Seasons

1
Seasons

• When why is it hot and cold - Section 2.2

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.

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
REMINDER Planet temperature

• Depends on two things
• ___________________________________
• ___________________________________

5
Absorption of visible light

• Which absorbs more sunlight? Air or water/ground?
  How do you know?
• Things that affect amount of light absorbed
• _____________________
• _____________________________
• Look at the map on page 40. Which is better at
  absorbing _______ light - Water or ground?
• (technical note IR color is important too.
  Why?)
• We wont talk about color anymore. Climate models
  need to account for it we dont.
• ___________________________________

6
Distance

• Many people think seasons are caused by the
  distance to the Sun.
• Were good scientists now, so what should we do?
• Lets __________________!
• 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.

7
Movie coming soon to web page
8
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

9
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 _______time difference strengthen or
  weaken the idea that summer is hot because of
  __________________?
• Well focus on daytime from now on. Nighttime
  arguments yield the same results.

10
Daytime length

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

11
Daytime / nighttime seasons

• It appears we have a good explanation. Our
  temperature observations are explained.
• Daytime length also explains why
  ______________________________.
• _________________________________________________.
  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
  __________________________ _______________________
  _______________________________
• Whats the temperature like there?
• Is the daytime length the only important effect
  for hot/cold?
• _____________________________. But
  _____________________ ____________________________
  ___________________________!

12
Season causes whats dominant?

• So, weve ____________________________ as the
  dominant effect!?!?!
• Earth-Sun _________________________ for people in
  US
• Earths ___________________________
  month-to-month
• _________________ doesnt explain
  _________________________ at any time of year,
  but
• _________________________________________________
  __.
• 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?

13
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.

14
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 __________________________________________!
• Is this going to be a big effect or small effect?
  Why?
• Work on Lecture Tutorial, page 93 ONLY

15
Sun is _________________ 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? Which is hotter, C
or the equator? Which hemisphere is hotter north
or south? (Clicker)
Earth
16
Ask your neighbor Which hemisphere is hotter?

1. North
2. South
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
17
Two pictures

• The next slide shows how the Earth looks on 2
  important dates.

18
Looking from one side
NEIGHBOR On this drawing, which hemisphere has
summer? How can you tell?
Copy this drawing into your notes
NEIGHBOR On this drawing, which hemisphere has
summer? How can you tell?
This date is ________
This date is __________
19
Lecture Tutorial

• Work on Pages 94-96.

20
Season start dates what happens
Look at the previous pictures. You should be able
to convince yourself that the seasons are
_______________________________________. You
should also understand why.

• ____ (6/21) ______. In LA _____________. How
  about in Australia?
• ______________________ (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 its called an equi-nox?
• ______________________. In LA _____ (Autumnal
  _______).
• __________________________
• Where is the Sun straight up?
• Why do you think its called an equi-nox?

See also pages _________.
21
Now youre ready for the test

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

22
Precession
See pages 40-41 in textbook for this topic.
(chapter 2) Youve 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 weve discussed
before, the Earths 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. ____________________
___________________________. _____________________
____________!_________________________________!
23
Whats Your Sign? Then Now
24
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?