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Unit 1 The Birth and Death of the Sun
Listening Comprehension
About five billion years ago, there was no sun and no planets. The solar system was just a
spinning cloud of gas and dust. Over millions of years, gravity, the force that pulls all things
together, brought the dust cloud together in a ball. As the gas and dust was pressed together,
it became hotter and hotter. Eventually, it became so hot that the dust and gas turned into a
huge ball of fire, and the sun was born.
The sun uses a gas called hydrogen as its fuel. It is extremely hot, over 16 million degrees at
the center of the sun. Because the sun is so hot, the gas is pushed outward by the heat. The
outward push of the gas is exactly as strong as the inward pull of gravity, so the sun is not
getting bigger or smaller. This will be true as long as the sun has hydrogen for fuel. But in
another four or five billion years, the sun will use up most of its hydrogen. Then, the outward
push of the heat will be stronger than the sun’s gravity, and the sun will start to grow. At this
time, Mercury and Venus will be destroyed and Earth will become much too hot for life.
Because the sun will be bigger, it will use its fuel even faster. Eventually, when all the sun’s fuel
is used, its fire will go out and it will start to cool. Gravity will finally pull the sun into a small,
cold ball called a white dwarf. There will be no heat and very little light, and the solar system
will be a cold, dead place.
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Listening Comprehension
About five billion years ago, there was no sun and no planets. The solar system was just a
spinning cloud of gas and dust. Over millions of years, gravity, the force that pulls all things
together, brought the dust cloud together in a ball. As the gas and dust was pressed together,
it became hotter and hotter. Eventually, it became so hot that the dust and gas turned into a
huge ball of fire, and the sun was born.
The sun uses a gas called hydrogen as its fuel. It is extremely hot, over 16 million degrees at
the center of the sun. Because the sun is so hot, the gas is pushed outward by the heat. The
outward push of the gas is exactly as strong as the inward pull of gravity, so the sun is not
getting bigger or smaller. This will be true as long as the sun has hydrogen for fuel. But in
another four or five billion years, the sun will use up most of its hydrogen. Then, the outward
push of the heat will be stronger than the sun’s gravity, and the sun will start to grow. At this
time, Mercury and Venus will be destroyed and Earth will become much too hot for life.
Because the sun will be bigger, it will use its fuel even faster. Eventually, when all the sun’s fuel
is used, its fire will go out and it will start to cool. Gravity will finally pull the sun into a small,
cold ball called a white dwarf. There will be no heat and very little light, and the solar system
will be a cold, dead place.
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