AST121 Introduction to
Astronomy
High Point University
Spring, 2004
Dr. Aaron Titus
Getting to know you…
• Introduce yourself
• The one-hand ice-breaker:
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What is something you’re good at?
Where are you headed?
What is something that makes you angry?
Who do you love or what is something that you
love?
– What is something to remember you by?
Syllabus
• Course Description
– An introduction to astronomy covering the motions,
distances, and physical nature of heavenly bodies.
Topics include the history of astronomy, the scientific
method, and current views of cosmology.
• Textbook
– The Cosmos: Astronomy in the New Millenium by
Pasachoff and Filippenko
– This is required for the course and will be used
extensively.
– You should read the assigned chapter BEFORE class.
Syllabus
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Office: 342 HHSC
Email: titus@mailaps.org
Phone: 336-841-4668
Web: www.highpoint.edu/~atitus/
Class: M T Th 6:00 pm - 9:30 pm
Office hours
– Before or after class is generally a good time to find
me, but there are occasions when I’ll be unavailable.
– Email is always a good way to reach me.
Syllabus
• Grading Scale
A+ (96), A (92), A- (88), B+ (84), B (80), B- (76), C+
(72), C (68), C- (64), D+ (60), D (56), D- (52), F (<52).
• Grade Determination
– experiments and in-class activities (25%), homework
(20%), quizzes (15%), mid-term exam (20%), final
exam (20%).
• Homework
– WebAssign (https://www.webassign.net/v4.html)
WebAssign
• Your username is your High Point username
and your initial password is the same as
your username.
• Please log in tonight or tomorrow and email
immediately if you have difficulty.
• After logging in, go to “options” to change
your email address (to the one you check
most often) and your password.
My Educational Philosophy
You learn best when you are actively engaged
with the subject through activities such as
reading (and answering questions about
what you read), discussing, experimenting,
and solving problems. Lectures are useful
for motivation, but for most students
listening to lectures and copying lecture
notes is an ineffective method to learn.
My motivational speech
• Focus on learning, not on grades. Learning brings success,
and life-long learning brings life-long success.
• If I offered to hire you for one month (30 days straight!)
and offered to pay you $1,000,000 or 1 penny on the first
day, but double your wages each day, which would you
accept?
• If you take the penny, you make over 5 million dollars on
the 30th day (over 10 million for the month)
• It’s how you grow that’s important, not how much you
start with!
Chapter 1 - A Grand Tour of the
Heavens
Measurements
Scientific Notation
How big is…?
Scientific Method
Warm Up
Why should you learn about
astronomy?
Psalm 19
1 The heavens declare the glory of God;
the skies proclaim the work of his hands.
2 Day after day they pour forth speech;
night after night they display knowledge.
3 There is no speech or language
where their voice is not heard.
4 Their voice goes out into all the earth,
their words to the ends of the world.
In the heavens he has pitched a tent for the sun,
5 which is like a bridegroom coming forth from his pavilion,
like a champion rejoicing to run his course.
6 It rises at one end of the heavens
and makes its circuit to the other;
nothing is hidden from its heat.
Measuring things
• For us to communicate “how much” something is,
we must use units.
• What if I were to offer a job to you that pays an
annual salary of 60,000 per year? Would you
accept the job?
• Three fundamental units used in the SI system (SI
is the most common system of units used in
science)
– unit of mass, kilogram (kg)
– unit of distance, meter (m)
– unit of time, second (s)
Prefixes
prefix
meaning
power of 10
micro
one-millionth
10-6
1/1,000,000
milli
one-thousandth
10-3
1/1000
centi
one-hundredth
10-2
1/100
kilo
one thousand
103
1000
mega
one million
106
1,000,000
giga
one billion
109
1,000,000,000
tera
one trillion
1012
1,000,000,000,000
Scientific Notation
• There is an easier way to express numbers so that we
don’t have to count all those digits and commas.
9850 kg = 9.85 x 103 kg = 9.85 x 106 g
299,792, 458 m/s = 2.99792458 x 108 m/s
384,403 km = 3.84403 x 106 km = 3.84403 x 109 m
• The mass of the earth is 5.97 x 1024 kg. Do you
really want to write that number without using
scientific notation?
Mass
• a measure of inertia (how much net force is
needed to accelerate an object)
• independent of location in the universe
• a measure of how much “stuff” an object is
made of and what kind of “stuff” it’s made
of; it depends on the atomic composition of
which an object is made
Mass and Weight
• mass is NOT the same
thing as weight!
– near a large body such
as a planet or moon or
star, w = mg where g is
the local acceleration
due to gravity.
– g depends on the mass
of the large body
g
(m/s2)
weight
weight
(N) of
(lbs) of
Dr. Titus Dr. Titus
Earth
9.8
800
180
Moon
1.6
130
29
Jupiter
25
2050
460
Mars
3.7
300
67
Pluto
0.1
8
1.8
Body
Masses of a few common objects
Object
mass (kg)
1 liter of water
1
Earth
5.97 x 1024
Moon
7.36 x 1022
Sun
1.99 x 1030
me
82
universe
~1050
hydrogen atom
1.67 x 10-27
Distance
• “how far” one point is from another point.
• need to define the two points
– distance of the center of the moon from the center of
the earth
– distance of the center of the moon from the center of
the sun
• need a standard
– a meter, as defined by the length of a meterstick, is too
arbitrary
– a meter should be based on another unchanging and
unarbitrary value.
What about light?
• Albert Einstein made a presupposition that the
speed of light is the same in all reference frames
(i.e. no matter how fast you are traveling and no
matter what direction you’re traveling in, you will
measure the same value for the speed of light).
• Einstein also proposed that nothing travels faster
than the speed of light in a vacuum.
• The speed of light is a universal speed limit!
• The speed of light is a universal constant!
c
• c = 299,792,458 m/s and is DEFINED to be
this value.
• Therefore, in one second, light travels
299,792,458 meters.
• 1 m = the distance light travels in
1/299,792,458 second
light year
• 1 light year is the distance light travels in
one year.
• 1 ly = 9.46 x 1015 m
• It takes about 8.3 minutes for light from the
Sun to reach Earth.
distance to the Sun / speed of light = 500 seconds = 8.3 minutes
second
• Throughout history, time has been measured in various
ways.
• Astronomy has long been important in defining time.
• A month was originally measured by lunar phases, the day
is measured by the earth’s rotation about its axis, and the
year is measured by the earth’s motion about the sun.
• A day is broken into hours, hours into minutes, and
minutes into seconds.
• But what are some problems with using this method to
define a second?
second
• The time duration for Earth to rotate once about its axis (a
day) is not necessarily constant. Earth’s rate of rotation is
slowing down.
• A day cannot be measured as precisely as we would like.
• We now define a second in terms of the frequency of the
light emitted by excited electrons in cesium atoms. The
electrons emit light at a frequency of 9,192,631,770 Hz.
Thus, one second is the time required for this light to make
9,192,631,770 oscillations. The official clock of the United
States is the cesium fountain clock, NIST-F1, at NIST.
• The uncertainty of NIST-F1 is so low that it will neither
gain nor lose a second in 20 million years!
The nature of science
• Science is the systematic enterprise of gathering
knowledge about the world and organizing and
condensing that knowledge into testable theories.
• You will notice four important things in this
definition
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observing (i.e. experimenting)
developing a model for understanding and predicting
testing the model
doing this in a systematic way
“Doing” science
• There’s a definite methodology to “knowing” - we
call this the scientific method.
• The scientific method is the process of
formulating a model to explain and predict
observed phenomena.
• It’s not a single method, but rather a process that
has certain characteristics.
• There’s no correct definition of the scientific
method.
Experiment
• “The test of all knowledge is experiment.
Experiment is the sole judge of scientific ‘truth.’”
-- Richard Feynman, The Feynman Lectures on
Physics.
• Scientific theories and models are tested by
experiment. If they don’t hold up, there are two
possibilities: (1) our theory or model is incomplete
or invalid; (2) our experiment is flawed and we’ve
made invalid conclusions from our experiment.
Characteristics of the Scientific
Method
• observation or research question
• hypothesis
– Sometimes this is a creative idea based on what you
already know
– Sometimes this seems completely “off the wall”
– This is often based on a “model” which is a wellorganized concept used to explain and understand.
• experiment
– Are the results explainable by the hypothesis?
– Was the experiment well-designed?
• prediction and further testing
a few more comments...
• A model is an organized way of thinking
about something.
• A model is often approximate and has
known limitations (i.e. it’s simplistic).
• A model is our way of understanding a
complex phenomenon in a simple way.
• A model is used to formulate specific
hypotheses.
examples of models
• We might model the earth as a sphere. It’s
actually squashed at the poles.
• We might model the earth and moon as a
two-body system even though they also
orbit the sun, and the entire solar system is
also in orbit within the Milky Way, etc.
• We model solid matter as if it was made up
of atoms connected by tiny springs.
For practice
• A jar is full of candies. In a group of two,
determine how you can estimate the number
of candies in the jar without actually
counting ALL of the candies (counting a
few is acceptable)?
• Determine at least two methods.
• Estimate the number of candies in the jar.
The Universe in 11 Steps
Nightwatch
Terence Dickinson
Step 1
(20,000 km)
Step 2
(2 x
6
10
km)
Step 3 (1.2 AU, ~200 x
6
10
km)
Step 4
(120 AU)
Step 5
(12,000 AU = 0.19 light-years)
Step 6
(20 light-years)
Step 7
(2,000 light-years)
Step 8
(200,000 light-years)
Step 9 (20 million light-years)
Step 10
(2 billion light years)
Step 11
(greater than known universe)