Light & Earth’s atmosphere
Chapters 5 and 10
(Hints of chapter 2, more later)
Learning Outcomes, Objectives, & Goals
• Appreciating science in general, and astronomy in specific.
• Understanding how knowledge is gained and be critical of what you
see and hear.
• Developing a working knowledge of the scientific method and how to
apply it to real world situations.
• Critically analyzing and evaluating information, scientific or
otherwise
• Learn some simple astronomical nomenclature/terminology.
• Develop a sense of what scientists know about the overall universe,
its constituents, and our location
• Explain how electromagnetic radiation is used to reveal the
properties of stars and planets.
Student Learning Outcomes
• Understand the major properties of light, including
wave and particle properties.
• Know the 7 types of light and the order of the major
wave & particle properties for these types.
• Understand how light and matter interact, in both
distant and everyday objects. (Including Doppler
effect.)
• Understand the nature of light properties and its
relationship to the ozone hole and why this is a
problem.
• Understand the nature of light properties and its
relationship to global warming. Know the major
manmade causes of global warming.
Fancy words
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Visible light = what people see
Spectrum
= all of the types of …
Visible spectrum =_______________
White
= roughly even mixture of visible
spectrum
• Electromagnetic radiation = Light
• Electromagnetic spectrum = ________________
Wave (Light) properties
• NEXT LINE IS IN BOTTOM OF THIS SLIDE ON YOUR
NOTES:
• Amplitude = strength of wave.
• Wavelength – see page 149
• Frequency – How often a wave passes by
– units are: waves per second = Hertz (Hz)
• Speed = how fast one wave pattern moves
– miles/hour
– Wave speed = (wavelength) x (wave frequency)
5 ways light interacts with matter
1. Gets emitted. We’ll discuss 2 ways later.
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2.
3.
4.
5.
This means the object glows!
Gets absorbed
Passes through (“transmitted”)
Reflects (shiny things)
Scatters in many directions (most things)
Textbook combines “reflect” & “scatter” together.
See figures 5.2 & 5.3 on pages 151-152.
Why is the sky blue? Scattering! See pages 304-305
(not on your test)
Which one of these 5 interactions
causes damage to cells?
1.
2.
3.
4.
5.
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Emission
Absorption
Transmission (Passing through)
Reflection
Scatters
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Which does a TELEVISON do?
1.
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Scatter
Reflect
Emit
Absorb
Transmit
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Which does a movie screen do?
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Scatter
Reflect
Emit
Absorb
Transmit
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Which happens to light when it hits my
shirt?
1. Scatter
2. Reflect
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Which happens to light when it hits the
Moon?
1. Scatter
2. Reflect
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What color does a green shirt ABSORB?
1. Absorb all except green light
2. Absorb green light
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Calif. Elementary School Science Standards
for energy & seasons
•
From California Science Standards, grade 3:
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And from grade 6:
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Students know energy comes from the Sun to Earth in the
form of light.
Students know solar energy reaches Earth
through radiation, mostly in the form of visible
light.
And from grade 7:
–
Students know visible light is a small band within a
very broad electromagnetic spectrum.
Calif. Science Standards for light
•
From California Science Standards, grade 3:
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Students know the color of light striking an
object affects the way the object is seen.
Students know an object is seen when light
traveling from the object enters the eye.
And from grade 7:
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Students know that for an object to be seen,
light emitted by or scattered from it must
be detected by the eye.
Students know light travels in straight lines if
the medium it travels through does not change.
Students know that white light is a mixture of
many wavelengths (colors) …
Students know light can be reflected,
refracted, transmitted, and absorbed by
matter.
Planet temperature
Depends on two things:
1. Amount of energy absorbed (warm up)
2. Amount of energy emitted (cool off / down)
Light types
Seven types of light, in order (see page 155). Sun emits ALL
of them! See percentages below for what hits the ground.
(Highest frequency
1.
2.
3.
4.
5.
6.
7.
smallest wavelength)
Gamma-rays
X-rays
Ultraviolet (UV) light = 3%
Visible light = 44% (ROY G BIV)
Infrared (IR) light = 52%
Microwaves
Radio waves
(Lowest frequency
Speed of light
Constant number
longest wavelength)
= (light wavelength) x (light frequency)
= ONE OF THESE GOES UP, OTHER GOES DOWN
Which goes the fastest?
1.
2.
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Gamma rays
Visible light
Radio signals
All the same
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Sunlight emission
Pictures of Sun in 6 of 7 light types
X-ray
IR
UV
Visible
Microwave
Radio
Light in your everyday life
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Your eyes see ___________ light.
When ________ light lands on your skin, skin gets warmer.
When ________ light lands on your skin, skin is damaged.
When ________ light lands on your skin, you get radiation
poisoning. (two answers)
• When ________ light lands on your skin, nothing changes
unless a LOT lands on you. (two answers)
• Digital cameras see visible AND infrared light. Remote
controls often use IR light. Look: cell phone + remote
• Blacklights emit UV light.
– Take a look – Moon lights, portable UV lights, blacklights.
Light acting as a particle
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Light acts like a wave.
Light also acts like a particle.
Light particles are called ….
What are the 7 types of light?
They differ in wavelength, frequency, and
energy in a photon.
Which kind of light has a longer
wavelength?
1. Radio
2. Visible light
3. Gamma rays
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Photons and humans
• Which type of photon carries the most
energy?
• Which kind is most dangerous?
• Least dangerous?
Sources of cooling
1. Emitting light
– Which kind of light does the Sun shine most?
– Objects colder than stars cool mostly by shining away
infrared light. (See page 168 – Wien’s law)
– Colder objects also give off less light (Stefan’s law, p.
168)
– Are you hotter or colder than a star?
What kind of light do you emit to cool off? Let’s look.
2. Other cooling methods inside planets
– Similarly, can ignore these again
For the rest of this course, we’ll focus on:
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The warming aspect instead of cooling ( = emitting IR)
For OUR solar system, that means focusing on:
–
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Absorbing Visible Light. Why visible light?
Which other type of light should we focus on?
Using light to identify properties
• Objects can emit light in two ways:
1. Because they’re hot
– These give off ALL kinds, but one form more than others.
– Examples: the Sun, incandescent light bulbs
– Which kind given off most by Sun? Light bulbs?
• Peak light indicates temperature.
2. Because they are fluorescent
– These give off ______________ (we’ll see)
•
Called “spectral lines” or “emission lines”
– Example: fluorescent gas tubes we’ll see
– Useful to astronomers because __________
___________________________________
– Show animation: Composition of Mystery Gas [4th row from bottom]
Light wave properties & human
influences
• Now that you understand the basics of light
properties, let’s examine two issues related to
humans and the Earth.
The Ozone Layer
• Ozone is a form of molecular oxygen, O3.
• Occurs naturally (if the atmosphere already has O2) in the upper
atmosphere in small quantities (parts per trillion).
•Absorbs high-energy UV photons from the Sun very efficiently
(90-99% of them).
• Without it, UV photons reach the surface and kill most landbased life.
•People would receive a lethal dose within a minute or two.
• Chloro-Fluoro-Carbons (CFCs) produced by humans are nearly
inert molecules that get into the upper atmosphere.
• CFCs attack the ozone molecules. Each CFC molecule destroys
thousands of ozone molecules over its several year lifetime before
the CFC molecule is finally destroyed. (No convection in upper
atmosphere. See pages 305, 324-325.)
Ozone Hole over Antarctica
The worst damage, by far, occurs
over Antarctica.
Fortunately nobody lives there!
There are also precious few
animal species there. How
lucky!
Equally fortunate is that we found this problem and its cause in
time! Here is a more recent map of the ozone layer. It’s not as good as we’d hoped.
CFCs in our atmosphere
Production of CFCs were banned worldwide in 1988. Look at the chart after
1990. CFCs are dropping! Predictions were that the worst damage to the
ozone layer would occur by 2000, and then it would start “healing”. BUT: in
2007, the hole got bigger. Hopefully the healing will (re-?)start soon!
EXPECTED TO BE BACK TO NORMAL LEVELS IN 2065-2070.
Important point: international effort was necessary and seems to be working.
Human influences & economics
• Until recently, people assumed we couldn’t affect
the atmosphere.
• Then we started measuring it.
• Ozone hole showed up. Nobody expected it.
• It cost a LOT of money to stop damaging the ozone
layer.
• It was money we HAD to spend to keep life alive.
Human influences & economics
• People didn’t believe the ozone hole was caused by
humans. They claimed:
– FIRST: It’s not happening
– SECOND: It might be natural; Earth goes through cycles.
• We’re not making enough stuff to cause the damage.
– NOW:
• We don’t know enough (it’s too early) to make any major changes
• It might naturally fix itself; life has been on Earth for billions of years. It’ll
adapt and solve this problem.
• The economy would suffer if we force ourselves to change our ways
• Same argument used for cigarettes & lung cancer, seat belts, airbags, car
catalytic converters, and sulfur dioxide emissions (that cause acid rain).
Using same argument now to prevent increasing fuel economy. History
shows these economic arguments were often wrong.
• These EXACT same arguments are now being used when
discussing global warming.
High-altitude ozone is _____ for
Earth life.
1. Good
2. Bad
3. Not important
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Low-altitude ozone is _____ for
Earth life.
1. Good
2. Bad
3. Not important
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New topic coming up. First I get your
thoughts.
What would happen if we wrapped the
Earth in a visible-light transparent but
infra-red blocking substance? Talk to
your neighbor. I’ll solicit answers from
you.
What would happen IN THE LONG TERM if we
wrapped the Earth in an infra-red blocking
substance?
1. Earth would cool down
2. Earth would get hotter
3. Earth would stay same
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Global Warming
• The fundamental idea about global warming
and the potential dangers deals with the
human-caused portion of Earth’s Greenhouse
Effect.
Greenhouse effect
• Did we use the infrared camera?
• Did we see people wearing glasses on the infrared
camera?
• What did that mean?
• What happens when you surround Earth with an IR
blocking gas?
• This is called the Greenhouse effect.
• Two key ideas:
– Visible light from Sun comes in, warming Earth up
– Infrared light from Earth gets blocked by some
Greenhouse agent, so Earth can’t cool as easily
Greenhouse Agents and effects
• Some gases are greenhouse agents
– Natural gas (methane = CH4) is one of the best.
– CO2 is a good one. (methane is 23x better!)
– H2O is a weak one. But lots of it in Earth’s atmosphere, which
causes most of our Greenhouse Effect.
• Greenhouse atmosphere acts like a blanket.
• Earth would be 31 ˚C colder than it is without G.E.!
– Water would freeze! (Avg temp: 3 ˚F or -16 ˚C)
• Which planet do you think should be hottest?
– Why?
• Does Venus have an atmosphere?
• Why is Venus hotter than Mercury?
From James Hansen’s PowerPoint downloaded from his NASA –Goddard web page. The next
slide’s graphs are from an article he wrote a few years ago. This graph was SET to zero for a
specific year. The century-long change is the important idea here.
Global Warming – The Facts
The temperature of the Earth is clearly
rising (middle graph).
We see: average temperature of Earth
has increased about 0.5 ˚C = 0.9 ˚F in the
past 30 years. This is much faster than
scientists can explain without human
influence.
Coincides with huge increase in CO2
from burning fossil fuels. Levels now
higher than any level seen in past
400,000 years and rising. (Was 280 ppm in
1850; in 2009 it’s 387 & rising 2.4/yr. In 1980’s rose
1.4 ppm/yr, <1ppm/yr before then)
Other changes: sea level has risen,
carbonation in the oceans increased (i.e.
oceans are storing much of our CO ).
Global Warming – related facts
• People make lots of CO2 and CH4 since industrial revolution.
• Both of these gases cause the Greenhouse effect.
•Most from the USA & China burning fossil fuels. Largest CO2
emitters. (But China has 4x the US population! Use LOTS of coal!)
•Cutting down/burning trees (deforestation) is also a major factor.
• Do we understand EVERYTHING about the temp increase?
•Of course not. Atmosphere = complicated. New data every day.
Your book gives an objective summary on pages 328-330.
NOTE: While humans account for 2 percent of the world’s carbon
dioxide emissions. That’s enough to tip the balance, though.
Global warming IS NOT RELATED TO THE OZONE LAYER.
What people think about
global warming – part 1
You’ve probably heard about the “controversy”
surrounding global warming.
Here are facts:
1.EVERYONE who understands the data agrees that
the Earth’s temperature is rising. 100% of scientists
agree the temperature is rising in the long term
(over many decades).
2.The only “controversy” was WHAT IS CAUSING the
temperature to rise.
What people think about
global warming – part 2
o Most (97% of) scientists who study the Earth’s
LONG-term atmosphere believe manmade CO2 is
the biggest cause.
o Even 90% of ALL 3,146 earth scientists surveyed
agreed temperatures are rising, and 82% said
“human activity [has] been a significant factor…”
o However, some deniers say that we don’t know
enough yet to say what’s going on.
oMostly petroleum geologists & meteorologists
oMeteorologists study SHORT-term effects.
oSource: http://www.cnn.com/2009/WORLD/americas/01/19/eco.globalwarmingsurvey/index.html
IPCC
Intergovernmental Panel on Climate Change
• IPCC = group of ~2000 atmospheric scientists
• IPCC’s 4th report (2007):
• Greenhouse gas emission rate has increased 70% since
1970.
• “Warming of the climate system is unequivocal.”
• 90% likelihood that human activity is affecting the climate.
• Under current policies, emission will continue to increase
for decades to come.
If we continue to do what we are doing now, we are in
deep trouble. - Ogunlade Davidson, IPCC
Five Biggest CO2 emitters (as of 2004)
1. United States
1. China
2. China
2. Russia
3. Russia
3. Japan
4. Japan
4. India
5. India
But if we separate the US into states…
And my personal favorite:
5. Texas
… 12. California
China has now (in 2008) overtaken the US in
total CO2.
Five Biggest CO2 emitters PER PERSON (as of
June 2008)
1. USA – 19.4 tons per year
2. Russia – 11.8 tons
3. European Union – 8.6 tons
4. China – 5.1 tons
Driving 12,000
miles releases ~6
tons CO2.
(average;
Prius is ~2.5 tons)
5. India – 1.8 tons
China’s rate is growing faster than the US, largely due
to coal and cement plants. But they have a lot of
catching up to do.
Other possible causes of global warming
• Other things may explain the temp raise during the last 100
years.
•Natural temp increase.
(This is the most believable alternative.)
•Sunspot activity (Maunder Minimum). Less sunspots =
colder Earth. Not well understood. But possible link.
•We thought this is the strongest sunspot cycles during
the last 50 years. But as of Apr 2009 we may be in the
deepest solar minimum in 100 years, so this argument is
less convincing. Stay tuned as we learn more.
Bottom line: Most scientists predict several degrees
of additional warming during the coming century,
mostly caused by human emissions.
Consequences of global warming
• Retreat of glaciers (Apparently happening)
• Melting of Greenland & Antarctic ice caps. (Seen;
Greenland’s caps are melting faster than predicted)
• Melting of Arctic permafrost.
• Melting of Arctic sea ice.
• Rising sea level & flooding on coasts.
• Stronger hurricanes/storms (a bit more controversial)
• Shift of malaria farther from equator. (Seen already)
• Similar shift of wine-producing regions. (Seen)
• Similar shift of desert belt.
• Mass extinctions of wildlife.
Did Al Gore get the “science of global
warming” right?
1. Yes
2. No
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Doppler Effect – what is it?
• Sound maker demo
– Close eyes & listen; describe
– 440 Hz. F#
– Match description with observation
Which kind of Doppler shift do we see for
most objects in the universe?
1. Redshift
2. Blueshift
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Redshift & blueshift
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Interactive figure 5.22
Why called redshift & blueshift for light.
Doppler shift of lines [5th row top]
Application in your everyday (?) life:
– Speeding tickets!
Learning Outcomes, Objectives, & Goals
• Appreciating science in general, and astronomy in specific.
• Understanding how knowledge is gained and be critical of what you
see and hear.
• Developing a working knowledge of the scientific method and how to
apply it to real world situations.
• Critically analyzing and evaluating information, scientific or
otherwise
• Learn some simple astronomical nomenclature/terminology.
• Develop a sense of what scientists know about the overall universe,
its constituents, and our location
• Explain how electromagnetic radiation is used to reveal the
properties of stars and planets.