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

• Visible light• Spectrum • Visible spectrum• White

• Electromagnetic radiation• Electromagnetic spectrum

= what people see= all of the types of …

=_______________

= roughly even mixture of visible spectrum

= Light= ________________

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 matter1. Gets emitted. We’ll discuss 2 ways later.– This means the object glows!

2. Gets absorbed3. Passes through (“transmitted”)4. Reflects (shiny things)5. 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?

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0 1. Emission2. Absorption3. Transmission (Passing through)4. Reflection5. Scatters

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Which does a TELEVISON do?

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0 1. Scatter2. Reflect3. Emit4. Absorb5. Transmit

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Which does a movie screen do?

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0 1. Scatter2. Reflect3. Emit4. Absorb5. Transmit

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Which happens to light when it hits my shirt?

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0 1. Scatter2. Reflect

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Which happens to light when it hits the Moon?

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0 1. Scatter2. Reflect

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What color does a green shirt ABSORB?

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0 1. Absorb all except green light2. Absorb green light

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Calif. Elementary School Science Standards for energy & seasons

• From California Science Standards, grade 3:– Students know energy comes from the Sun to Earth in the

form of light.

• And from grade 6:– 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:– 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:– 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 typesSeven types of light, in order (see page 155). Sun emits ALL

of them! See percentages below for what hits the ground.(Highest frequency smallest wavelength)

1. Gamma-rays2. X-rays3. Ultraviolet (UV) light = 3%4. Visible light = 44% (ROY G BIV)5. Infrared (IR) light = 52%6. Microwaves7. Radio waves

(Lowest frequency longest wavelength)Speed of light = (light wavelength) x (light frequency)Constant number = ONE OF THESE GOES UP, OTHER GOES DOWN

Which goes the fastest?

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0 1. Gamma rays2. Visible light3. Radio signals4. All the same

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Sunlight emission

Pictures of Sun in 6 of 7 light types

X-ray UV Visible

IR Microwave Radio

Light in your everyday life• 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

• 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?

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0 1. Radio2. Visible light3. 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 cooling1. 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:– The warming aspect instead of cooling ( = emitting IR)

For OUR solar system, that means focusing on:– 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 land-based 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

Fortunately nobody lives there! There are also precious few animal species there. How lucky!

The worst damage, by far, occurs over Antarctica.

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.

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Low-altitude ozone is _____ for Earth life.

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0 1. Good2. Bad3. 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?

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0 1. Earth would cool down2. Earth would get hotter3. 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 FactsThe 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 CO2).

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 aboutglobal 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 aboutglobal 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 & meteorologistsoMeteorologists study SHORT-term effects.

oSource: http://www.cnn.com/2009/WORLD/americas/01/19/eco.globalwarmingsurvey/index.html

IPCCIntergovernmental 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

2. China

3. Russia

4. Japan

5. IndiaBut if we separate the US into states…

1. China

2. Russia

3. Japan

4. IndiaAnd 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

5. India – 1.8 tons

Driving 12,000 miles releases ~6 tons CO2.

(average;Prius is ~2.5 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

Bottom line: Most scientists predict several degreesof additional warming during the coming century,mostly caused by human emissions.

• 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.

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?

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0 1. Yes2. 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?

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0 1. Redshift2. Blueshift

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Redshift & blueshift

• 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.