Download Chapter 1: A Modern View of the Universe

Chapter 1: A Modern View of the Universe
• 
The Scale of the Universe
•  How big is it?
•  What is our place in it?
• 
The History of the Universe
•  How did we come to be?
•  How do our lifetimes compare?
• 
Spaceship Earth
•  How is Earth moving?
•  How do stars, galaxies move?
Galaxy Song
Composers:
Eric Idle & John Du Prez
Author: Eric Idle
Singer: Eric Idle From the
'Meaning of Life' album
Just remember that you're standing on a planet that's evolving
And revolving at nine hundred miles an hour,
That's orbiting at nineteen miles a second, so it's reckoned,
A sun that is the source of all our power.
The sun and you and me and all the stars that we can see
Are moving at a million miles a day
In an outer spiral arm, at forty thousand miles an hour,
Of the galaxy we call the 'Milky Way'.
Our galaxy itself contains a hundred billion stars.
It's a hundred thousand light years side to side.
It bulges in the middle, sixteen thousand light years thick,
But out by us, it's just three thousand light years wide.
We're thirty thousand light years from galactic central point
We go 'round every two hundred million years,
And our galaxy is only one of millions of billions
In this amazing and expanding universe.
The universe itself keeps on expanding and expanding
In all of the directions it can whiz
As fast as it can go, the speed of light, you know,
Twelve million miles a minute, and that's the fastest speed there is.
So remember, when you're feeling very small and insecure,
How amazingly unlikely is your birth,
And pray that there's intelligent life somewhere up in space,
'Cause there's bugger all down here on Earth.
https://www.youtube.com/watch?v=buqtdpuZxvk
https://www.youtube.com/watch?v=vIy76M-4txo
Misc. Housekeeping Items
•  MasteringAstronomy.com
–  link to text: “The Essential Cosmic Perspective”
•  Online assignments don’t need email submission
–  submission is automatic from textbook webpage
–  All homework due on class day at class time
•  Labs start Monday Sept. 14
–  Download & print PDF files from course webpage
•  Register i>clicker on Sakai, through link to this course:
–  15F-PHYS133010: INTRODUCTION TO ASTRONOMY
Chapter 1: A Modern View of the Universe
• 
The Scale of the Universe
•  How big is it?
•  What is our place in it?
• 
The History of the Universe
•  How did we come to be?
•  How do our lifetimes compare?
• 
Spaceship Earth
•  How is Earth moving?
•  How do stars, galaxies move?
Quick i-clicker quiz on Ch. 1 reading
How long does it take light to
travel from Sun to Earth?
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About a second
About a minute
About 8 minutes
About a day
About a year
© 2015 Pearson
Education, Inc.
How long does it take light to
travel from Sun to Earth?
• 
• 
• 
• 
• 
About a second
About a minute
About 8 minutes
About a day
About a year
© 2015 Pearson
Education, Inc.
How long does it take light to travel
from Alpha Centauri to Earth?
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About a month
About a year
About 4 years
About 1,000 years
About 1,000,000 years
© 2015 Pearson
Education, Inc.
How long does it take light to travel
from Alpha Centauri to Earth?
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• 
• 
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About a month
About a year
About 4 years
About 1,000 years
About 1,000,000 years
© 2015 Pearson
Education, Inc.
Looking back in time
•  Light travels at a finite speed (300,000 km/s).
Destination
Light travel time
Moon
1 second
Sun
8 minutes
Sirius
8 years
Andromeda Galaxy
2.5 million years
•  Thus, we see objects as they were in the past:
The farther away we look in distance, the further
back we look in time.
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Education, Inc.
Definition: Light-Year
•  The distance light can travel in 1 year
•  About 10 trillion kilometers (6 trillion
miles)
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Solar (Star) System
A star and all the material that orbits it,
including its planets and moons
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Galaxy
A great island of stars in space, all held
together by gravity and orbiting a common
center
M31, the great galaxy in
Andromeda
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Education, Inc.
Universe
The sum total of all matter and energy; that is,
everything within and between all galaxies
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Education, Inc.
Example:
This photo shows the Andromeda Galaxy as it looked about 2.5
million years ago.
Question: When will we be able to see what it looks like now?
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Education, Inc.
•  At great distances, we see objects as they
were when the universe was much younger.
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Education, Inc.
Can we see the entire universe?
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Education, Inc.
Thought Question
Why can't we see a galaxy 15 billion light-years away? A. No galaxies exist at such a great distance.
B. Galaxies may exist at that distance, but their light
would be too faint for our telescopes to see.
C.  Looking 15 billion light-years away means looking to
a time before the universe existed.
© 2015 Pearson
Education, Inc.
Thought Question
Why can't we see a galaxy 15 billion light-years away? A. No galaxies exist at such a great distance.
B. Galaxies may exist at that distance, but their light
would be too faint for our telescopes to see.
C.  Looking 15 billion light-years away means looking to
a time before the universe existed.
© 2015 Pearson
Education, Inc.
Our Place in the Universe
•  Key theme: Scale
–  How to comprehend the enourmous scales
–  in distance, time, speed
–  Especially the huge range of scales
•  Requires some key math concepts
–  “Order of magnitude” or “powers of ten”
–  involves fixed factor vs. fixed sum
–  geometric vs. arithmetic growth
What do we mean by scale...
•  scale related to “order of magnitude”
•  can refer to time, distance, or even speed.
•  scales in astronomy are much bigger than
for our lives here on earth
•  and span a wide range
•  so use the Exponents of ten:
10X