Seasons, Light, and Human effects on Earth

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Seasons, Light, and Human effects on Earth

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Title: Seasons, Light, and Human effects on Earth

1
Seasons, Light, andHuman effects on Earths
atmosphere

When why is it hot and cold - Section 2.2
Light parts of chapter 5 (see study guide)
Earths atmosphere parts of chapter 10 (see
study guide)

2
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/termin
ology.
Develop a sense of what scientists know about
the overall universe, its constituents, and our
location
Explain the causes of seasonal variations in the
length of the day, the direction of sunrise and
sunset, and the amount of solar heating.
Explain how electromagnetic radiation is used to
reveal the properties of stars and planets.

3
Overarching questions

What causes it to be hot and cold?
What things could cause temperature differences?
What causes Earth summer / winter?
How is the Earths tilt related to seasons, if at
all?
What info would you need to know to predict
seasons on other planets?
What is precession?

4
Planet temperature

Depends on two things
Amount of energy absorbed (warm up)
Amount of energy emitted (cool off / down)

5
Sources of warming for planets

Sunlight warms the outside of planet
Seven types of light, in order (see page 155)
Gamma-rays
X-rays
Ultraviolet (UV) light 10
Visible light 45 (ROY G BIV)
Infrared (IR) light 35
Microwaves
Radio waves
Energy source from inside warms interior
VERY small. Dont affect Earth noticeably.

6
Wave (Light) properties

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)
Amplitude strength of wave.

7
Revisiting the light types

Seven types of light, in order (see page 155)
(Highest frequency smallest wavelength)
Gamma-rays
X-rays
Ultraviolet (UV) light 10
Visible light 45 (ROY G BIV)
Infrared (IR) light 35
Microwaves
Radio waves
(Lowest frequency longest wavelength)

Speed of light (light wavelength) x
(light frequency) Constant number ONE OF
THESE GOES UP, OTHER GOES DOWN
8
Light in your everyday life

Your eyes see ___________ light.
When ________ light lands on your skin, your skin
gets warmer.
When ________ light lands on your skin, you get
skin damage.
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

9
Using light to identify composition

Objects can emit light in two ways
Because theyre 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?
Because they are fluorescent
These give off ______________ (well see)
Called spectral lines or emission lines
Example fluorescent gas tubes well see
Useful to astronomers because __________
___________________________________

10
5 ways light interacts with matter

Gets emitted. Well discuss 2 ways later.
Gets absorbed
Passes through (transmitted)
Reflects (shiny things)
Scatters in many directions (most things)
See figures 5.2 5.3 on pages 151-152.

11
Which happens to light when it hits my shirt?

Scatter
Reflect

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12
Which happens to light when it hits the Moon?

Scatter
Reflect

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13
What color does a green shirt ABSORB?

Absorb all except green light
Absorb green light

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14
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.

15
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.

16
Sources of cooling

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 Wiens law)
Colder objects also give off less light (Stefans
law, p. 168)
Other cooling methods inside planets
Similarly, can ignore these again
For the rest of this course, well focus on
The warming aspect.
For OUR solar system, that means focusing on
Absorbing Visible Light. Why visible light?

17
More light in everyday life - invisible

What kind of light does your body mostly emit
(give off)?
Want to see it?
Neat fact Blacklights emit some UV. Take a look.

18
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.)

19
Ozone Hole 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. Its not as good as wed
hoped.
20
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.
21
Human influences economics

Until recently, people assumed we couldnt 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.

22
Human influences economics

People didnt believe the ozone hole was caused
by humans. They claimed
FIRST Its not happening.
SECOND It might be natural Earth goes through
cycles.
Were not making enough stuff to cause the
damage.
NOW
It might naturally fix itself life has been on
Earth for billions of years. Itll adapt and
solve this problem.
The economy would suffer if we force ourselves to
change our ways
Same argument used for seat belts, airbags,
catalytic converters in cars, 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.

23
New topic coming up. First I get your thoughts.
24
What would happen if we wrapped the Earth in an
infra-red blocking substance? Talk to your
neighbor. Ill solicit answers from you.
25
What would happen if we wrapped the Earth in an
infra-red blocking substance? Talk to your
neighbor. Ill solicit answers from you.

Earth would cool down
Earth would get hotter
Earth would stay same

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26
Global Warming

The fundamental idea about global warming and the
potential dangers deals with the human-caused
portion of Earths Greenhouse Effect.

27
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 cant cool as easily

28
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 Earths
atmosphere, which causes most of our Greenhouse
Effect.
Greenhouse atmosphere acts like a blanket.
Why is Venus so hot?
Earth would be 31 C colder than it is without
G.E.!
Water would freeze! (Avg temp 3 F or -16 C)

29
From James Hansens PowerPoint downloaded from
his NASA Goddard web page. The next slides
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.
30
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 30-50 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 its 387 rising
2.4/yr. In 1980s rose 1.4 ppm/yr, lt1ppm/yr
before then) Other changes sea level has risen,
carbonation in the oceans increased (i.e. oceans
are storing much of our CO2).
31
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
worlds carbon dioxide emissions. Thats enough
to tip the balance, though.

Global warming IS NOT RELATED TO THE OZONE LAYER.
32
What people think aboutglobal warming

Most (97 of) scientists who study the Earths
LONG-term atmosphere believe manmade CO2 is the
biggest cause.
Even 90 of ALL 3,146 earth scientists surveyed
agreed temperatures are rising, and 82 said
human activity has been a significant factor
However, some deniers say that we dont know
enough yet to say whats going on.
Mostly petroleum geologists meteorologists
Meteorologists study SHORT-term effects.
Source http//www.cnn.com/2009/WORLD/americas/01/
19/eco.globalwarmingsurvey/index.html

33
IPCCIntergovernmental Panel on Climate Change

IPCC group of 2000 atmospheric scientists
IPCCs 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
34
Five Biggest CO2 emitters (as of 2004)

United States
China
Russia
Japan
India

China
Russia
Japan
India
And my personal favorite
5. Texas
12. California

But if we separate the US into states
China has now (in 2008) overtaken the US in total
CO2.
35
Five Biggest CO2 emitters PER PERSON (as of June
2008)

USA 19.4 tons per year
Russia 11.8 tons
European Union 8.6 tons
China 5.1 tons
India 1.8 tons

Driving 12,000 miles releases 6 tons
CO2. (averagePrius is 2.5 tons)
Chinas rate is growing faster than the US,
largely due to coal and cement plants. But they
have a lot of catching up to do.
36
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.

Bottom line Most scientists predict several
degrees of additional warming during the coming
century, mostly caused by human emissions.
37
Consequences of global warming

Retreat of glaciers (Apparently happening)
Melting of Greenland Antarctic ice caps. (Seen
Greenlands 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.

38
Did Al Gore get the science of global warming
right?

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39
Back to seasons

More than you ever thought youd know about the 7
different types of light.
Back to seasons and why its hot and cold at
different times and in different months.

40
Absorption of visible light

Which absorbs more sunlight? Air or water/ground?
How do you know?
Things that affect amount of light absorbed
Distance to Sun
Color of ground (black vs. white)
Look at the map on page 40. Which is better at
absorbing light - Water or ground? Clicker
(technical note IR color is important too.
Why?)
We wont talk about color anymore. Climate models
need to account for it we dont.
Exposure time in sunlight (daytime length)

41
Which is better at absorbing visible sunlight?
(see picture on p 40 first)

Water
Ground

After finishing this slide, finish the previous
slide.
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42
Distance

Many people think seasons are caused by the
distance to the Sun.
Were good scientists now, so what should we do?
Lets test this idea!
BESIDES temperature, predict an observation we
could make from Earth associated with the
distance to the Sun
Predict what we would observe.
The Sun will look bigger during _______ and .
Write your prediction down in a place you can
cover up. Again, leave a place for the correct
answer that you can cover up.

43
Movie coming soon to web page
44
Distance to Sun

Closest to Sun perihelion
January 3
Furthest from Sun aphelion
July 4
On EARTH, difference between nearest and furthest
is small (3.4)
(3 million miles or 5 million km)
Only noticeable using careful pictures. Not
without.
Compare that to the size of the entire Earth
Radius of Earth is ___________.
Lecture tutorial, pages 91-92. Tell them answer
to 3.

45
Who did you agree with on the bottom of page 92?

Student 1
Student 2
Both
Neither

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46
Time absorbing visible light

Is it true that there is MORE time to absorb
visible sunlight during SUMMER? Why?
Is it true that there is LESS time to absorb
visible sunlight during WINTER? Why?
At night, is the Earth heating up or cooling off?
How?
Does the cooling time difference strengthen or
weaken the idea that summer is hot because of
longer days?
Well focus on daytime from now on. Nighttime
arguments yield the same results.

47
Daytime length

Our next question
Why are daytime and nighttime lengths different
at different places?

48
Times on a non-tilted Earth
Label your Earth with NP, SP, equator.
Shade the night side of your Earth appropriately.
Sun is far away to the left
Noon is EVERYWHERE on the left, north pole to
south pole Midnight is EVERYWHERE on the right,
north pole to south pole
49
Daytime Nighttime on a non-tilted Earth
Label your Earth with NP, SP, equator.
Shade the night side of your Earth appropriately.
Sun is far away to the left
Where will the following places be after 12 hours
(half a rotation?)
Each location travels across the Earth as the
Earth spins. How much time does person A spend in
the Sun? Person B? Person C?
50
The actual Earth is tilted. How much? Heres how
we would draw that.
Sun is ________ Copy this into your notes.
DONT DRAW THE NEXT PART YET Lets see an
un-tilted Earth
Now draw NP, SP, equator for your notes We could
have tilted the Earth to the left, if looking
from the other side. On this tilted Earth, which
direction to the Sun?
Noon on the left, pole-to-pole (purple) Midnight
on the right, pole-to-pole (turquoise)
51
How do places move as the tilted world turns?
Here is the midnight side
Copy a right-tilted Earth into your notes. Here
is the noon side. Where will the following places
move during the next 12 hours? Draw arrows to
show their path.
How much time does person A have in Sun? Does
person B spend more time in the day or more time
at night? Which gets the LEAST time in the Sun?
A, B, or C?
How much sunlight does person D get on this
date? Where is the cut-off? The name for this
place is . Draw a cutoff for the antarctic
circle. Northern hemisphere longer days or
nights? South?
The date shown is December 21.
Which season for the north? South?
52
Daytime / nighttime seasons, part 2

It appears we have a good explanation. Our
temperature observations are explained.
We see north south seasons are opposite, also.
The CAUSE of different times tilt of Earth. You
may already have heard the tilt causes the
seasons.
Before we draw our conclusion, a good scientist
will do what to their newly considered
hypothesis?
Test it!
Is there anyplace on Earth that gets prolonged
sunlight during some part of its year?
Whats the temperature like there?
Is the daytime length the only important effect
for hot/cold?
It is important for us. But its not the MOST
important thing for hot vs. cold
or for summer vs. winter!

53
Season causes whats dominant?

So, weve ruled EVERYTHING out as the dominant
effect!?!?!
Earth-Sun Distance is backwards for people in
US
Earths color doesnt change much month-to-month
Daytime / nighttime doesnt explain tropical
polar weather at any time of year, but
it partly explains hot summer / cold winters for
middle-latitudes.
RECALL the different day/night times were
caused by
Obviously weve missed something if we want a
complete picture why its hot and cold at
different places at different times.
Lets observe carefully as we travel to other
parts of the world during different seasons.
Lets look at the Sun from the north pole, LA,
and the equator. demo
Aside from always being up, what do we notice
about Santas Sun?
In LA, how is that different?

54
California Elementary School Science Standards
for seasons

From California Science Standards, grade 3
Students know the position of the Sun in the sky
changes during the course of the day and from
season to season.
Students know the patterns of stars stay the
same, although they appear to move across the sky
nightly, and different stars can be seen in
different seasons.

55
Sun location temperature

Why does Sun location affect the amount of
sunlight we absorb? Lets examine
Imagine a light bulb in the center of the room
your paper ground. Make your ground catch the
most sunlight.
Standing on this ground, which direction is the
Sun?
Conclusion
When the Sun is high in the sky, the ground faces
the Sun!
Is this going to be a big effect or small effect?
Why?
Work on Lecture Tutorial, page 93 ONLY

56
When is the Sun directly overhead here in LA?

Every day at noon
Only during summer
Never

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57
Sun is far away to the left
Shade your Earth appropriately.
Is ground A directly facing the Sun? Is the Sun
high in the sky, midway, or low? Will ground A be
hot, medium, or cold? Is ground B directly facing
the Sun? Is the Sun high in the sky, midway, or
low? Will ground B be hot, medium, or cold? Put a
dot on the ground directly facing the Sun What
would weather be like there? Lets add the
Earths tilt. Should you move the dot after
tilting? (Clicker) Which is hotter, C or the
equator? Which hemisphere is hotter north or
south? (Clicker)
Earth
58
Should you move the dot on your drawing now that
youve added the tilt?

North
South
Cannot be determined

Yes
No
Cannot be determined

Its still called summer for the ENTIRE
hemisphere, even though some places are cold.
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61
Two pictures

The next two slides show how the Earths orbit
looks on 2 important dates.

62
Looking from one side
Where is the Sun directly overhead in this
drawing? Name __________ Draw path over 12 hours
NEIGHBOR On this left-side drawing, which
hemisphere has summer? How can you tell?
Copy this drawing into your notes
Where is the Sun directly overhead in this
drawing? Name __________ Draw path over 12 hours.
NEIGHBOR On this drawing, which hemisphere has
summer? How can you tell?
This date is June 21
This date is Dec 21
63
Tropics
Where is the Sun directly overhead in between
June 21 and December 21? Where do you have to
live to see the Sun straight overhead?
64
Opposite perspective version

Viewing from the back side, looking towards us,
youd see the next drawing.
This next drawing is the version used in Lecture
Tutorial, page 94.

65
Looking from the other side
Copy this drawing into your notes also
This date is June 21
Notice in both cases Tilts are both in same
direction Dates _____________! On left drawing,
which hemisphere is summer? On right?
This date is Dec 21
If this picture were to scale, this right drawing
would be a tiny bit further away from the Sun
than the left drawing.
If this picture were to scale, the north in THIS
side is CLOSER(!) than the north on the right
side drawing!
66
Lecture Tutorial

Work on Pages 94-96 for practice.

67
What season is it for D at noon?

Summer
Winter
Spring
Fall
Cannot be determined

Summer
Winter
Spring
Fall
Cannot be determined

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69
Season start dates what happens
You should be able to convince yourself that the
seasons are opposite in the northern southern
hemispheres. You should also understand why.

June 21 (6/21) solstice. In LA summer
solstice. How about in Australia?
First official day of summer (in north)
Where is the Sun straight up?
What happens inside the Arctic circle? Antarctic
circle?
Dec 21 solstice. In LA winter solstice. How
about in Australia?
First official day of winter (in north)
Where is the Sun straight up?
What happens inside the Arctic circle? Antarctic
circle?

March 21 equinox. In LA Spring. (Vernal
equinox)
First official day of spring (in north)
Where is the Sun straight up?
Why do you think its called an equi-nox?
September 21 equinox. In LA Fall (Autumnal
equinox).
First official day of fall (in north)
Where is the Sun straight up?
Why do you think its called an equi-nox?

See also pages 38-39
70
Which day of the year should the equator be
hottest?

June 21
Dec 21
March 21
Sep 21
Both equinoxes
Both solstices

E
G
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72
Which letter is hottest at noon?
C
B
D

A
E
G
F
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73
Which letter is hottest at noon?
B
D

Hot
Cold

B
C
D
C
B
B
D
D
A
A
day
H
H
E
E
E
G
G
G
F
F
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75
What season is it for the letter shown in figure
__ below?

Summer
Winter
Cannot be determined

March 21
June 21
Sep 21
Dec 21

A
H
E
G
F
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77
Which location is hotter at noon?

A
B
Same
Cannot be determined

A
B
Same
Cannot be determined

But just in case
Try the Seasons Ranking Tasks handout for
HOMEWORK (outside of class).

80
Precession
See pages 41-42 in textbook for this
topic. Youve probably noticed that the sky has
changed a little over the last 2000 years.
(Birthday game) The ancients knew about this, but
it did take several hundred years of observations
to figure it out. As weve discussed before, the
Earths rotation axis is tilted 23.5 away from
its revolution axis around the Sun. The amount of
this tilt doesnt change. The direction of this
tilt, however, does. It wobbles in a circle once
every 26,000 years. A more exact number is
25,771.5 years. Over 2000 yrs this slow wobble
causes a slight change in the zodiac
constellations. This is why your sign is
probably 1 sign earlier. Precession has NOTHING
TO DO WITH SEASONS. Precession 26,000 yr
cycle!Seasons 1 yr cycle!
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Whats Your Sign? Then Now
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Overarching questions