572 and 1604)
Now listen to the passage. On a piece of paper, take notes on the main points of the listening passage.
[audio|src:'\listening\toefl_begin\CD7-40.mp3?20210805'|wait:185]
Type I supernova, the kind of supernova that you read about in the reading passage, is not the only kind of supernova. The other kind of supernova is called, as you might expect, a Type II supernova.
A Type II supernova occurs when a large star, a single star and not a double star, is in the process of dying. A Type II supernova occurs only in a start that is truly massive, a star that is at least ten times as massive as our Sun.
A supernova occurs in this type of massive star only when it is very old. The core of such a massive star in its very late stages of life becomes progressively hotter and hotter until the core collapses and a whole series of thermonuclear reactions occur, causing a supernova.
Probably the most famous and brightest historical Type II supernova occurred in 1054, near the begriming of the last millennium. It was recorded in China, and Chinese records indicate that it was visible to the naked eye even during daylight for twenty-three days and was visible to the naked eye at night for 653 days, or almost two years. The Chinese also recorded two other supernovae, in 1006 and in 1181, though these were not as bright as the 1054 supernova. From then, it was not until 1987 that another Type II supernova was visible to the naked eye. In 1987, a Type II supernova occurred in a galaxy close to the Milky Way, our galaxy. This was the only supernova that was strong enough and close enough to Earth to be seen from Earth without a telescope in over 400 years, since the two Type I supernovae were observed in 1572 and 1604. The 1987 Supernova was the only Type II supernova to be visible to the naked eye in close to a thousand years.
Main idea of the listening passage:
- Type II kind of supernova
Major points in the listening passage:
- occurs in a massive single star (ten times as big as Sun)
- occurs when massive star becomes hot enough to explode
- four visible in last millennium (1006, 1054, 1181, and 1987)
Now answer the following question:
How does the information in the reading passage contrast with the information in the listening passage?
Sample Answer:
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