Download ISP 205: Visions of the Universe - Department of Physics & Astronomy

Check list
• Visited class web page on
A foot print on the moon
http://physics.uwyo.edu/~mbrother/a1050s11/a1050s11.html?
• Got and READ Syllabus?
• Got Textbook?
• Got Mastering Astronomy account?
• Read the assigned pages for this class?
• Went/Going to Lab?
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© 2010 Pearson Education, Inc.
Chapter 1
Our Place in the Universe
“Space is big. You just won't believe how vastly, hugely,
mind- bogglingly big it is. I mean, you may think it's a long
way down the road to the chemist's, but that's just peanuts
to space.”
Douglas Adams, The Hitchhiker's Guide to the Galaxy
English humorist & science fiction novelist (1952 - 2001)
“Galactic Stress” by David Levine, available for free
online:
http://www.mikebrotherton.com/diamonds/?page_id=41
The opening scene to the movie Contact:
http://www.youtube.com/watch?v=kNAUR7NQCLA
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Chapter 1
Our Place in the Universe
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1.1 Our Modern View of the
Universe
Our goals for learning:
• What is our place in the universe?
• How did we come to be?
• How can we know what the universe was like in the
past?
• Can we see the entire universe?
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What is our place in the universe?
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Star
A large, glowing ball of gas that generates heat
and light through nuclear fusion
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Planet
Mars
Neptune
A moderately large object that orbits a star; it
shines by reflected light. Planets may be rocky,
icy, or gaseous in composition.
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Moon (or Satellite)
An object that orbits
a planet
Ganymede (orbits Jupiter)
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Asteroid
A relatively small and rocky object that
orbits a star
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Comet
A relatively
small and icy
object that
orbits a star
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Pluto
A relatively small
yellow dog from
Disney. “If Pluto
is a dog, then
what’s Goofy?”
Continuing…
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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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Nebula
An interstellar
cloud of gas
and/or dust
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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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Universe
The sum total of all matter and energy;
that is, everything within and between all
galaxies
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How did we come to be?
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How can we know what the universe was
like in the past?
• 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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Example:
We see the
Orion Nebula as
it looked 1500
years ago.
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Example:
This photo shows the Andromeda Galaxy as it looked
about 2 1/2 million years ago.
Question: When will
we be able to see what
it looks like now?
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Light-year
• The distance light can travel in 1 year
• About 10 trillion kilometers (6 trillion
miles)
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• At great distances, we see objects as they were
when the universe was much younger.
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How far is a light-year?
1 light-year = (speed of light)  (1 year)
km   365 days 24 hr 60 min 60 s 

=  300,000





s
1
yr
1
day
1
hr
1
min

 

© 2010 Pearson Education, Inc.
How far is a light-year?
1 light-year = (speed of light)  (1 year)
km   365 days 24 hr 60 min 60 s 

=  300,000




s   1 yr
1 day
1 hr
1 min 

=9,460,000,000,000 km
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Can we see the entire universe?
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Thought Question
Why can’t we see a galaxy 15 billion light-years away?
(Assume the universe is 14 billion years old.)
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Thought Question
Why can’t we see a galaxy 15 billion light-years away?
(Assume the universe is 14 billion years old.)
• Because looking 15 billion light-years
away means looking to a time before the
universe existed.
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Navigating the Universe:
Sizes and Scales
“I don’t pretend to understand the Universe. It’s a great deal
bigger than I am”
- Thomas Carlyle (1795-1881)
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1.2 The Scale of the Universe
Our goals for learning:
•
•
•
•
•
How big is Earth compared to our solar system?
How far away are the stars?
How big is the Milky Way Galaxy?
How big is the universe?
How do our lifetimes compare to the age of the
universe?
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Scale models of the Universe
• Scale Sun as a grapefruit (1:10,000,000,000)
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How big is Earth compared to our solar system?
Let’s reduce the size of the solar system by a factor of
10 billion; the Sun is now the size of a large grapefruit
(14 cm diameter).
How big is Earth on this scale?
A.
B.
C.
D.
an atom
a ball point
a marble
a golf ball
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Let’s reduce the size of the solar system by a factor of
10 billion; the Sun is now the size of a large grapefruit
(14 cm diameter).
How big is Earth on this scale?
A.
B.
C.
D.
an atom
a ball point
a marble
a golf ball
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Where are the planets?
• Mercury = grain of sand, 6 meters
away (19 feet)
• Venus = ball point pen tip, 11
meters (36 feet) away
• Earth = tip of ball point pen, 15
meters (49 feet) away
– Moon = 4 cm away from Earth
• Mars = large grain of sand, 23
meters (75 feet) away
• Jupiter = marble, 78 meters (256
feet!)
• Pluto (R.I.P.) = head of a pin, 1/3
mile away
On this scale, where is the nearest star?
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• On this scale, the nearest
stars would be a triplestar system formed by a
cantaloupe, an apple and
an orange, located a
continent away.
• There is essentially
nothing in between!!
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BIG
NUMBERS
kilo-
Scale of the
Universe
mega- (aka million)
giga- (aka billion)
tera- (aka trillion)
Little
NUMBERS
centimilli34
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1.3 Spaceship Earth
Our goals for learning:
•
•
•
•
How is Earth moving in our solar system?
How is our solar system moving in the Galaxy?
How do galaxies move within the Universe?
How do these translate to motion in our sky?
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How is Earth moving in our solar system?
• Contrary to our perception, we are not “sitting still.”
• We are moving with the Earth in several ways, and at
surprisingly fast speeds…
The Earth rotates
around its axis once
every day.
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Earth orbits the Sun (revolves) once every year:
• at an average distance of 1 AU ≈ 150 million km.
• with Earth’s axis tilted by 23.5º (pointing to Polaris)
• and rotating in the same direction it orbits, counterclockwise as viewed from above the North Pole.
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Our Sun moves randomly relative to the other stars
in the local Solar neighborhood…
• typical relative speeds of more than 70,000 km/hr
• but stars are so far away that we cannot easily notice
their motion
… And orbits the galaxy every 230 million years.
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More detailed study of the Milky Way’s rotation
reveals one of the greatest mysteries in astronomy:
Most of Milky Way’s
light comes from disk
and bulge …
…. but most of the
mass is in its halo
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How do galaxies move within the universe?
Galaxies are carried along with the expansion of the Universe.
But how did Hubble figure out that the universe is expanding?
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Hubble discovered that:
• All galaxies outside our Local Group are
moving away from us.
• The more distant the galaxy, the faster it is
racing away.
Conclusion: We live in an expanding universe.
We will revisit this topic again at the end of the class.
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Are we ever sitting still?
Earth rotates on axis: > 1,000 km/hr
Earth orbits Sun: > 100,000 km/hr
Solar system moves among stars: ~ 70,000 km/hr
Milky Way rotates: ~ 800,000 km/hr
Milky Way moves
in Local Group
Universe
expands
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How has the study of astronomy affected
human history?
• The Copernican revolution showed that Earth was
not the center of the universe (Chapter 3).
• Study of planetary motion led to Newton’s laws of
motion and gravity (Chapter 4).
• Newton’s laws laid the foundation of the industrial
revolution.
• Modern discoveries are continuing to expand our
“cosmic perspective.”
© 2010 Pearson Education, Inc.
For next class meeting, read:
• Chapter 2
Homework:
• Register for MasteringAstronomy (see course website for
instructions)
• complete Introduction Assignments by Wednesday
If I don’t screw up, you can get a copy of each lecture
slides by 9PM the previous day from the course website
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