Astronomy 1 – Fall 2014
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Lecture 1; October 2, 2014
Astronomy 1
• Lectures:
– T/R 2:00-3:15
• Instructor office hours:
– Prof. Crystal Martin
• T 3:15-:400 & W 9:15-10:30; Broida 2015D
• Email: starprof@physics.ucsb.edu
– Email to other addresses will be directed to junk folder and
never read.
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Astronomy 1
• Textbook:
– Universe 10th edition R.A. Freedman, Geller, and
Kaufmann
• I will use iclickers
– Available from bookstore
– Buy your iClickers and register them online before Tuesday’s class
– iClickers are used to assign points for class participation
• You just need to reply: it does not matter if you give the right
answer!
• Website: web.physics.ucsb.edu/~astro1/fall2014
• Lecture notes and homework assignments can be
found on the website.
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Astronomy 1
• Study Tips
– It is recommended to read the material before lecture.
• Reading assignments are listed on the course website.
• You are responsible for assigned reading even if I don’t cover
that material in class.
– Homework problems are assigned each lecture and due on
the following Monday.
• Homework assignments are listed on the course website.
• Do all the review questions for each chapter that we cover.
– Bring your questions to Discussion Section and/or Office Hours.
– Only a subset of the homework problems can be graded each week.
– Review the solutions to all the problems.
– Focus on understanding the physical concepts and
critical thinking rather than rote memorization.
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Astronomy 1
• Teaching Assistants and office hours (in PSR):
– Stephanie Ho – see website
– Owen Colegrove – see website
• Discussion Sections:
–
–
–
–
–
–
–
F 9-9:50am (BSIF 1217, Colegrove)
W 1-1:50pm (GIRV 1112, Ho)
W 4-4:50pm (BSIF 1217, Colegrove)
W 5-5:50pm (BSIF 1217, Ho)
W 6-6:50on (BSIF 1217, Colegrove)
M 4-4:50pm (BSIF 1217, Ho)
Honors W 8-9:15am
• Bring a calculator to the section.
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Astronomy 1
• Grades as in Table. If class
performs badly I will
renormalize the grades
• Grading:
– 25% Homework and Discussion
Section Participation
– 5% Class participation
– 15% Midterm-1 (October 28,
2014; 2-3:15pm)
– 15% Midterm-2 (December 2,
2014; 2-3:15pm)
– 40% Final exam (December 16,
2011; 4-7PM)
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A+
95%
C+
60%
A
90%
C
55%
A-
85%
C-
50%
B+
80%
D
40%
B
75%
F
<40%
B-
70%
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Astronomy 1
• Read polices listed on course syllabus.
• Please note that there will be no early or make-up exams.
– You can miss up to 2 lectures and1 discussion section without penalty.
• Turn in homework by 6pm Monday. Use the drop box.
– No late homework will be accepted.
– I will drop your lowest homework score.
• I expect the highest level of academic integrity from you.
– First offense earns you a zero for the course.
– Example: Surf’s up. You send your iclicker to lecture with your
roommate. What grade do you get for the class? Your roommate?
• What you might think of as “joking around” can be a serious
problem if it inhibits others from participation.
– This includes, but it is not limited to, comments that question the ability
of others to learn the material.
– This behavior is prohibited by the UCSB Code for Student Conduct in
which it is considered a form of hazing
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Hazing and Harassment:
where to report
•
•
•
•
Professor in charge (me)
Any department faculty
Faculty undergraduate advisor
Director of Judicial Affairs, Stephan Franklin
(893 4569, franklin-s@sa.ucsb.edu)
• UCSB office of equal opportunity and sexual
harassment/Title IX compliance (893-5410,
kristen.gibson@oeosh.ucsb.edu)
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Astronomy 1
• Waitlist:
– http://registrar.sa.ucsb.edu/waitlist.aspx
– Attend lecture and discussion session or you will be
dropped from the waitlist.
– Adds made at end of second week.
• Now, let’s get on with Astronomy 1 which is
all about understanding our place in the
Universe.
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Astronomy 1 – Three goals
• Understand the scientific method – what is science?
What is NOT science
• Improve your understanding of the universe – what
are planets, stars, and galaxies?
• Learn to understand the language of science – words
and numbers.
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Goal 1 - What is science?
Example. Is astrology science?
Let’s discuss
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Methodological introduction
• Demarcation: what is science?
• Falsification: how do you test scientific
theories?
– Measurements and errors
• Repeatibility:
– Determinism and probability
– The unexplained and the supernatural
• Corroboration: what is a “good” scientific
theory
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Demarcation: what is science?
• We need to define what is science. Common
methodology:
– INTERACTION
– QUALITY CONTROL
• In the same way, we need to agree on the meaning of
words in order to have a conversation.
• The solution has to be a CONVENTION
– dependent on history and culture
• DEMARCATION DOES NOT IMPLY RANK. ONE
DISCIPLINE IS NOT BETTER THAN ANOTHER
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Demarcation: Popper’s solution
• The currently agreed solution to
the demarcation problem is very
well described by Karl Popper:
Science is falsifiable via
experiments
• THE ESSENCE OF SCIENCE IS
THAT IT CAN BE PROVEN
WRONG
• TODAY ALL PRACTICING
SCIENTISTS ADHERE TO
THIS CONCEPT
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Karl Popper 1902-1994
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Scientific model or theory
• A scientific theory is a logically self-consistent model or
framework for describing the behavior of a related set of
natural or social phenomena.
• In general it originates from experimental evidence
• It is always corroborated by experimental evidence, in the
form of successful empirical tests.
• In this sense a theory is a systematic and formalized
expression of all previous observations that is predictive,
logical and testable (falsifiable).
• Scientific theories are always tentative, and subject to
corrections or inclusion in a yet wider theory. A model does
not aspire to be a “true” picture of reality.
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Example: gravity, from Newton
to Einstein
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Example: gravity, from Newton
to Einstein
• 1919 solar eclipse measurement: 1.61+-0.40”
• Einstein 1.75”; NewtonUCSB
0.875”
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Measurements
• Measurements must be
REPEATABLE
• Measurements have
errors
– A measurement without
an error is meaningless
– EVERY
MEASUREMENT HAS
ERRORS
– HOW TALL ARE
YOU?
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Probability and science
• The results of experiments
are often cast in terms of
probabilities.
• The same is true for
scientific theories:
Probabilistic predictions are
not in conflict with the
empirical method because
they can be falsified
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Heisenberg’s uncertainty principle
•
•
•
•
•
What does it mean?
NOT that science is not
precise
It means that some
quantities cannot be
determined
simultaneously with
infinite precision.
For example the
uncertainty on position
and momentum
(~speed) is larger than
ΔxΔp=h/2π
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A “good” scientific theory
• What constitutes a “good” scientific theory?
• If a theory can never be proven right, how is one theory better
than another?
• According to Popper:
– The better theory is the one that passes more stringent tests, both in
number and in quality
– The better theory is the more falsifiable one, if it doesn’t fail
• Old theories often become limiting cases of new theories
– (e.g. Newton vs Einstein)
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How about validating
the method?
•
•
•
•
What constitutes a “good” method?
Is the scientific method good?
Does the question even make sense?
My view is that a method is good as long as it allows you to
achieve what you want. What do you want?
• The scientific method answers some questions/obtain some
results. What are they?
• If we need to answer other questions we need different tools.
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Goal 2 – The big picture
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1.28 X 104 km
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Our solar system
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Stars in our galaxy
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More stars..
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Our galaxy. What is it?
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Our Milky Way
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Where are we in our Galaxy?
• Somewhat in the
outskirts…
• 25,000 ly away from
the center
• Moving at about 200
km/s around the
center of the Milky
Way
• TRUMPLER’s
(1930) discovery of
dust
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External Galaxies
1 - Martin
What are they? How farUCSB
are Astro
they?
How big are they?
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What are galaxies?
• Until 1923 there was a
debate on the distance
of “nebulae” (galaxies)
• Are they small objects
inside our galaxy or are
they “external”?
• Hubble settled this by
measuring the distance
to Andromeda
– A whopping 2.5 million
light years!
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The Universe is full of galaxies!
Astro
- Martin1/150,000 of the sky
10,000 galaxies in a tiny UCSB
piece
of1 sky!
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How many galaxies?
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Based on the deep fields weUCSB
estimate
of order a billion visible galaxies
Large scale structures
Billions of light years
SDSS and 2dF mapped the UCSB
positions
of about 1,000,000 galaxies 36
Astro 1 - Martin
Goal 3 - Scientific language
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Powers of 10: large numbers
Exponent tells how many times to multiply a number by
itself: 102 = 10×10 = 100
100 = 1
101 = 10
102 = 100
103 = 1000
106 = 1,000,000 (one million)
109 = 1,000,000,000 (one billion)
1012 = 1,000,000,000,000 (one trillion)
A positive exponent on the number 10 tells you how many
zeros are in the number.
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Powers of 10: small numbers
Negative exponents tell how many times to divide by ten: 10-2 = 1/10 ×
1/10 = 1/102 = 0.01
100 = 1
10-1 = 1/10 =0.1
10-2 = 1/10×1/10 = 0.01 (one hundredth)
10-3 = 1/10×1/10×1/10 = 1/103 = 0.001 (one thousandth)
10-4 = 0.0001 (one ten-thousandth)
10-6 = 0.000001 (one millionth)
You can also think of the negative exponent as how many decimal
places are in the number.
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Scientific notation
A way of expressing large or small numbers
2,230,000 = 2.23 ×1,000,000 = 2.23×106
0.0095 = 9.5 × 0.001 = 9.5×10-3
To use scientific notation on your calculator, use the EE or EXP key.
For example, 2.23 EE 6.
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Length (in Meters)
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Dimensional quantities
have units
• How much does your Universe textbook
weigh?
• How tall are you?
• Although units are arbitrary, dimensions are
not!
• If you quote a length it should be in units of
length, so time etc etc. You cannot be 5 hours
tall!
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Standard Units in Astronomy
• The standard system of units is the so-called
international system (SI), based on meters, kg,
seconds
• The system is convenient because conversion
are trivial in exponential notation:
– 1 km = 1000 m vs 1 mile = ?? feet?
• Astronomy often uses non SI units for
historical reasons.
• For example 1 solar mass ~ 2e30 Kg
• When in doubt convert to SI
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Example: length
Astronomers use the metric system (meters for distance or length).
But sometimes it is convenient to use other units. The average
distance from the Earth to the Sun is called an astronomical unit. 1
AU = 1.496×108 km
The distance light travels in a year is a lightyear (ly). The nearest
star, Proxima Centauri is 4.2 lyr away, so the light we see today left
it 4.2 years ago. Note that a lightyear is a unit of distance, not time.
The farthest thing you can see with your naked eye is M33, the
Pinwheel Galaxy, 3 million lightyears away.
What is the distance to the Sun in light minutes?
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Angles
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Degrees are divided into 60 (arc)minutes
(Arc)minutes are divided into 60 (arc)seconds
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Turning an angular distance (α) into
a linear distance (D)
First need to know how far
away the object is (d).
D = 206265
ad
The angle α must be in arcseconds. The distances can
be in any unit, as long as they are the same.
Example: What is the linear diameter of the moon if it
is half a degree wide, and 400,000 km away?
æ 60' öæ 60"ö
First, how many arcsec
0.5deg = 0.5 ç ÷ç ÷ = 1800"
è 1 øè 1' ø
are in 0.5 deg?
D=
1800"´400,000km
206265
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= 3491km
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Definition of a Parsec
• We will use units of
parsecs frequently in our
discussion of galaxies.
• 1 parsec is 3.26 light-years
• 1 parsec is 3.0856e13 cm,
or 3.056e11 m.
• The Sun is about 8
kiloparsecs from the
center of the Milky Way.
• How long would it take a
television broadcast
from the center of the
Galaxy to reach earth?
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Summary
• Goal 1 – Scientific method
– Demarcation: what is science?
– Falsification: how do you test scientific theories?
– Corroboration: what is a “good” scientific theory?
• Goal 2 – The big picture
– The Universe is huge and awesome and we will
make a “Grand Tour”
• Goal 3 – Learning scientific language
– Science terms have very precise definitions, with
sometimes somewhat different meaning than in the
current language
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Homework – Due 10/06/14
• On your own: answer all the review questions
in chapter 1
• To TAs: answer questions 1.35, 1.39
– Provides practice with small angle formula
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