Transcript Linking Asteroids and Meteorites through Reflectance

Astronomy 100
Tuesday, Thursday 2:30 - 3:45 pm
Tom Burbine
[email protected]
www.xanga.com/astronomy100
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
Grade Distribution
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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
Schedule
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Apr 12 Tue
Apr 14 Thu
Apr 19 Tue
April 21 Thu
Apr 26 Tue
Apr 28 Thu
May 3 Tue
May 5 Thu
May 10 Tue
May 12 Thu
May 20 Fri
The Milky Way
Galaxies
Life of a Galaxy
No class
Dark Matter
Cosmology and the Big Bang
Is there life elsewhere in the Solar System?
Is there life elsewhere in the Universe?
Exam 4 (material from April 12 – May 5)
Exam 5 (Comprehensive)
Final Exam (Comprehensive) (Optional)
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
HW and PRS
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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
Exams
• I am taking the top 4 exams out of 6 exams
• 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%
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 everybody’s average by a number
that equals
___________80%______________
class average at end of semester
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
If the class average is 80% or higher,
A- 89.50 – 92.49 the grade distribution will be
B+ 87.50 – 89.49 something like this
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
OWL assignment (Due Thursday)
• There is be an OWL assignment due on Thursday
April 14 at 11:59 pm.
• There are 15 questions and a perfect score will
give you 2 homework points.
Homework Assignment
(Due May 3)
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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)
What is a Galaxy?
• A Galaxy is a huge collection of stars that are
bound together by gravity
Number of Galaxies
• There are thought to be 80 billion galaxies in the
observable universe
We live
• We live in the Milky Way Galaxy
• Thought to be 13.6 ± 0.8 billion years old
Why is it called Milky Way?
• It looked like a flowing ribbon of Milk to the
Greeks
Milky Way
• Contains between 200 and 400 billion stars
• Diameter is 100 thousand light years across
PRS question
• What two elements are the two largest
constituents of the Milky Way Galaxy?
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A) Helium and Carbon
B) Helium and Oxygen
C) Hydrogen and Iron
D) Carbon and Iron
E) Hydrogen and Helium
PRS question
• What two elements are the two largest
constituents of the Milky Way Galaxy?
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A) Helium and Carbon
B) Helium and Oxygen
C) Hydrogen and Iron
D) Carbon and Iron
E) Hydrogen and Helium
Our Galaxy
• There is a disk part
• And Spherical Part –Bulge and Halo
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)
Why are O and B stars evidence
of active star formation?
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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
Why are O and B stars evidence
of active star formation?
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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
Spiral Arms
• 6 spiral arms
Spiral Arms
• Can’t 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
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
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
Rotation curve
Rotation curve
Things you need to remember
• Higher the Force of Gravity
• The faster the velocity of an object rotating
around a larger object
Balancing Forces
• Like a spinning hammer thrower
• Faster you spin the hammer
• Stronger the Force needed to keep it from flying
off
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
What’s 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
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 can’t actually see it
Possible Dark Matter Candidates
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neutrinos with mass
undetected brown dwarfs
white dwarf stars
black holes
exotic subatomic particles
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
Questions