Astronomy 100 Tuesday, Thursday 2:30 - 3:45 pm Tom Burbine [e-mail] www.xanga.com/astronomy100

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Astronomy 100Tuesday, Thursday 230 - 345
pmTom Burbinetburbine_at_mtholyoke.eduwww.xanga.
com/astronomy100
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What we will do today

• Go over exam
• Schedule for rest of class
• The Sun

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Test

• Average score was 27.8 out of 40
• That is a 69.5
• Grades ranged from a 12 to a 40

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Test

• We will go over test

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Exam 2
Exam 1
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Exam 2
Homework score
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Exam 2
PRS score
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Homework Assignment(Due March 31)

• Make up a test question
• Multiple Choice
• A-E possible answers
• 1 point for handing it in
• 1 point for me using it on test
• The question needs to be on material that will be
  on the 3rd exam
• 15 people got extra HW credit for me using their
  question (or inspiring a question)

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I have

• Posted everybodys exam, homework, PRS scores
• If there is a problem, you need to tell me now
• Goal is to get 20 credits with the Homework score
  (10 of grade) and 20 credits with the PRS score
  (10 of grade)
• Then you get perfect score for those parts of
  your grade

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Schedule for Exam 3

• Mar 22 Tue The Suns Energy Source
  
• Mar 24 Thu Stellar Properties
  
• Mar 29 Tue Evolution of Stars
  
• Mar 31 Thu Synthesis of the
  Elements
• Apr 5 Tue Stellar Remnants
  
• Apr 6 Wed Review
• Apr 7 Thu Exam 3

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Schedule for Exam 4

• Apr 12 Tue The Milky Way
  
• Apr 14 Thu Galaxies
  
• Apr 19 Tue Life of a Galaxy
  
• Apr 21 Thu No class
• Apr 26 Tue Dark Matter
  
• Apr 28 Thu Cosmology and the Big
  Bang
• May 3 Tue Is there life elsewhere?
• May 5 Thu Is there life elsewhere?
• May 9 Mon Review
• May 10 Tue Exam 4

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Final

• Is scheduled for
• Friday 5/20 800 AM
• Totman Gym or Trailers GYM
• I know that is last day of finals week
• So

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I will

• Give a Final on the last day of class (May 12)
• And also a different Final on May 20
• I will take the top 4 scores of the 6 exams
• The finals will contain material that people
  tended to get wrong on the earlier tests

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Sun

• Sun is a star

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What is the most abundant element in the Sun?

• A) Helium
• B) Hydrogen
• C) Iron
• D) Lithium
• E) Lead

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What is the most abundant element in the Sun?

• A) Helium
• B) Hydrogen
• C) Iron
• D) Lithium
• E) Lead

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(No Transcript)
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Why does the Sun shine?

• Nuclear fusion the process in which two or more
  smaller nuclei slam together and make a larger
  nucleus

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Is the source of the Suns energy
Figure 15.5
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The nuclei are positively charged
Figure 15.6
Strong Force is the force that holds nuclei
together
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Suns interior

• 15 million Kelvin
• This temperature is hot enough where nuclei can
  fuse together
• Strong Force occurs over short distances and
  allows protons in the nucleus to stay together
• Hydrogen fuses into helium

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Figure 15.7
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Why is energy released when 4 Hydrogen atoms make
one Helium atom?

• A) The mass of 4 Hydrogen atoms is greater than
  the mass of one Helium atom
• B) The gravity of a Helium atom is greater than
  the gravity of 4 Hydrogen atoms
• C) The gravity of a Helium atom is less than the
  gravity of 4 Hydrogen atoms
• D) Electrons are excited during the collision
• E) Neutrons are excited during the collision

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Why is energy released when 4 Hydrogen atoms make
one Helium atom?

• A) The mass of 4 Hydrogen atoms is greater than
  the mass of one Helium atom
• B) The gravity of a Helium atom is greater than
  the gravity of 4 Hydrogen atoms
• C) The gravity of a Helium atom is less than the
  gravity of 4 Hydrogen atoms
• D) Electrons are excited during the collision
• E) Protons are excited during the collision

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Calculation

• 4 protons (Hydrogen atoms) has a mass of
  6.690 x 10-27 kg
• Helium nucleus has mass of 6.643 x 10-27 kg
• This is 99.3 of the original mass
• 0.7 of the mass is turned into energy
• E mc2
• The resulting energy is found as kinetic energy
  of the helium atom, released gamma rays, and
  released neutrinos

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Figure 15.7
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Definitions

• Positron postitively charged electron
  (antimatter)
• Neutrino almost massless particle

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1st Homework question (March 24)(beginning of
class)

• I want you to detail the hydrogen fusion reaction
  (Steps 1 through 3) with words (written by hand)
  and pictures
• What is the solar neutrino problem?
• How was the Homestake Gold Mine used to detect
  neutrinos?

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2nd HW question (due March 24th)(beginning of
class)

• How much longer will it take the Sun to use up
  all its fuel?
• When the Sun uses up its fuel it will start
  expanding, which will be bad for people living on
  Earth
• I want an answer in years
• Show your work

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Things you need to know

• Energy source for sun is four hydrogen atoms
  combining to produce one helium atom
• about 0.7 of the original mass is turned into
  energy during this process
• 10 of the Suns mass is hot enough to undergo
  fusion
• Mass of the Sun 2 x 1030 kg

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And

• Total lifetime (energy available)
• (rate energy/time at which sun emits
  energy)
• rate energy/time at which the Sun emits energy
  is equal to 3.8 x 1026 Watts (Joules/second)

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And

• Time left Lifetime current age
• Current age 5 billion years

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The 2 homework assignments will be due at the
beginning of class

• Or they wont be accepted
• Since I want to go over them next class period
• If you wont be on class on Thursday or will be
  late, email it to me

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Sun is in gravitational equilibrium

• The weight of overlying material is balanced by
  the underlying pressure of hot gas
• This keeps the Suns diameter stable

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Figure 15.2
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How did the Sun form

• Began as a cloud of interstellar gas
• Began to collapse
• Raised the interior temperature higher and higher

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What happened next

• The temperature and density of the center of the
  cloud increased until nuclear fusion could take
  place
• Energy generated from the interior then equaled
  the energy radiated away

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Questions