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P. 5
Unit 1 The Birth and Death of the Sun
Reading 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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Reading 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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