ASTR 111

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Lecture 2

• ASTR 111 Section 002
• Introductory Astronomy
• Solar System

Dr. Weigel
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http//www.astro.ljmu.ac.uk/courses/phys134/magcol
.html
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Reading for this week

• The reading for this week is Chapter 1 (all) and
  Chapter 2 (sections 2.1-2.2 only)
• The quiz will cover this reading and the topics
  covered in this weeks lectures
• The quiz will be available on BlackBoard at 1015
  am noon today.

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A note on lecture notes
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Outline

• Angular Measurements Review
• Accuracy, Precision, and Bias
• The Scientific Method
• Astronomical Distances
• Ancient Astronomy

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Angular Measurements Result
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B
A

1. What is the angular distance between points A and
   B on this slide (In degrees and arcminutes).
   Answer depends on where you are sitting. To get
   arcminutes, take angle in degrees and multiply by
   60.
2. Predict what will happen if you made your
   measurement in two different parts of the room.
   Relative to the middle of the room (1) as you
   move to the front of the room, angular distance
   should increase (2) as you move to the walls,
   angular distance should decrease.

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B
A

1. Do you think there will be a relationship between
   a persons height and the angle they measure? A
   shorter person will have smaller fingers -gt
   larger angular measurements. A shorter person
   will have shorter arms -gt smaller angular
   measurements. (Try to simulate this with your
   hand and arm!) Based on this, the answer is that
   we dont expect them to have different angular
   measurements.

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B
A

• Next week you sit in the same chair but weigh 30
  pounds less. Will your (angular) measurements
  change?
• If you used the width of your hand or the width
  of your finger to measure, you would expect the
  angular distance you measured to increase
  (skinnier hand and finger).
• If you used the distance between your knuckles on
  your finger, you would not expect a change in
  your measurement (if you lose weight, the
  distance between your knuckles is not expected to
  change because your bone size should not change).

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http//antwrp.gsfc.nasa.gov/apod/ap071025.html
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Outline

1. Angular Measurements
2. Accuracy, Precision, and Bias
3. The Scientific Method
4. Astronomical Distances
5. Ancient Astronomy

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Precision, Accuracy, and Bias

• Whenever you take measurements, you should
  account for them
• Fundamental terms that you must understand when
  interpreting measurements
• Not covered in your book

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Accuracy vs. Precision
Target is red
Shots are black
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Accuracy vs. Precision
Target is red
Shots are black
High precision Low accuracy
High precision High accuracy
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Accuracy vs Precision
Mnemonic Youll get an A for Accuracy
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Bias
Target is red
Shots are black

• The left target shows bias the measurements
  were made with high precision, but the were
  consistently off in the same direction.

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Summary

• Accuracy all measurements or values are
  clustered around the true value (youll get an A
  for accuracy, because you are on the true value)
• Precision all measurements are clustered but
  are not centered on true value
• Bias measurements are not centered on true value

Center of red dot is true value
No bias
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Group work ( 4 minutes)

• Draw a diagram like the ones on the previous
  slide that show
• Low precision and high bias
• High accuracy and very low precision
• On a piece of paper, write down
• Possible causes of low accuracy be specific!
  (Dont say human error)
• Possible causes of bias be specific!
• associated with your angular measurements

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Question 1.
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Question 1.
Impossible to have both High accuracy and very
low precision.
But you can have moderate accuracy and moderate
precision
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Question 2.

• Low accuracy because of moving hand and
  difficulty in lining up dots exactly
• Low precision because you are using scale that
  increments in degrees
• Bias could happen if your hand (or everyones
  hand in group) was exceptionally large. Then
  everyone would measure angle to be smaller than
  it really is.

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Group work ( 3 minutes)

• Which diagram best represents the statement
  Preliminary polling results indicated that Obama
  won Virginia by a landslide because the
  preliminary poll results were all from Northern
  Virginia.

B
D
A
C
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Group work ( 3 minutes)

• Which diagram best represents the statement
  Preliminary polling results indicated that Obama
  won Virginia by a landslide because the
  preliminary poll results were all from Northern
  Virginia.

B
D
A
C
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Outline

1. Angular Measurements
2. Accuracy, Precision, and Bias
3. The Scientific Method
4. Astronomical Distances
5. Ancient Astronomy

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The Scientific Method
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What is Science?

1. A set of facts
2. Something that professional scientists do
3. The underlying Truth about the Universe
4. The collection of data and formation of a
   hypothesis
5. None of the above

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What is Science?1) A set of facts?

• We are constantly making new discoveries and
  collecting new data
• Technology and experiments are changing
• Old Theories are replaced by new Theories
• Scientific Facts''

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What is Science?2) A thing that professional
scientists do?

• What is a scientist?
• Do you need a PhD?
• Amateur Scientists play an important role in
  discovery
• Being scientific DOES NOT required a Union Card

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What is Science?3) The underlying Truth about
the Universe?
Capitalization, too much? Suspect a Scientist
should be.
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What is Science?4) The collection of data and
formation of a hypothesis

• No, but getting closer

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What is Science?5) The collection of data and
formation of a hypothesis

• None of the above

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What is Science?

• A system of knowledge covering general truths or
  the operation of general laws especially as
  obtained and tested through the scientific method

http//www.merriam-webster.com/dictionary/science
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The Scientific Methodthe process

• characterization of existing data
• formulation of a hypothesis
• formulation of a predictive test
• experimental testing, (important error
  elimination and characterization)
• report and peer review
• validate or revise hypothesis

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Cat Scientist
http//shakespearessister.blogspot.com/2009/08/cat
-experiments.html
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Comment on reddit.com

• Ask a Question -Is what i'm seeing my reflection
  or another cat?
• Do Background Research - Go to other mirror to
  determine what true reflection looks like
• Construct a Hypothesis - The other cat is my
  reflection.
• Test Your Hypothesis by Doing an Experiment -
  move myself. see if reflection duplicates my
  motions as in the mirror.
• Analyze Your Data and Draw a Conclusion - I am
  seeing another cat
• Communicate Your Results - have my master post on
  reddit

http//www.reddit.com/r/science/comments/9e1vh/oli
via_the_cat_doublechecks_if_similar_cat_beyond/
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Important

• Science is a process
• Humans have concluded that this is the best
  process by which to explain observations

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Outline

1. Angular Measurements
2. Accuracy, Precision, and Bias
3. The Scientific Method
4. Astronomical Distances
5. Ancient Astronomy

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Parallax
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Parallax
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Parallax
10 20 30 40 50 60 70 80 90
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Parallax

• When the apparent position of an object (numbers
  on speedometer) changes because of the change in
  position of the observer (drivers seat to
  passengers seat).

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Another example
http//www.astro.ljmu.ac.uk/courses/phys134/magcol
.html
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The Parsec
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Astronomical distances are never measured in Car
hours, dotsecs, and Moon Units

• Car Hour (ch)
• the distance a car can travel in one hour at a
  speed of about 60 miles/hour. How far is
  Baltimore? About an hour.
• Car Year (cy)
• the distance a car can travel in one year at a
  speed of about 60 miles/hour
• dotsec (ds)
• the distance at which the two dots on the screen
  subtend an angle of 1 arcsec
• Moon Unit (MU)
• One Moon Unit is the average distance between
  Earth and the Moon

A time
A distance
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Astronomical distances are often measured in
astronomical units, parsecs, or light-years

• Light Year (ly)
• One ly is the distance light can travel in one
  year at a speed of about 3 x 105 km/s or 186,000
  miles/s
• Parsec (pc)
• the distance at which 1 AU subtends an angle of 1
  arcsec or the distance from which Earth would
  appear to be one arcsecond from the Sun
• Astronomical Unit (AU)
• One AU is the average distance between Earth and
  the Sun
• 1.496 X 108 km or 92.96 million miles

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Sun
Earth
Observers view of Sun and Earth from outer planet
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Gods-eye view - Looking down on Sun and Earth
Observers view

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Gods-eye view
Observers view
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(No Transcript)
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Group Problem

• Form groups of exactly 4
• Optimal configuration is two students in one row
  and two students in another row

No
Yes
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1. Imagine that you are looking at the stars from
   Earth in January. Use a straightedge to draw a
   line from Earth in January, through the nearby
   star (Star A), out to the Distant Stars. Which
   of the distant stars would appear closest to Star
   A in your night sky in January. Circle this
   distant star and label it Jan.
2. Repeat Question 1 for July and label the distant
   star July.
3. In the box below, the same distant stars are
   shown as you would see them in the night sky.
   Draw a small x to indicate the position of Star A
   as seen in January and label it Star A Jan.
4. In the same box, draw another x to indicate the
   position of Star A as seen in July and label it
   Star A July.
5. Describe how Star A would appear to move among
   the distant stars as Earth orbits the Sun
   counterclockwise from January of one year,
   through July, to January of the following year.
6. Consider two stars (C and D) that both exhibit
   parallax. If Star C appears to move back and
   forth by a greater amount than Star D, which star
   do you think is actually closer to you? If
   youre not sure, just make a guess. Well return
   to this question later in this activity.

Distant Stars
Nearby Star (Star A)
1 AU
Earth (July)
Earth (January)
Based on Lecture Tutorials for Introductory
Astronomy, Prather et al., pg 35
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Star A Jan
Star A July

1. and 2.

Distant Stars
Nearby Star (Star A)
1 AU
Earth (July)
Earth (January)
Based on Lecture Tutorials for Introductory
Astronomy, Prather et al., pg 35
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3. And 4.
Jan
July
Nearby Star (Star A)
Star A January
Star A July
1 AU
Earth (July)
Earth (January)
Based on Lecture Tutorials for Introductory
Astronomy, Prather et al., pg 35
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Jan
July
Nearby Star (Star A)
Star A January
Star A July
5. From January till July, star A appears to move
to the left relative to the distant stars. From
July till January, star A appears to move to the
right.
1 AU
Earth (July)
Earth (January)
Based on Lecture Tutorials for Introductory
Astronomy, Prather et al., pg 35
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6.Consider two stars (C and D) that both exhibit
parallax. If Star C appears to move back and
forth by a greater amount than Star D, which star
do you think is actually closer to you? If
youre not sure, just make a guess.
Jan
July
Nearby Star (Star A)
Star C is closer
1 AU
Earth (July)
Earth (January)
Based on Lecture Tutorials for Introductory
Astronomy, Prather et al., pg 35
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6.Consider two stars (C and D) that both exhibit
parallax. If Star C appears to move back and
forth by a greater amount than Star D, which star
do you think is actually closer to you? If
youre not sure, just make a guess.
Jan
July
Star C
Star C is closer
1 AU
Earth (July)
Earth (January)
Based on Lecture Tutorials for Introductory
Astronomy, Prather et al., pg 35
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6.Consider two stars (C and D) that both exhibit
parallax. If Star C appears to move back and
forth by a greater amount than Star D, which star
do you think is actually closer to you? If
youre not sure, just make a guess.
(Star D)
Star C is closer.
1 AU
Earth (July)
Earth (January)
Based on Lecture Tutorials for Introductory
Astronomy, Prather et al., pg 35
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(No Transcript)
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Group Question

1. If you close one eye and hold out your index
   finger, your finger appears to cover an object.
   If you switch eyes, your finger no longer covers
   that object. With a diagram, explain why.
2. How does what you observe change with the
   distance of your arm from your face?

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(No Transcript)
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1. If you close one eye and hold out your index
   finger, your finger appears to cover an object.
   If you switch eyes, your finger no longer covers
   that object. With a diagram, explain why. See
   right
2. How does what you observe change with the
   distance of your arm from your face? As you move
   finger closer, distance object seems to jump.

Finger
Top of head
Left eye
Right eye
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Group question

1. How many light-years are in 10 parsecs?
2. How many light-years could a human travel in a
   space craft?
3. Which is larger, a parsec or an AU?
4. Why do you think we have two units, the parsec
   and the light year, when they are so close to
   each other? (1 parsec 3.26 light-years)

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Group question

• 1. How many light-years are in 10 parsecs?

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Group question

• 2. How many light-years could a human travel in a
  space craft?
• Somewhere between 0 and 100 light-years, if the
  were traveling at the speed of light. (Human
  lifetime)
• A light-year is the distance light travels in one
  year.

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Group question

• 3. Which is larger, a parsec or an AU?
• A parsec is much larger

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Group question

• 4. Why do you think we have two units, the parsec
  and the light year, when they are so close to
  each other? (1 parsec 3.26 light-years)
• Light-year is useful for expressing distances
  when we want to know how long light will take to
  move across that distance
• Parsec is useful when we are looking at angular
  sizes An object that subtends 1 arc-second in
  the sky will be a distance of 1 parsec.

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Distant Stars

• To describe the distances to stars, astronomers
  use a unit of length called the parsec. One
  parsec is defined as the distance to a star that
  has a parallax angle of exactly 1 arcsecond.

PA
Earth (July)
Earth (January)
Based on Lecture Tutorials for Introductory
Astronomy, Prather et al., pg 35
68

• If the parallax angle for Star A (PA) is 1
  arcsecond, what is the distance from the Sun to
  Star A? (Hint use parsec as your unit of
  distance.) Label this distance on the diagram.
• Is a parsec a unit of length or a unit of angle?
  (It cant be both.)
• As Star A moves outward, what happens to its
  parallax angle?

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Distant Stars

• To describe the distances to stars, astronomers
  use a unit of length called the parsec.
• One parsec is defined as the distance to a star
  that has a parallax angle of exactly 1 arcsecond.

1 parsec
PA
Earth (July)
Earth (January)
Based on Lecture Tutorials for Introductory
Astronomy, Prather et al., pg 35
70

• If the parallax angle for Star A (PA) is 1
  arcsecond, what is the distance from the Sun to
  Star A? (Hint us parsec as your unit of
  distance.) Label this distance on the diagram.
• Is a parsec a unit of length or a unit of angle?
  (It cant be both.)
• As Star A moves outward, what happens to its
  parallax angle?

1 parsec
Length
Decreases
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Outline

1. Angular Measurements
2. Accuracy, Precision, and Bias
3. The Scientific Method
4. Astronomical Distances
5. Ancient Astronomy

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Ancient Astronomy
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http//www.google.com/sky/
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Naked-eye astronomy had an important place in
ancient civilizations

• Positional astronomy
• the study of the positions of objects in the sky
  and how these positions change
• Naked-eye astronomy
• the sort that requires no equipment but human
  vision
• Extends far back in time
• British Isles Stonehenge
• Native American Medicine Wheel
• Aztec, Mayan and Incan temples
• Egyptian pyramids

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Stonehenge
http//archaeoastronomy.wordpress.com/2005/06/15/s
tonehenge-astronomy-ii-solar-alignments/ See also
http//news.bbc.co.uk/2/hi/uk_news/england/wiltshi
re/7465235.stm
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Aztec, Mayan and Incan temples
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Eighty-eight constellations cover the entire sky

• Ancient peoples looked at the stars and imagined
  groupings made pictures in the sky
• We still refer to many of these groupings
• Astronomers call them constellations (from the
  Latin for group of stars)

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Modern Constellations

• On modern star charts, the entire sky is divided
  into 88 regions
• Each is a constellation
• Most stars in a constellation are nowhere near
  one another
• They only appear to be close together because
  they are in nearly the same direction as seen
  from Earth