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Part III builds
on our knowledge of the micro-world and of stars to illuminate the
mysteries of the cosmos.
We begin with an exploration
of our universe as it is today. How large is a star? How many stars
are in a galaxy? How many galaxies are there?
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M74 Spiral Galaxy
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How large is the universe?
How small is its smallest part? Where do people fit into all this? We
will discuss what we know, what we don't know, and what we may never know.
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Colliding Galaxies
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ARP 272
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NGC 1300
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Fig 28.3 Left: Colliding Galaxies
450 million light-years away span 150,000 light-years. Right: 70
million light-years away spans 100,000 light-years.
Images by NASA Hubble, ESA |
Next, we turn to cosmology
and explore how the universe, and our understanding of it, has
evolved. Cosmology became a quantitative science in the 20th century
with Einstein's Theory of General Relativity, the discoveries of
Henrietta Leavitt and Edwin Hubble, and the meticulous study of starlight.
Everything astronomers know
about the cosmos comes from observing starlight. It is amazing how
much we can learn from the charming twinkle of stars. From the array
of "colors" in starlight, astronomers obtain a detailed
inventory of the different types of atoms in each star. From changes
in these color patterns, called redshifts, they measure how rapidly
stars, and the universe, are moving.
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Color Plage 11: Color changes of
starlight: (a) stationary star (b) moving star is red-shifted on
left, blue-shifted on right (c) redshift due to expansion of space |
Leavitt became the first
famous female astronomer by discovering the key to measuring the
distances to very remote stars. Hubble used Leavitt's discovery to
demonstrate that there were galaxies beyond our own Milky Way. |
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Our Milky Way Galaxy
Fig 29.2 NASA illustration of what
our own galaxy may look from outside. Milky Way spans 100,000 light-
years and we are 27.000 light-years from the center.
JPL-CalTech-NASA |
Then, Hubble used redshifts,
and distances derived from Leavitt's technique, to discover that
space is expanding. We will find out what is expanding, and what is not.
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One Dimensional Example
of Expanding Space
Figure 33.7 At the bottom is tape
with dimes attached to it. As the tape stretches, the dimes move
further apart, as seen in middle & upper images. Dimes twice as
far apart move away twice as fast because twice as much tape between
them is being stretched. |
Some discoveries are the
result of years of careful preparation and precise observation.
Others are fortuitous accidents, such as the detection of the
afterglow of the Big Bang. This accidental discovery, followed by
decades of meticulous measurement, provides a grand story about the
very early universe.
We will examine the special
and wonderful place Earth occupies in the Goldilocks Zone of this
vast universe.
Next, we turn to the Big
Bang Theory and the beginning of space and time. We will examine the
critical role played by the dark side of our universe: dark matter
and dark energy.
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Galaxies and dark matter (blue)
passed freely,
plasma (red) slowed by collison.
Image by NASA |
Finally, we will explore the
most promising ideas about what came before the beginning. While the
rest of this book is based on well-established science, our
discussion of how it all began will involve intriguing speculation.
To make all this as easy as
possible, physics is translated into English, and equations are
replaced by graphics and heavenly pictures. But the science is not
"dumbed down." This book is like a grand buffet; if you do
not care for anchovies, just skip on to the next delight.
There will be much to think about.
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