ESCI116 LAB

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ESCI116 LAB

• Welcome to
• Stellar Astronomy Lab
• This Section T 700 1010
• Other Sections MW R(d)

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What are we doing here?

• Learning to appreciate the night sky.
• Learning to understand the scientific process
  (and its limitations).
• Learning how scientific research is done (an
  overview), specifically in astronomy.
• Learning about our LARGE SCALE environment
  (Solar System - stars - galaxies - the universe).
• Learning history the development of our modern
  world.

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Scientists do not study nature because it is
useful they study it because they delight in it,
because it is beautiful. -H. Poincare
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Goals for this course

• Understand the relationship between observation
  and knowledge.
• Value astronomy, and science in general, as human
  endeavors.
• Appreciate the dynamic nature of scientific
  knowledge.

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Syllabus

• Stuff about me
• Office effectively here (in this lab)
• You can visit with me
• 1 hr before class or 1/2 hr after -or- by
  appointment
• Can call anytime (office 626 395 1938)
• Email bauer_at_scn.jpl.nasa.gov
• I will try, as a courtesy, to post important
  material on my Web Page http//www.bauerphysics.c
  om/gerbs/gerbs.html (gerbs link)
• I want to help you learn astronomy and succeed in
  this course.

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Required stuff

• Textbook The Cosmic Perspective (Bennett et al.)
• Lab Packets, 1 2 (previous work as well)
• Other (occasionally provided)
• Calculator
• protractor
• Ruler
• notebook
• computer account (know login pswd!!!!!!!!!)

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Your Grade and What is Graded

• Each lab is worth 100 points
• There are 4 night-sky observing labs the
  schedule may change owing to logistics or weather
• Your lab grade is folded into your grade for the
  course (20-25)
• Attendance for all labs is mandatory (and
  recorded)
• Note the policy on late labs!
• 5-15 of most labs will be graded on their
  summary... I would like these in the form of an
  ABSTRACT.

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Abstract?

• Not a painting
• Usually 1 Paragraph
• Tell what you did and why you did it
• State your hypothesis somewhere (in a regular
  fashion) in the text
• Tell how you tested it
• Say what the result was, and how trustworthy the
  result is.

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Other Issues
lab

• Attendance and Absences
• Academic honesty
• Getting Help
• Talking
• Turn in Labs at START of class

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LAB 1 How Far to the Stars? Math Review

• Scientific Method
• Hypotheses
• What they are
• How they are made
• How they are tested
• Scientific Notation
• One way to determine distances to a star
• Interpreting scientific results

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The Scientific Method

• And Scientific Notation...

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What Have You Already Heard About The Scientific
Method?

• The scientific method is a way to find out about
  the universe.

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Overview of the Scientific Method
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Hypothesis

• Main Entry hypothesis
• Pronunciation hI-'pä-th-ss Function noun
  Inflected Form(s) plural hypotheses /-"sEz/
  Etymology Greek, from hypotithenai to put under,
  suppose, from hypo- tithenai to put -- more at
  DO
• 1 a an assumption or concession made for the
  sake of argument b an interpretation of a
  practical situation or condition taken as the
  ground for action
• 2 a tentative assumption made in order to draw
  out and test its logical or empirical
  consequences
• synonyms HYPOTHESIS, THEORY, LAW mean a formula
  derived by inference from scientific data that
  explains a principle operating in nature.
  HYPOTHESIS implies insufficient evidence to
  provide more than a tentative explanation lta
  hypothesis explaining the extinction of the
  dinosaursgt. THEORY implies a greater range of
  evidence and greater likelihood of truth ltthe
  theory of evolutiongt. LAW implies a statement of
  order and relation in nature that has been found
  to be invariable under the same conditions ltthe
  law of gravitationgt.

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Hypothesis

• Based on Previous Observations
• Testable
• Example (Based on common knowledge, which is(are)
  an authentic hypothesis(es)?)
• Stars are like the Sun and the same distance as
  the Sun
• The stars (and most of everything else) were made
  by an extremely (inconceivably) advanced,
  friendly alien race.
• Stars are like the Sun, but very far away

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Hypothesis

• Based on Previous Observations
• Testable
• Example (Based on common knowledge, which is(are)
  an authentic hypothesis(es)?)
• Stars are like the Sun and the same distance as
  the Sun
• The stars (and most of everything else) were made
  by an extremely (inconceivably) advanced,
  friendly alien race.
• Stars are like the Sun, but very far away

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Testing Details, Details

• it is important for your experiment to be a fair
  test meaning you must control all variables
  except one (e.g. CDC study Effects of caffeine
  in the workplace - We sampled 100 office workers
  at random on Jan 1st, 2000. We assumed the
  subjects to be well-rested and relatively free of
  toxins...)
• openness -gt others must be able to see and test
  your results
• reproducibility -gt others must be able to redo
  your experiment and get the same results
• simplicity -gt the simplest explanation is usually
  the best

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Types of Measurements

• humans can perform 2 kinds of measurements
  quantitative qualitative
• quantitative (numerical) measurements are more
  important to modern astronomy
• each quantitative measurement consists of a
  quantity and a unit

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Quantities Units
Quantity a specified amount or number of
something
Unit an agreed-upon quantity that is used to
express other quantities
examples distance mass speed time area . . .
examples meter kilogram meters per second
second square meter . . .
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What are the Quantities Units?
You must include units or quantitative
measurements wont make sense
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If You Leave Off the Units . . .

• other people cant tell what youre doing
• this can have serious consequences!

Mars Polar Lander
Cost over 20 million
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Metric Units

• astronomers generally use metric units (e.g.
  meter, kilogram, Watt, etc.)
• but they also also use a few non-metric units
  (year, light-year, second)
• imperial units ( pounds, miles, gallons,) are
  fine for everyday use, but less helpful in
  science.

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Scales in the Universe

• 1 atom is about 0.000000000106meters (an
  Angstrom, Å)

Å

• 1 adult person is about 1.5-2 meters

1.3 meters?
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Scales in the Universe

• Earth is about 12,756,000 meters
• The Solar System out to Neptune is about
  4,500,000,000,000 meters (30 AU)

• Midway to the next star is 6,200,000,000,000,000
  meters (40000AU, 2 ly)

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Scales of the Universe

• The distance to the CENTER of OUR galaxy is
  90,000,000,000,000,000,000 m (30,000 ly)
• The nearest galaxy (besides ours) is
  7,500,000,000,000,000,000,000 m (2,500,000 ly)

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Scales of the Universe

• The Coma cluster of galaxies (a fairly close one)
  is 770,000,000,000,000,000,000,000 m
  (250,000,000 ly)

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Scientific Notation

• Why do we need it?
• Scales of distance, mass, time or just about
  anything can be extremely large or small.
• It gets tedious carrying around all those 0s
• It also allows us to make a statement about a
  numbers accuracy

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Scientific Notation

• A number in Scientific notation has 3 parts
• Coefficient (between /-1.0 and /-9.9999999999)
• Exponent (represents the powers of ten in
  standard notation)
• Positive lots of zeros behind the Coefficient in
  standard notation
• Negative lots of zeros behind the decimal point
  and in front of the Coefficient in standard
  notation
• Units

Size of atom 1.06 ? 10-10 m Distance to the
Coma Cluster 7.7 ? 1023 m
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There and back again

• From Standard to Scientific
• Move the decimal point to come after the first
  nonzero digit.
• Number of places the decimal point moves
  indicates the power of ten in the exponent. The
  exponent is positive if the decimal point moves
  to the left, negative if it moves to the right.
• From Scientific to standard
• The exponent (power of 10) indicates how many
  places to move the decimal point move it to the
  right if the exponent is positive, and to the
  left if its negative.
• If moving the decimal point creates open spaces,
  fill them in with zeros.

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Extra Steps

• Round the number (down if lt half, up otherwise)
  to the least significant digit e.g. when dealing
  with scientific notation, quote the coefficient
  to the length of the values with the shortest
  coefficients.
• ALWAYS include your units.
• EXAMPLE (a silly one) (Size of Atom) ? (distance
  to the Coma Cluster) (1.06 ? 10-10 m) ? (7.7 ?
  1023 m) 8.2 ? 1013 m2 (or square meters)

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Useful Stuff

• You should be able to do
• simple algebra geometry,
• handle exponents roots,
• and log relations
• complete the MATH REVIEW.
• NB At this level, math is a TOOL (not a code
  or language, but a handy set of procedural
  rules to make your life easier).

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Scientific Notation Calculators

• only scientific calculators let you work with
  scientific notation
• basic calculators or cell phones are not good
  enough
• try to obtain your own scientific calculator

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Basic Operations With Scientific Calculators

• entering a number ( try 5.97 x 1024 kg and 2.5 x
  10-11 m)
• multiplying or dividing two numbers ( try 3.34 x
  109 m / 6.12 x 107 s )
• adding or subtracting two numbers ( try 2.27 x
  1019 m 4.80 x 1022 m)

Note you can only add subtract quantities that
are expressed in the same units!
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Todays Assignment

• Do the math exercises in groups of 2 - 4
• Feel free to help check answers with each other
  -- but make sure to learn how to do these
  calculations on your own.
• If your whole group is confused, please ask your
  instructor for help.

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TAKE A BREAK

• 10 min (SHARP!) then lets do the math-part of
  the lab.
• The math part of the lab is due at the START of
  class next week.
• IN 2 WEEKS We meet HERE to go to the Observing
  Spot (Equestrian Park Map) for our First
  OBSERVING lab.

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More Useful Stuff to review angles

• 360 deg full circle 2 pi radians 24 hrs
  (time-wise)
• 1 arcmin 1/60th of a deg, 1arcsec 1/60 of
  arcmin.
• converting degrees to motion of the starts in the
  sky 15 deg 1 hour, 15 arcmin 1 min, 15
  arcsec 15 sec

• The angle subtended by your thumb at arms
  length- 2-ish deg.
• Angle of the Moon- 0.5 deg.
• fist at arms length - 10 deg
• open hands at arms length - 20 deg

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Stellar Magnitudes
(The Sun in X-ray FE XII 195A)
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Which star is giving off more light?

• Brightness How bright a star appears.
• Luminosity How much light the star is actually
  giving off.

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How do we measure these?

• Brightness How bright a star appears.
• Luminosity How much light the star is actually
  giving off.

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Apparent Magnitude Scale

• Introduced by Hipparchus (160-127 B.C.)
• Think about the order in which stars appear. The
  lower the number, the brighter the star.
• In what order would the stars Fomalhaut (2),
  Pollux (1), Arcturus (0), and Achernar (-1)
  become visible in the evening sky?

Venus (-4) Sun (-26)
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What does it measure?

• measures ratios of actual amount of light energy
  received
• receive 2.5x more energy from a mag 1 star than a
  mag 2 star
• difference of 5 magnitudes is 100x difference in
  received energy

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Its the difference that matters
7.8
2.5X2.5 6.25 X
6.8
5.8
4.8
3.8
2.8
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Problem

• Rigel Kent. aka ?-Centauri (0.0 mag)
• Spica (1.0 mag)
• Which looks brighter?
• How much more light do we receive from it?
• One level of magnitude means 2.5 times more light
  received !!

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BUT...

• Spica is actually more than 1000x more luminous
  than Rigel!!
• If Spica is putting out more light, why might it
  appear dimmer in the sky?

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One over r squared
2 feet
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One over r squared
B/2 ???
B
A
4A
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One over r squared
B/4
B
A
4A
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Question
Stars A and B are known to have the same
luminosity. The distances to the two stars are
given.
A
B
4 ly
12 ly
What can you conclude about their brightnesses?
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Absolute Magnitude

• Tells us LUMINOSITY of a star
• Apparent would work if everything were at the
  same distance
• Basically, it is the apparent magnitude of the
  star if it were placed 32 ly (10 pc) away

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Abstract

• Tell what you did and why you did it
• State your hypothesis somewhere (in a regular
  fashion) in the text
• Tell how you tested it
• Say what the result was, and how trustworthy the
  result is.

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Different Question
Both stars have apparent magnitude 4
A
B
4 ly
8 ly
What can you conclude about their luminosities?
How do we find distance?
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Problems with Large Lecture Courses

• Really difficult to get to know everyone
• Students cant hear or see what is being
  presented
• Everyones a little scared to comment or ask
  questions
• Student-student and teacher-student interaction
  is difficult