ASTR 1200 Announcements

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ASTR 1200Announcements
..
Meet in Planetarium next Tuesday First Problem
Set Assigned. Due next Tuesday in
class. Observatory Sessions all now at
830pm Lecture Notes going up on the
websiteSchedule has been updated. Exam dates
set. Text Chapters now posted
..
Website http//casa.colorado.edu/wcash/APS1200/AP
S1200.html
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The Sun
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The Sun
Falls into Disk Stability 99.9 Ended in Sun
(0.1 in Jupiter) Probably the Same Around All
Stars -- Planets are Common
Shoots Planet-Size Bullets into Space
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Most of Mass Forms Ballin Center
A Star Is a Hot Ball of Hydrogen (plus 11 Helium)
One Million Miles
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What Stops the Fall?
Gravity Gets Stronger As Material Gets More Dense
R smaller implies F greater
The smaller it gets, the faster it falls in!
Why doesnt it just become a black hole? Or
worse yet, a point-like singularity of mass?
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Scaling

• Scientists often do scaling do avoid all those
  large numbers.
• For example, the Sun is ABOUT a million times the
  mass of the Earth and a hundred times the size.

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Question

• What is the surface gravity of the Moon in gees?
  R.25Re, M.01Me?
• a).04
• b)4
• c)16
• d).16

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Answer
d
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Temperature
Temperature is a Measure of the Random Kinetic
Energy per Particle
The faster the atoms move, the higher the
temperature.
But were talking about random motion. If they
all move together, then the object moves.
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Thermal Pressure
Thermal Gas Pressure Balances Gravitational
Pressure
Balloon
Every Time An Bounces Off Edge of Balloon It
Keeps It From Collapsing
Thats Pressure
Pressure is Force per Unit Area
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Pressure is Proportional to Temperature
Low Temperature Atoms Move Slowly
High Temperature Atoms Move Fast
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A Star Is Held Up ByThermal Pressure From Below
Gravity
Outer Mass
Individual Atoms Dont Orbit Entire Inside
of Star Like This
They Jostle Each Other But Effect Is The Same
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Temperature Scales

• Fahrenheit
• 0salt water freeze 100human body
• Celsius
• 0pure water freeze 100water boil (sea
  level)
• C(F-32)x5/9
• Kelvin
• 0absolute zero 100 degrees between freeze
  and boil
• KC273
• -273C 0K Absolute Zero

At Absolute Zero Atoms Stop Moving
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Thermal Pressure
P Pressure V Volume n moles R Constant T
Temperature (K)
Ideal Gas Law Chemistry Style
P Pressure V Volume N atoms k Constant T
Temperature (K)
Ideal Gas Law Physics Style
Pressure Is Proportional to Temperature x Density
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Pressure Balance
A Star Always Balances Gravitational Pressure
with Thermal Pressure At Each Point Inside
Thermal Pressure (Jostling)
Gravity
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But We Have a Problem
The Sun is Luminous Radiates Energy Into
Space Luminosity is Power Radiated --
ergs/second
The Energy Comes From Motion of the
Atoms Temperature Drops
What Happens When T Drops?
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Luminosity Effect
When T Drops Thermal Pressure Cant Hold Off
Gravity
The Sun Shrinks -- Radius Drops
Energy is Released as Gas Falls Deeper Into
Gravity Field
Temperature Rises
Note Loss of Energy Results in a) Temperature
Rise b) Radius Decrease
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But Wait A MinuteIsnt the Sun Stable?
The Sun has been remarkably stable for 4 billion
yearsas evidenced by geological records.
This collapse is the process by which the Sun
coalesced. But then it stopped. Why?
The Sun collapsed until a new source of energy
offset the losses to radiation. NUCLEAR FUSION
--- ITS BURNING HYDROGEN As long as it burns H
at this rate, it will be stable.
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Fusion Increases with T
As T in core of Sun increases so does energy
production
Sun shrank steadily, with T rising until, about
10 million years after it started to form, it
reached its current size There is a VERY fast
increase in nuclear energy production above
1,000,000K. At 15,000,000K in the core nuclear
power generated finally balanced the luminosity
from the surface. Thats the equilibrium we are
still in.
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The Nuclear Core
Envelope 1 Million K
core 15x106K
Photosphere 5000K At Surface
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Cosmic Composition

• H hydrogen 89 by number
• He helium 11
• O oxygen 0.1
• C carbon 0.06
• N nitrogen 0.015

Pretty much the composition of the entire
universe. Sun and Jupiter have this
composition Earth does not.
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Fusion vs. Fission
Fusion Atoms unite and release energy
(Fuse) New atom must be no heavier than iron
z26
Fission Heavy atoms split to release energy
Initial atom must be heavier than iron
WWII Nukes were fission bombs made of U and Pu
Sun works on FUSION of H into He
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Proton-Proton Chain
Bottom Line HHHH ? He
1H1 1H1 ? 1H2 e n
1H2 1H1 ? 2He3 g
2He3 2He3 ? 2He4 1H1 1H1
5x106 lt T lt 2x107K
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CNO Cycle
6C12 1H1 ? 7N13 g
7N13 ? 6C13 e n
6C13 1H1 ? 7N14 g
7N14 1H1 ? 8O15 g
8O15 ? 7N15 e n
2x107 lt T lt 108K
7N15 1H1 ? 6C12 2He4
Net 1H1 1H1 1H1 1H1 ? 2He4 2e 4g 2n
hydrogen -gt helium energy
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Triple-a Reaction
2He4 2He4 ? 4Be8 g
T lt 108K
4Be8 2He4 ? 6C12 g
Must be very dense for this to work Be8 decays
back into helium very quickly unless struck by
another He4
Too low density in Big Bang
Net 2He4 2He4 2He4 2He4 ? 6C12 2g
helium -gt carbon energy
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Solar Schematic
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Sunspots
Seen by Ancient Persians
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Groups of Sunspots
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Solar Corona Visible in Eclipse
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The Sun Viewed in X-rays
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X-ray Movie
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X-ray Loops
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Magnetic Structure
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Dynamic Structure
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Solar Turbulence
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Differential Rotation
Rotates in 25 days at Equator 28 days Mid
Latitude 30 days Poles
Rapidly Twists Up