Monday reading comp part 2
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Stars By Cindy Grigg |
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1 What
is a star? A star is a giant ball of gases held together by
gravity. It makes heat and light. Different stars produce
different amounts of energy. The amount of energy given off
determines the star's surface temperature and color. Red stars
are cooler, yellow stars like our sun are a little hotter, and
blue stars are the hottest.
2 Stars
are formed in nebulae. A nebula (plural nebulae) is a large cloud
of dust and gas in space. The word nebula comes from the Latin
word for cloud. Most of the gas in a nebula is hydrogen gas. Over
billions of years, the cloud contracts and gets denser and denser
as well as warmer and warmer. As more and more gas is pulled into
the cloud, it begins to spin. As the cloud spins, atoms of
hydrogen gas bump into one another. The faster the gas spins, the
more the atoms bump together, and the temperature of the spinning
cloud gets hotter.
3 When
the temperature reaches ten million degrees Celsius, a chemical
change called nuclear fusion begins to take place. In this
change, two atoms of hydrogen gas combine, or fuse together, to
form an atom of helium gas. This chemical change gives off a
large amount of energy in the form of heat. This is a process
like the opposite of an atomic bomb. Just as splitting atoms
(nuclear fission) gives off a huge amount of energy, the fusion
that takes place in a star also releases huge amounts of energy.
The result is the formation of a new star. The new star gives off
heat and light from the nuclear fusion of hydrogen atoms. New
stars are constantly forming in space.
4 The
star expands and "burns" brightly for a few billion years. Even
though we use the word "burn" with stars, they are not actually
on fire. The heat and light are released by the chemical process
of atoms joining together. This middle stage in the life cycle of
a star is called the main sequence. As the hydrogen is used up,
the star begins to fuse helium and heavier elements. This uses
more of its energy. The star begins to cool off, expand, and
becomes a red giant. Red giants give off lots of light but not
much energy. Smaller stars become white dwarfs as they get older,
and large stars explode as supernovae which burn brightly and
quickly. The material that explodes from a supernova becomes the
gases and dust that creates new stars.
5 If
the helium core survives the explosion and is massive enough, it
may become a black hole. A black hole is a massive star that has
collapsed onto itself. It is very dense. Its gravity is so
strong, not even light can escape. It is invisible. Scientists
have evidence that a black hole is the center of the Milky Way
Galaxy. Its mass has been estimated at over three million times
the mass of our sun!
6 Our
sun, which is about 4.6 billion years old, is a middle-aged star.
It is about half-way through its life cycle. Our sun is also a
medium-sized star. As it ages, the hydrogen will be used up and
more helium will be formed. The helium core will cool and shrink.
Its outer shell will glow more brightly than before, but will
give off less radiant energy. It will grow bigger and bigger,
becoming a red giant that will expand to the orbit of Mars. As it
ages even more, the red giant will cool and contract until it
becomes a white dwarf. All this will happen in another 4-5
billion years!
7 Star
ages are related to their starting masses. In general, stars with
the smallest starting mass last for the longest time, up to about
100 billion years. Stars like our sun that start with an average
mass will last about 10 billion years. Stars with the largest
masses may last only a few billion years.
8 Stars
come in a variety of sizes and colors. A few stars are dwarf
stars that are smaller than Earth. Other stars are supergiants
that are hundreds of times larger than our sun. Our sun is a
medium-sized star with a diameter of about 1,400,000 km. or
865,000 miles. It would take over one hundred Earths to equal the
size of the sun. One of the smallest stars known is Van Maanen's
Star. This dwarf star is about 9,800 km. or 6,100 miles wide. It
is about the same size as the planet Mars. Antares is a
supergiant star with a diameter about 330 times bigger than our
sun!
9 From
our viewpoint here on Earth, some stars appear brighter than
others. Stars are not all the same distance from us. Some are
closer, and some are farther away. The closer a star is to Earth,
the brighter it will appear. Larger stars appear brighter than
smaller stars.
10 If
you have ever looked at a fire, you know that parts of it are
different colors. Different colors are made by different degrees
of temperature. Stars burning at different temperatures also look
different colors. The coolest stars are red. They are also called
M-type stars. Our sun is a G-type star with a surface temperature
from 5,000 to 6,000 degrees Kelvin. The hottest stars are blue,
also known as O-type stars. They have surface temperatures
between 30,000 and 60,000 degrees Kelvin, or 53,500 degrees to
107,500 degrees Fahrenheit!
11 The
star nearest to Earth is our sun. It is the center of our solar
system. Its gravity causes the planets to orbit around it and
holds them in place. The sun rotates on its axis just like the
planets do. It takes about 25 days to rotate. About two-thirds of
the sun is hydrogen and one-third helium. Energy is produced in
the sun's core as the hydrogen is fused into helium because of
heat and pressure. Energy rises to the surface of the sun and
cools as it rises. From the surface, the energy is radiated into
space as heat and light. Without it, we could not
survive.
Copyright © 2014
edHelper
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Gives off heat and
light
Can be red, yellow, or
blue
Is the sun
All of the
above