Environmental Science/Physics
141: Astronomy
Steve Dutch
LS 463
465-2246
dutchs@uwgb.edu
www.uwgb.edu/dutchs
WARNING!
• “I thought this was going to be about
astronomy. There was all this chemistry and
physics!”
– CCQ Comment
Astronomy is Chemistry and Physics
• That’s why the course is cross-listed with
Physics
• Physics is how we know what the stars are,
and how they work
• Chemistry is about what everything –
including you – is made of
• I will try to keep the pain manageable
• Cognitive dissonance will not hurt you, and it
goes away
A Few Things You Really Need to
Know First
College is not High School
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Less time in the classroom
Much more independent study needed
Less homework
More complex and labor intensive
Fewer quizzes
You have to monitor your progress
May look deceptively easy
Astronomy Final Fall 2008
Score
90+
80-89
70-79
60-69
59-
Number of Students
3
10
20
19
30
What Do You Need to Build a
House?
Materials – Plans - Methods
What Do You Need to Learn in
College?
• Facts (Materials)
• Relationships (Plans)
• Processes (Methods)
Example: The Sun
• Facts:
– Size, Mass, Distance, Layers, Composition
• Relationships:
– Holds solar system together by gravity
– Supplies energy to planets
• Processes:
– Gets energy by nuclear fusion
– How planets absorb and retain heat
– How gravity and inertia result in orbits
The Two Most Amazing Ideas in
Science
• The Sun is a Star
• We Are Made of Star-Stuff
About Learning Science
• It may be different than you expect
• Two questions you may not think to ask
– How do we know?
– What good is it?
• You have a lot of assimilated information
about non-scientific subjects
• Much of what people think they know about
science is wrong
Essential Points
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Everything in Science is Metric
Scientific Notation
Temperature
About Light
Measuring size in the sky
Astronomical Distances
How Telescopes Work
Some symbols to know
• > Greater Than
• < Less than
• ~ Approximately
In Science, Everything is Metric
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1 centimeter = 0.4 inches
1 meter = 39.4 inches = 1 yard +
1 kilometer = 5/8 mile: 5 mi = 8 km
1 kilogram = 2.2 pounds
Unit of time = second
All other quantities (energy, etc.) are
combinations of kilograms, meters, and seconds
• U.S. is the only major country not using the
metric system
• Your foreign customers use metric. Deal with it
1. Everything in Science is Metric
Important Metric Prefixes
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Nano = 1/1,000,000,000
Micro = 1/1,000,000
Milli = 1/1000
Centi = 1/100
Kilo = 1000
Mega = 1,000,000
Giga = 1,000,000,000
Tera = 1,000,000,000,000
1. Everything in Science is Metric
Astronomical Numbers
• It’s no accident that large numbers are called
“Astronomical.”
• Mass of Sun:
2,000,000,000,000,000,000,000,000,000,000,000 kg
• Distance to Alpha Centauri:
43,000,000,000,000 km
• Number of Stars in Milky Way Galaxy:
400,000,000,000
• Age of Universe: 13,000,000,000 years
2. Scientific Notation
Scientific Notation
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1,2,3,4,5,6,7,8,9
10,20,30,40,50,60,70,80,90,99
100, 200,300 …… 900,999
10 x 10 x 10 = 103
The small digit (the exponent) is the number of
times we multiply 10 to get the number
• 500,000 = 5 x 100,000 = 5 x 105
• Exponent = Number of Digits – 1
• If it’s a round number, Exponent = Number of
Zeros
2. Scientific Notation
Astronomical Numbers
In Scientific Notation:
• Mass of Sun: 2 x 1030 kg
• Distance to Alpha Centauri:
4.3 x 1013 km
• Number of Stars in Milky Way Galaxy:
4 x 1011
• Age of Universe: 1.3 x 1010 years
2. Scientific Notation
Working With Scientific Notation
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100,000 x 10,000 = 1,000,000,000
105 x 104 = 109
To Multiply, Add Exponents
100,000,000/1000 = 100,000
108 / 103 = 105
To Divide, Subtract Bottom Exponent from Top
No Easy Rules for Addition and Subtraction
2. Scientific Notation
Tiny Numbers
• 100 / 10,000 = 1/100 = .01
• 102 / 104 = 10-2
• Negative Exponents mean numbers less than
1
• .01 = 1/100, so 10-2 = 1/102
• Exponent = - 1 x (Leading Zeros + 1)
• .00362 = 3.62 x 10-3
2. Scientific Notation
And Now The Most Confusing Part
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10 = 101
.1 = 10-1
10 x .1 = 1
101 x 10-1 = 100 = 1
Therefore Anything to the Zero Power = 1
“But How Can it be 1 When It’s 0??!!”
2. Scientific Notation
Zero Power Is Just A Label
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1000 = 10 x 10 x 10 = 103
100 = 10 x 10 = 102
10 = 10 = 101
1 = 10 no times = 100
.1 = 1/10 = 10-1
.01 = 1/(10 x 10) = 10-2
.001 = 1/(10 x 10 x 10) = 10-3
2. Scientific Notation
Temperature
• Scientists use the Celsius (Centigrade) scale
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32 F = 0 C (Water freezes)
212 F = 100 C (Water boils)
-40 F = -40C (Scales Equal)
One C degree = 1.8 F degrees
All atomic motion stops at -273 C (Absolute Zero)
• Kelvin Scale starts at Absolute Zero
• K = C + 273
• For Stellar temperatures, makes little difference
3. Temperature
About Light
• Light is made up of waves
– Oscillating electrical and magnetic fields
– Collectively called Electromagnetic Radiation
– Speed = 298,000 km/sec (symbol: c)
– Wavelength = distance between waves (λ)
– Frequency = number of waves per second
– One hertz = 1 wave per second
– Wavelength x Frequency = c
– Generally, radiation interacts with objects bigger
than its wavelength
4. About Light
Electromagnetic Spectrum
• Radio
– AM = 1000 kHz: λ = 300 meters
– FM = 100 MHz: λ = 3 meters
• Microwaves (a few cm)
• Infrared: λ = 1 cm – 7 x 10-7 m (700 nm)
• Visible light: 700 - 400 nm
• Ultraviolet: 400 – 1 nm
• X Rays: 1 - .01 nm (Atom = 0.1 nm)
• Gamma Rays: <.01 nm
4. About Light
Visible Light
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Red = 700 nm (4 x 1014 Hz)
Orange
Yellow
Green = 550 nm
Blue
Indigo (we need a vowel for the mnemonic)
Violet = 400 nm (7 x 1014 Hz)
Roy G. Biv
4. About Light
Visible Light and the Eye
• Infrared absorbed by molecular vibrations
• Ultraviolet absorbed by electrons around
atoms
• Atmosphere is transparent to visible light
• That’s why we see in this range
• Maximum solar output is green light
• Maximum eye sensitivity is green light
4. About Light
Measuring in the Sky
5. Measuring size in the sky
Size in the Sky
5. Measuring size in the sky
Angles
• 1 degree = 60 minutes (60’)
• 1 minute = 60 seconds (60”)
• Size and Distance
– A one degree object is 60 times its diameter away
(57, to be exact). 1⁰ = a quarter 5 feet away
– A one minute object is 3400 times its diameter
away . 1’ = a quarter a football field away
– A one second object is 200,000 times its diameter
away 1” = a quarter 3 miles away
5. Measuring size in the sky
Distances in Astronomy
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The Earth is 12,500 km in diameter
The Moon is 400,000 km away
The Sun is 150,000,000 km away
Pluto is 6,000,000,000 km from the Sun
Alpha Centauri is 43,000,000,000,000 km
away
• The galaxy is 1,000,000,000,000,000,000 km in
diameter
6. Astronomical Distances
Astronomical Distance Units
• The Astronomical Unit is used for planetary
distances
o 150,000,000 km = Earth-Sun distance
o Pluto is 40 A.U. from the Sun
• Light year is used for stellar distances
o Distance light travels in a year = 1013 km
o Alpha Centauri is 4.3 light years away
o Galaxy is 100,000 light years across
o Parsec (3.26 light years) is also used
6. Astronomical Distances
Light Travel Times
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Moon: 1.3 seconds
Sun: 8 minutes
Pluto: 6 hours
Nearest Star: 4.3 years
Center of Galaxy: 30,000 years
Andromeda Galaxy: 2.2 million years
Edge of visible universe: 13 billion years
6. Astronomical Distances
Telescopes
A. Refractor
B. Reflector
C. Compound (many designs)
7. How Telescopes Work
What Most People Think a
Telescope is For
7. How Telescopes Work
What Astronomers Think a
Telescope is For
7. How Telescopes Work
Surprising Facts
• Astronomers rarely look through large
telescopes visually
• Virtually all large telescopes are used solely
for photography
• Telescope time is a fiercely competitive
resource
• Modern large telescopes are $100 M +, built
by consortiums of universities and
governments
7. How Telescopes Work
Telescope Mounts
7. How Telescopes Work
All Telescopes Are Limited By The
Wave Nature of Light
7. How Telescopes Work
Bottom Line on Telescopes
• Magnification is vastly overrated
– Magnification magnifies defects in the optics and
unsteadiness in the mounting
• Images are inherently fuzzy because of the
nature of light itself
– This sets an absolute limit on magnification (rule
of thumb: 20 x diameter in cm)
– If we want detailed images of the planets, we have
to go out there physically and get them
7. How Telescopes Work
How to Use a Telescope
• The first planet you should observe is Earth
– Learn to sight and focus on familiar objects – in the
daytime – before trying to use the telescope at night
– Learn how to use all the accessories
• Things will not look like published pictures
– Objects will be small
– Objects will be faint
– Many things cannot be seen by eye even with large
telescopes
– Objects will have very subtle colors
– Objects will have low contrast
• Never look at the Sun without eye protection
7. How Telescopes Work
Saturn From Spacecraft
Saturn in Small Telescope
Hubble View of Orion Nebula
Orion Nebula in Small Telescope