Astronomy 100 Tuesday, Thursday 2:30 3:45 pm Tom Burbine tburbinemtholyoke.edu www.xanga.comastronom

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Astronomy 100Tuesday, Thursday 230 - 345
pmTom Burbinetburbine_at_mtholyoke.eduwww.xanga.
com/astronomy100
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Exam

• Average 30.3/40 76
• Grades ranged from 0 to 40
• If you guess randomly, a 0 should happen 0.013
  of the time
• Should happen every 7523 tests

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Grade Distribution

• 2 scores between 0 and 10
• 19 scores between 11 and 20
• 47 scores between 21 and 25
• 66 scores between 26 and 30
• 112 scores between 31 and 35
• 65 scores between 36 and 40

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Schedule

• Apr 12  Tue  The Milky Way                        
                       
• Apr 14  Thu      Galaxies                         
                           
• Apr 19  Tue        Life of a Galaxy               
                          
• April 21 Thu No class
• Apr 26  Tue       Dark Matter                     
                             
• Apr 28  Thu      Cosmology and the Big
  Bang                        
• May 3   Tue       Is there life elsewhere in the
  Solar System?    
• May 5   Thu      Is there life elsewhere in the
  Universe?          
• May 10  Tue      Exam 4 (material from April 12
  May 5)
• May 12  Thu      Exam 5 (Comprehensive)
• May 20 Fri Final Exam (Comprehensive) (Optional)

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Exam 5 and Final

• Cumulative
• I will take 10 questions from Exams 1-4
• No question will be exactly the same as ones on
  previous exams
• Most questions will be very similar to those on
  previous exams

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HW and PRS

• You need 20 PRS points to get 10 of your grade
  100
• You need 20 HW points to get 10 of your grade
  100
• We will use the PRS about twice a class
• We will have about 10 more HW points

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Exams

• I am taking the top 4 exams out of 6 exams

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• If your exam average is 55 and your HW/PRS score
  is 100, your average is 64
• If your exam average is 60 and your HW/PRS score
  is 100, your average is 68
• If your exam average is 65 and your HW/PRS score
  is 100, your average is 72
• If your exam average is 70 and your HW/PRS score
  is 100, your average is 76
• If your exam average is 75 and your HW/PRS score
  is 100, your average is 80
• If your exam average is 80 and your HW/PRS score
  is 100, your average is 84
• If your exam average is 85 and your HW/PRS score
  is 100, your average is 88
• If your exam average is 90 and your HW/PRS score
  is 100, your average is 92

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Grading

• I want a class average at the end of the semester
  (top 4 exam scores, PRS, HW) to be at least 80
• If the class average at the end of the semester
  is less than 80
• I will multiply everybodys average by a number
  that equals
• ___________80______________
• class average at end of semester

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Grading

• If the class average is 80 or higher, your grade
  will be based on your top 4 exam scores, PRS, and
  HW

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• A 92.50 - 100
• A- 89.50 92.49
• B 87.50 89.49
• B 82.50 87.49
• B- 79.50 82.49
• C 77.50 79.49
• C 72.50 77.49
• C- 69.50 72.49
• D 67.50 69.49
• D 62.50 67.49
• D- 59.50 62.49
• ? below 59.49

If the class average is 80 or higher, the grade
distribution will be something like this
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OWL assignment (Due Thursday)

• There is be an OWL assignment due on Thursday
  April 14 at 1159 pm.
• There are 15 questions and a perfect score will
  give you 2 homework points.

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Homework Assignment(Due May 3)

• Make up a test question for next test
• 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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What is a Galaxy?

• A Galaxy is a huge collection of stars that are
  bound together by gravity

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Number of Galaxies

• There are thought to be 80 billion galaxies in
  the observable universe

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We live

• We live in the Milky Way Galaxy
• Thought to be 13.6 0.8 billion years old

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Why is it called Milky Way?

• It looked like a flowing ribbon of Milk to the
  Greeks

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Milky Way

• Contains between 200 and 400 billion stars
• Diameter is 100 thousand light years across

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PRS question

• What two elements are the two largest
  constituents of the Milky Way Galaxy?
• A) Helium and Carbon
• B) Helium and Oxygen
• C) Hydrogen and Iron
• D) Carbon and Iron
• E) Hydrogen and Helium

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PRS question

• What two elements are the two largest
  constituents of the Milky Way Galaxy?
• A) Helium and Carbon
• B) Helium and Oxygen
• C) Hydrogen and Iron
• D) Carbon and Iron
• E) Hydrogen and Helium

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Our Galaxy

• There is a disk part
• And Spherical Part Bulge and Halo

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Disk

• The disk includes all of the material (gas, dust,
  stars, and star clusters) which are confined to
  the plane of rotation of the galaxy
• Contains lots of gas and dust and is therefore
  the site of active star formation
• Lots of blue stars (O and B stars)

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Why are O and B stars evidence of active star
formation?

• A) Because they tend to be massive
• B) Because they tend to be older
• C) Because they tend to be younger
• D) Because they tend to be less massive
• E) Because they tend to be cooler

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Why are O and B stars evidence of active star
formation?

• A) Because they tend to be massive
• B) Because they tend to be older
• C) Because they tend to be younger
• D) Because they tend to be less massive
• E) Because they tend to be cooler

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Spiral Arms

• 6 spiral arms

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Spiral Arms

• Cant be fixed patterns of stars
• Stars nearer the center would complete an orbit
  much quicker than stars farther out
• Would cause the arms to wrap up into a tight coil
• We do not see that among spiral galaxies

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Spiral Arms

• Spiral Arms are actively forming new stars
• In spiral arms, see clusters of young, bright,
  blue stars
• In spiral arms, we also see lots of gas and dust
• Between the arms, you see old, red stars

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Bulge

• The bulge is at the center of the galaxy, is a
  flattened spheroid
• This is a high density region where red stars
  predominate, which are very old and about 10
  billion years old
• There is growing evidence for a very massive
  black hole at its center

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Rotation curve
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Rotation curve
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Things you need to remember

• Higher the Force of Gravity
• The faster the velocity of an object rotating
  around a larger object

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Balancing Forces

• Like a spinning hammer thrower
• Faster you spin the hammer
• Stronger the Force needed to keep it from flying
  off

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Rotation Curve

• Rotation curve of galaxy does not fall off with
  distance from center
• The mass of our galaxy is not concentrated in
  center
• More evenly distributed

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Whats the problem

• The stars in the disk do not have enough mass to
  produce this rotation curve
• The unseen mass is thought to be primarily in the
  halo

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Dark Matter

• Most (90) of the Milky Way Galaxy is thought to
  be made of Dark Matter
• Dark Matter is matter where its force of gravity
  can be felt but you cant actually see it

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Possible Dark Matter Candidates

• neutrinos with mass
• undetected brown dwarfs
• white dwarf stars
• black holes
• exotic subatomic particles

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Halo

• The halo is a diffuse spherical region, which
  surrounds the disk.
• It has a low density of old stars mainly in
  globular clusters (these consist of between
  10,000 - 1,000,000 stars).
• The halo is believed to be composed mainly of
  dark matter

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Questions