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UA - PH/AY 101 - Chapters 11 & 12 - Study Guide

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UA - PH/AY 101 - Chapters 11 & 12 - Study Guide

School: University of Alabama - Tuscaloosa
Department: Astronomy
Course: AY 101 - Intro to Astronomy - Jeremy Bailin
Professor: Jeremy Bailin
Term: Spring 2015
Tags:
Name: Chapters 11 & 12
Description: Chapter 11 Our Star • Surface Temp: 5800 Kelvin • Core Temp: 15 Million Kelvin • Composition: 71% hydrogen, 28% Helium, 1% other • The Sun’s energy source was long considered a major mystery? • Is it on fire
Uploaded: 11/04/2015
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background image     Chapter 11 Our Star  •  Surface Temp: 5800 Kelvin  •  Core Temp: 15 Million Kelvin  •  Composition: 71% hydrogen, 28% Helium, 1% other  •  The Sun’s energy source was long considered a major mystery?  •  Is it on fire...NO! Total chemical energy/ energy rate per year ~ 10,000 years -  even if the Sun were one big lump of coal or wood it would only provide energy  for 10,000 years  •  Is it contracting.. NO! Gravitational potential energy/ energy rate per year = 20  million years  •  Is it powered by Nuclear Energy? YES! Nuclear Mass-Energy/energy rate per year  •  Converting a fraction of the Sun’s mass to energy via fusion can power it for 10  billion years  Gravitational Potential Energy  •  In space, an object or gas cloud has more gravitational energy when it is spread  out than when it contracts  •  A contracting cloud converts gravitational potential energy to thermal energy  Fission  •  Big nucleus splits into smaller nuclei + energy (Nuclear power plants)  Fusion  •  Small nuclei stick together to make a bigger nucleus + energy (sun, stars)  Fusion Within The Sun  •  Fusion required very high temperatures (and pressures) to occur at the center of  the Sun  •  How does the Sun get hot?  •  Must understand the role of gravity within the Sun  •  Gravity: inward pull of outer layers of the Sun toward the center, thus heating the  gas at the center of the Sun  •  The weight of upper layers compresses lower layers  •  The upper layers of gas compress and heat up the lower layers of gas → when  central temperature reaches at least 10 million K, fusion  turns on  •  High gas pressure at center of Sun supports the outer layers  
background image     •  Gas at center of Sun has high density and temperature  How does Fusion work?  •  If temperature is too low (protons moving at too low velocities), positively- charged protons will repel each other (both are positive charges)  •  If temperature reaches the crucial barrier of 10 million K, particles move fast  enough to overcome repulsion and stick together  •  If 4 1^H nuclei (protons) stick together, two protons are changed into neutrons →  4^He nucleus + energy   •  The Sun releases energy by fusing four hydrogen nuclei into one helium nucleus   •  Proton-Proton Chain: 1^H fusing into 4^He - Net result  •  IN: 4 protons (1^H nuclei) → OUT: 4^He nucleus, 2 gamma rays → energy, 2  positrons (anti-electrons), 2 neutrinos    •  Four individual protons weight 0.7% more that one 4^He nucleus - this “missing 
mass” has been converted into energy (the two gamma rays) via E=mc^2 
•  The Sun balances gravitational pressure with gas pressure  •  Inward pull of gravity is counterbalanced by the outward force of gas pressure  (gas heated by gamma-rays created by fusion trying to escape)  •  “Hydrostatic or Pressure Equilibrium”  •  Sun neither collapses nor blows apart  How can we really tell what is going on inside the core of the Sun?  •  Neutrinos (nearly-massless neutral particles) created during fusion fly directly  through the Sun  •  Observations of solar neutrons can tell us what’s happening in core  Solar Neutrino Detection  •  Neutrinos are notoriously difficult to detect- perhaps one in a trillion neutrinos  passing through the large detector interacts with matter  •  Would take a layer of lead 1 light year thick to stop an average neutrino  •  Very small fraction of neutrinos can be detected on specially made neutrino  detectors- the predicted number of neutrinos are detected  What is the Structure of the Sun? 
background image     •  Solar Wind: Flow of ions, charged particles (mostly protons and electrons) from 
the Sun’s surface 
•  Corona: Outermost layer of solar atmosphere, Tenuous, low density ~ 1 million K,  hot gas emits optical and X-ray light  •  Chromosphere: Middle layer of solar atmosphere ~10,000-100,000 K, emits UV  light   •  Photosphere: visible surface on Sun, 5800 K  •  Convection Zone: Energy transported upward by rising hot gas bubbles, hot 
bubbles rise → cool off → sink → get reheated → rise, same mechanism that 
moves rock in mantles of terrestrial planets (but much, much hotter and involving  gas)  Granulation  •  Convection (rising hot gas, falling cooler gas) takes energy to surface  •  Hotter gas rises (lighter patches), cooler gas sinks (darker patches)  A Closer Look: Granulation  •  35-minute time lapse image of surface of Sun  •  Convection brings hotter parcels of gas up to the surface of the Sun, where the gas  cools off and sinks back down - leads to mottled appearance of Sun  Radiation Zone  •  Energy transported upward by photons  •  Photons continuously bumped and re-directed by atoms comprising Sun  Core  •  Energy generated by nuclear fusion, 15 million K   •  Pressure, 10^11 atmospheres - keeps Sun from collapsing (10% by mass)  •  Fusion only happens in core (not in other layers)   
 
 
 
 
 
 
 
 

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School: University of Alabama - Tuscaloosa
Department: Astronomy
Course: AY 101 - Intro to Astronomy - Jeremy Bailin
Professor: Jeremy Bailin
Term: Spring 2015
Tags:
Name: Chapters 11 & 12
Description: Chapter 11 Our Star • Surface Temp: 5800 Kelvin • Core Temp: 15 Million Kelvin • Composition: 71% hydrogen, 28% Helium, 1% other • The Sun’s energy source was long considered a major mystery? • Is it on fire
Uploaded: 11/04/2015
9 Pages 33 Views 26 Unlocks
  • Better Grades Guarantee
  • 24/7 Homework help
  • Notes, Study Guides, Flashcards + More!
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