Seasons
When & why is it hot and cold - Section 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/terminology.
• 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.
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?
REMINDER: Planet temperature
Depends on two things:
1. ___________________________________
2. ___________________________________
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?
–
(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. ___________________________________
Distance
Many 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 _______time difference strengthen
or weaken the idea that summer is hot
because of __________________?
• We’ll focus on daytime from now on. Nighttime
arguments yield the same results.
Daytime length
• Our next question:
– Why are daytime and nighttime lengths
different at different places?
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 __________________________
______________________________________________________
• 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 US
2. Earth’s ___________________________ month-to-month
3. _________________ 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?
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.
Sun location & temperature
Why 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
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?
A
B
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
Ask your neighbor: Which
hemisphere is hotter?
Earth
1. North
2. South
3. Cannot be determined
0
23°
23°
0
0
day
night
23°
23°
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Two pictures
• The next slide shows how the Earth looks
on 2 important dates.
Looking from one side
NEIGHBOR: On this drawing, which hemisphere
has summer? How can you tell?
Copy this drawing into
your notes
Sun
NEIGHBOR: On this drawing, which
hemisphere has summer? How can you tell?
This date is ________
This date is
__________
Lecture Tutorial
• Work on Pages 94-96.
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.
•
•
•
•
___________________. In LA = _____. (Vernal ________)
See also pages
– _________________________ (in north)
_________.
– Where is the Sun straight up?
– Why do you think it’s called an equi-nox?
____ (6/21)= ______. In LA = _____________. How about in Australia?
– ______________________ (in north)
– Where is the Sun straight up?
– What happens inside the Arctic circle? Antarctic circle?
______________________. In LA = _____ (Autumnal _______).
– __________________________
– Where is the Sun straight up?
– Why do you think it’s called an equi-nox?
Dec 21 = __________. In LA = ____________. How about in Australia?
– ________________________ (in north)
– Where is the Sun straight up?
– What happens inside the Arctic circle? Antarctic circle?
Now you’re ready for the test
• But just in case…
• Try the Seasons Ranking Tasks handout
for practice (outside of class).
Precession
See 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.
_______________________________________________.
_________________________________!
_________________________________!
What’s Your Sign? Then & Now
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.
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?