ASTR 111

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Lecture 2

• ASTR 111 Section 002
• Introductory Astronomy
• Solar System

Dr. Weigel
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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

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Outline

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

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B
A

1. What is the angular distance between points A and
   B on this slide (In degrees and arcminutes).
   Each student should take their own measurement.
   Each student should also write down their height
   alongside of their measurement.
2. Predict what will happen if you made your
   measurement in two different parts of the room.
3. Next week you sit in the same chair but weigh 30
   pounds less. Will your (angular) measurements
   change?
4. Do you think there will be a relationship between
   a persons height and the angle they measure?

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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

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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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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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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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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
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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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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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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Outline

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