Transcript Lecture 1 - Main Page - Weigel's Research and Teaching Page

Lecture 2
ASTR 111 – Section 002
Introductory Astronomy:
Solar System
Dr. Weigel
http://www.astro.ljmu.ac.uk/courses/phys134/magcol.html
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 week’s lectures
– The quiz will be available on BlackBoard at
10:15 am … noon today.
A note on lecture notes
Outline
•
•
•
•
•
Angular Measurements Review
Accuracy, Precision, and Bias
The Scientific Method
Astronomical Distances
Ancient Astronomy
Angular Measurements Result
A
B
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.
A
B
3. Do you think there will be a relationship
between a person’s height and the angle
they measure? A shorter person will
have smaller fingers -> larger angular
measurements. A shorter person will
have shorter arms -> smaller angular
measurements. (Try to simulate this with
your hand and arm!) Based on this, the
answer is that we don’t expect them to
have different angular measurements.
B
A
4. 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).
http://antwrp.gsfc.nasa.gov/apod/ap071025.html
Outline
1.
2.
3.
4.
5.
Angular Measurements
Accuracy, Precision, and Bias
The Scientific Method
Astronomical Distances
Ancient Astronomy
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
Accuracy vs. Precision
Target is red
Shots are black
Accuracy vs. Precision
Target is red
Shots are black
High precision
Low accuracy
High precision
High accuracy
Accuracy vs Precision
Mnemonic:
You’ll get an A
for Accuracy
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.
Summary
• Accuracy – all measurements or
values are clustered around the
true value (you’ll 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
Group work (~ 4 minutes)
1. Draw a diagram like the ones on the
previous slide that show
1. Low precision and high bias
2. High accuracy and very low precision
2. On a piece of paper, write down
•
Possible causes of low accuracy – be
specific! (Don’t say “human error”)
• Possible causes of bias – be specific!
associated with your angular measurements
Question 1.
Question 1.
Impossible to have
both High accuracy and
very low precision.
But you can have
moderate accuracy
and moderate
precision
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
everyone’s hand in group) was
exceptionally large. Then everyone would
measure angle to be smaller than it really
is.
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”.
A
B
C
D
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”.
A
B
C
D
Outline
1.
2.
3.
4.
5.
Angular Measurements
Accuracy, Precision, and Bias
The Scientific Method
Astronomical Distances
Ancient Astronomy
The Scientific Method
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
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''
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
What is Science?
3) The underlying Truth about the Universe?
Capitalization, too
much? Suspect a
Scientist should be.
What is Science?
4) The collection of data and formation of a hypothesis
• No, but getting closer
What is Science?
5) The collection of data and formation of a hypothesis
• None of the above
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
The Scientific Method
the 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
Cat Scientist
http://shakespearessister.blogspot.com/2009/08/cat-experiments.html
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/olivia_the_cat_doublechecks_if_similar_cat_beyond/
Important
• Science is a process
• Humans have concluded that this is the
best process by which to explain
observations
Outline
1.
2.
3.
4.
5.
Angular Measurements
Accuracy, Precision, and Bias
The Scientific Method
Astronomical Distances
Ancient Astronomy
Parallax
Parallax
Parallax
10
20
30
40
50
60
70
80
90
Parallax
• When the apparent position of an object
(numbers on speedometer) changes
because of the change in position of the
observer (driver’s seat to passenger’s
seat).
Another example
http://www.astro.ljmu.ac.uk/courses/phys134/magcol.html
The Parsec
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.
A time
• Car Year (cy)
A distance
– 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
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
Earth
Sun
Observer’s view of Sun and
Earth from outer planet
Gods-eye view Looking down on
Sun and Earth
Observer’s view
“
Gods-eye view
Observer’s view
Group Problem
• Form groups of exactly 4
• Optimal configuration is two
students in one row and two
students in another row
No
Yes
1.
2.
3.
4.
5.
6.
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.
Repeat Question 1 for July and label the distant
star “July”.
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.”
Distant Stars
Nearby Star
(Star A)
In the same box, draw another x to indicate the
position of Star A as seen in July and label it “Star
A July”.
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.
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 you’re
not sure, just make a guess. We’ll return to this
Earth
question later in this activity.
(January)
Based on Lecture Tutorials for Introductory Astronomy, Prather et al., pg 35
1 AU
Earth
(July)
Star A July
Star A Jan
1. and 2.
Distant Stars
Nearby Star
(Star A)
1 AU
Earth
(January)
Based on Lecture Tutorials for Introductory Astronomy, Prather et al., pg 35
Earth
(July)
3. And 4.
Jan
July
Star A July
Nearby Star
(Star A)
Star A January
1 AU
Earth
(January)
Based on Lecture Tutorials for Introductory Astronomy, Prather et al., pg 35
Earth
(July)
Jan
July
Nearby Star
(Star A)
Star A July
Star A January
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.
Based on Lecture Tutorials for Introductory Astronomy, Prather et al., pg 35
1 AU
Earth
(January)
Earth
(July)
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 you’re not
sure, just make a guess.
Jan
July
Nearby Star
(Star A)
Star C is closer
1 AU
Earth
(January)
Based on Lecture Tutorials for Introductory Astronomy, Prather et al., pg 35
Earth
(July)
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 you’re not
sure, just make a guess.
Jan
July
Star C
Star C is closer
1 AU
Earth
(January)
Based on Lecture Tutorials for Introductory Astronomy, Prather et al., pg 35
Earth
(July)
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 you’re not
sure, just make a guess.
(Star D)
Star C is closer.
1 AU
Earth
(January)
Based on Lecture Tutorials for Introductory Astronomy, Prather et al., pg 35
Earth
(July)
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?
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
Left eye
“jump”.
Finger
Top of head
Right eye
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)
Group question
1. How many light-years are in 10 parsecs?
10 parsec 3.26 light - year
x
 32.6 light - years
1
1parsec
Group question
2. How many light-years could a human
travel in a space craft?
• Somewhere between 0 and 100 lightyears, if the were traveling at the speed of
light. (Human lifetime)
• A light-year is the distance light travels in
one year.
Group question
3. Which is larger, a parsec or an AU?
• A parsec is much larger
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.
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
(January)
Based on Lecture Tutorials for Introductory Astronomy, Prather et al., pg 35
Earth
(July)
• 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 can’t be both.)
• As Star A moves outward, what happens
to its parallax angle?
Distant Stars
One parsec is defined as
the distance to a star that
has a parallax angle of
exactly 1 arcsecond.
PA
Earth
(January)
Based on Lecture Tutorials for Introductory Astronomy, Prather et al., pg 35
1 parsec
To describe the distances to
stars, astronomers use a
unit of length called the
parsec.
Earth
(July)
• 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 can’t be both.)
• As Star A moves outward, what
happens to its parallax angle?
1 parsec
Length
Decreases
Outline
1.
2.
3.
4.
5.
Angular Measurements
Accuracy, Precision, and Bias
The Scientific Method
Astronomical Distances
Ancient Astronomy
Ancient Astronomy
http://www.google.com/sky/
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
Stonehenge
http://archaeoastronomy.wordpress.com/2005/06/15/stonehenge-astronomy-ii-solar-alignments/
See also http://news.bbc.co.uk/2/hi/uk_news/england/wiltshire/7465235.stm
Aztec, Mayan and Incan temples
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”)
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