Seasons

When & why is it hot and cold

Section 2.2

Overarching questions

• What causes it to be hot and cold?• What things could cause temperature

differences?• What causes Earth summer / winter?• How is the Earth’s tilt related to seasons, if

at all?• What info would you need to know to

predict “seasons” on other planets?• What is precession?

Planet temperature

Depends on two things:

1. ___________________________________

2. ___________________________________

Sources of warming for planets

• _________________Seven types of _______, ________ (see page ____)

1. ____________________

2. ____________________

3. ____________________

4. ____________________

5. ____________________

6. ____________________

7. ____________________

• Energy source from inside (later in semester)VERY small. Don’t affect Earth noticeably.

Sources of cooling

1. ______________________– Objects colder than stars cool mostly by _________

_________________________________________– What would happen if we wrapped the Earth in an

______________________________________?2. Other cooling methods inside planets

– Similarly, can ignore these again

For the rest of this topic, we’ll focus on:– ____________________________________.

For planets in OUR solar system, that means focusing on:

– ________________________. Why _______ light?

Absorption of visible light

Which absorbs more sunlight? Air or water/ground? How do you know?

Things that affect amount of light absorbed:1. _____________________ 2. _____________________________

– 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 won’t talk about color anymore. Climate models need to account for it; we don’t.

3. ___________________________________

DistanceMany people think seasons are caused by the

distance to the Sun.

We’re good scientists now, so what should we do?

Let’s __________________!• 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 ____________ 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.

Movie – coming soon to web page

Distance to Sun

• Closest to Sun = ____________________– _________________

• Furthest from Sun = __________________– ________________________

• On EARTH, difference between nearest and furthest is _________________________

(__________ miles or ______________ km)– ________________________________ Not without.

• Compare that to the size of the entire Earth:Radius of Earth is ___________.

Lecture tutorial, pages 91-92

Time absorbing visible light

• Is it true that there is __________________ _____________________________? Why?

• Is it true that there is __________________ _____________________________? Why?

• At night, is the Earth heating or cooling? How?

• Does the cooling time difference strengthen or weaken the idea that summer is hot because of longer days?

Daytime length

• Why are daytime and nighttime lengths different at different places?

Daytime & Nighttime on a non-tilted Earth

Where will the following places be after 12 hours (half a rotation?)

Anoon

Bnoon

Cnoon

Dnoon

Each location _____________ ________________________.

How much time does person A spend in the Sun?

Person B?

Person C?

Sun is far away to the left Shade your Sun appropriately.

The actual ___________________.

How much?

Here’s how we would draw that.

Now draw NP, SP, equator for your notes

We could have tilted the Earth _________________________

______________________.

On this tilted Earth, which direction to the Sun?

Sun is ________

Copy this into your

notes.

How do places move as the tilted world turns?Copy a “right-tilted” Earth into your notes.

Where will the following places move during the next 12 hours? Draw arrows to show their path.

Cnoon

Dnoon

Bnoon

AnoonHow 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 ____________________.

Northern hemisphere – longer days or nights?

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?

The date shown is ____________________

Which season for the north?

Daytime / nighttime & seasons, part 2It appears we have a good explanation. Our temperature observations are

explained.We see _____________________________________________, also._______________________________________. 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?

• ____________________________________• Is there anyplace on Earth that gets __________________________

______________________________________________________• What’s the temperature like there?• Is the daytime length the only important effect for hot/cold?• _____________________________. But _____________________

_______________________________________________________!

Season causes – what’s dominant?So, we’ve ____________________________ as the dominant effect!?!?!1. Earth-Sun _________________________ for people in US2. Earth’s ___________________________ month-to-month3. _________________ doesn’t explain _________________________

at any time of year, but …___________________________________________________.RECALL: the different day/night times were caused by …

Obviously we’ve missed something if we want a complete picture – why it’s hot and cold at different places at different times….

Let’s observe carefully as we travel to other parts of the world during different seasons.

Let’s look at the Sun from the north pole, LA, and the equator. *demo*• Aside from “always” being up, what do we notice about Santa’s

Sun?• In LA, how is that different?

Sun location & temperatureWhy does Sun location affect the amount of sunlight we

absorb? Let’s 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 __________________________________________!

• Is this going to be a big effect or small effect? Why?

Work on Lecture Tutorial, page 93 ONLY

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?

Where is the ground directly facing the Sun?What would weather be like there?Let’s add the Earth’s tilt.Does that change the hottest place? (Clicker)Which is hotter, C or the equator?Which hemisphere is hotter: north or south? (Clicker)

Earth

Sun is _________________

shade your drawing appropriately

AB

Ask your neighbor: Which hemisphere is hotter?

0

0

0 1. North

2. South

3. Cannot be determined

23°

23°

23°

23°nightday

Earth

NP

SP

Equator

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

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61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80

Two pictures

• The next two slides show how the Earth’s orbit looks on 2 important dates.

This date is __________

This date is ________

Sun

Looking from one sideNEIGHBOR: On this drawing, which hemisphere has summer? How can you tell?

NEIGHBOR: On this drawing, which hemisphere has summer? How can you tell?

Copy this drawing into your notes

___________________ version

• ___________________________, looking towards us, you’d see the next drawing.

• This next drawing is the version used in Lecture Tutorial, page 94.

This date is _______This date is ________

Sun

Looking from the other side

________________________

________________________

__________________! On left drawing, which hemisphere is summer? On right?

Copy this drawing into your notes also

Lecture Tutorial

• Work on Pages 94-96.

• 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 = __________. In LA = ____________. How about in Australia?– ________________________ (in north)– Where is the Sun straight up?– What happens inside the Arctic circle? Antarctic circle?

• ___________________. In LA = _____. (Vernal ________)– _________________________ (in north)– Where is the Sun straight up?– Why do you think it’s called an equi-nox?

• ______________________. In LA = _____ (Autumnal _______).– __________________________– Where is the Sun straight up?– Why do you think it’s called an equi-nox?

Season start dates & what happensLook at the previous pictures. You should be able to convince yourself that the seasons are _______________________________________. You should also understand why.

See also pages _________.

nightday

NP

SP

nightday

NP

SP

nightday

NP

SP

What is the weather like DURING THE DAYTIME shown in figure __ below?

day

BC

A

D

GF

EH

B C

A

D

GF

EH

BC

A

D

GF

EH

0

0 1. Hot

2. Cold

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80

nightday

NP

SP

Which letter is hottest at noon?B

C

A

D

GF

E

0

0

0

0

0

0

0 1. A

2. B

3. C

4. D

5. E

6. F

7. G1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80

nightday

NP

SP

nightday

NP

SP

nightday

NP

SP

What season is it for the letter shown in figure __ below?

day

BC

A

D

GF

EH

BC

A

D

GF

EH

BC

A

D

GF

EH

000 1. Summer

2. Winter

3. Cannot be determined

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80

nightday

NP

SP

Which date is it?B

C

A

D

GF

EH

0

0

0

0 1. March 21

2. June 21

3. Sep 21

4. Dec 21

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80

Now you’re ready for the test

• But just in case…

• Try the Seasons Ranking Tasks handout for practice (outside of class).

PrecessionSee pages 40-41 in textbook for this topic. (chapter 2)

You’ve probably noticed that the sky has changed a little __________ ______________________ The ancients knew about this, but it did take several hundred years of observations to figure it out.

As we’ve discussed before, the Earth’s rotation axis is tilted ________ away from its revolution axis around the Sun.

The __________________________. _________________________, however, _____. It ________ in a circle ____________________.

Over 2000 yrs this slow wobble causes a slight change in the zodiac constellations. This is why your “sign” is probably 1 earlier.

_______________________________________________. _________________________________!_________________________________!

Constellation 2000 yrs ago Now Days Sun in the sign

CapricornUS Dec 22 - Jan 19 Jan 19 - Feb 16 28

Aquarius Jan 20 - Feb 18 Feb 16 - Mar 12 24

Pisces Feb 19 - Mar 20 Mar 12 - Apr 19 38

Aries Mar 21 - Apr 20 Apr 19 - May 14 25

Taurus Apr 21 - May 21 May 14 - June 21 38

Gemini May 22 - June 23 June 21 - July 21 30

Cancer June 23 - July 22 July 21 - Aug 11 21

Leo July 23 - Aug 23 Aug 10 - Sep 17 37

Virgo Aug 24 - Sep 22 Sep 17 - Oct 31 44

Libra Sep 23 - Oct 23 Oct 31 - Nov 23 23

ScorpiUS Oct 24 - Nov 22 Nov 23 - Nov 30 7

Ophiuchus Not part of zodiac Nov 30 - Dec 18 19

Sagittarius Nov 23 - Dec 21 Dec 18 - Jan 19 32

 Info from Wikipedia's article about the Zodiac, subtopic: Precession of the Equinoxes. This info will be on the course website.

What’s Your Sign? Then & Now

Overarching questions

• What causes it to be hot and cold?• What things could cause temperature

differences?• What causes Earth summer / winter?• How is the Earth’s tilt related to seasons, if

at all?• What info would you need to know to

predict “seasons” on other planets?• What is precession?