Seasons
What do your students think causes the seasons?
Images at http://nix.ksc.nasa.gov/info
Created by the Lunar and Planetary Institute
For Educational Use Only
LPI is not responsible for the ways in which this powerpoint may be used or altered.
Let’s start with a couple “probes”
Snowball!
Let’s Look at Some Data!
• Temperatures around the World
Average Daily Temperatures (°F) in Tourist Cities
(from http://www.infoplease.com/ipa/A0004587.html ))
January
April
July
October
Cape Town (South Africa)
69
66
60
65
Caracas (Venezuela)
75
81
78
79
London (United Kingdom)
44
56
73
58
Mexico City (Mexico)
66
77
73
70
Montreal (Canada)
22
51
79
56
Moscow (Russia)
21
47
76
46
Nairobi (Kenya)
77
75
69
77
Paris (France)
42
60
76
59
San José (Costa Rica)
75
79
77
77
Seoul (Korea)
33
62
84
67
Singapore
86
89
87
88
Stockholm (Sweden)
31
45
70
48
Sydney (Australia)
79
73
62
72
Tokyo (Japan)
48
64
84
70
Let’s Start with some Observations
• Using free downloaded computer program,
Stellarium: http://www.stellarium.org/
– Stellarium is planetarium software that shows exactly what
you see when you look up at the stars. It's easy to use, and
free.
• Let’s look at sunrise & sunset, and Sun’s height in the
sky.
December
True color images
March
June
September
Images at http://www.nasa.gov/vision/earth/features/blue_marble.html
Animation-Earth’s Life through Seasons
Modeling the Seasons
Time to grab a styrofoam ball and a light!
Height of Sun for USA
Winter: The Sun rises in the southeast, stays
low in the sky, and sets in the southwest.
Spring: The Sun rises due east, moves higher
in the sky than in winter, and sets due west.
Summer: The Sun rises in the northeast,
travels high (near zenith), and sets in the
northwest.
Fall: The Sun rises due east, travels to a
medium-height in the sky, and sets due west.
What Causes Earth’s Seasons?
• Earth’s axis is tilted 23.5 degrees – it always points in
the same direction (Polaris, the North Star) as we
orbit our Sun once a year
• This tilt causes the hemispheres to alternate in the
amount of our Sun’s light and heat they receive
through the year
Image at http://www.lpi.usra.edu/education/skytellers/seasons/about.shtml
Northern Hemisphere Summer
More daylight hours, more direct sunlight
Image at http://www.lpi.usra.edu/education/skytellers/seasons/about.shtml
Earth’s orbit is almost a perfect circle
• Earth is CLOSEST to our Sun (91 million
miles) in winter—January 3
• Earth is farthest from on our Sun (94
million miles) in summer –July 4
Daylight Hours Across the Globe
Time is indicated as number of hours (h)
Miami
Brisbane
Nairobi
Punta Arenas
Jan
Feb
10.5 h 11 h
Mar
12 h
Apr
12.5 h
May
13 h
Jun
14 h
Jul
Aug
14.5 h
14 h
Sep
12.5 h
Oct
12.5 h
Nov
11 h
Dec
11.5 h
14.5 h
13.5 h 13.5 h 12.5 h
11 h
11 h
11 h
11.5 h
11.5 h
12.5 h
14 h
14.5 h
12 h
12 h
12 h
12 h
12 h
12 h
12 h
12 h
12 h
12 h
8.5 h
8.5 h
9.5 h
11.5 h
13 h
15 h
16.5 h
12 h
12 h
17.5 h 15.5 h
13.5 h 11.5 h
10 h
Nome
5h
7h
10 h
13.5 h
17.5 h 21.5 h
22 h
18 h
15.5 h
11.5 h
8.5 h
5.5 h
Singapore
12 h
12 h
12 h
12 h
13 h
12 h
12 h
12 h
12 h
12 h
12 h
Cape Town
15 h
14 h
13.5 h 12.5 h
11.5 h 10 h
10.5 h
11 h
11.5 h
12.5 h
14 h
14 h
Seattle
9h
10 h
11 h
13.5 h
15 h
17 h
16.5 h
15.5 h
13.5 h
11.5 h
10.5 h
9.5 h
Vostok
24 h
24 h
19 h
14.5 h
0h
0h
0h
0h
7h
15 h
24 h
24 h
13 h
http://www.lpi.usra.edu/education/skytellers/seasons/activities/light.shtml
Seasons on Other Planets
• In some cases, the changing distances from the Sun
will affect the seasons.
• In others, the axial tilt will make a huge difference!
Image at http://photojournal.jpl.nasa.gov/catalog/PIA02963
Image at http://photojournal.jpl.nasa.gov/catalog/PIA01589
Seasons on Planets
Planet
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Axial Tilt
0°
177°
23°
25°
3°
27°
98°
30°
Eccent.
0.21
0.01
0.02
0.09
0.05
0.06
0.05
0.01
Orbit
88 days
224 days
365 days
686 days
12 years
30 years
84 years
165 years
Perihelion
28 mill. Miles
Aphelion
43 mill. miles
91 mill. miles 94 mill. miles
129 mill. miles 155 mill. miles
Mars’ Orbit and Seasons
At vernal equinox, Mars is 145
million miles from the Sun
At winter solstice, Mars is 128
million miles from the Sun
At summer solstice, Mars is 153
million miles from the Sun
At autumnal equinox, Mars is 134
million miles from the Sun
Original images from http://photojournal.jpl.nasa.gov/index.html
An Assessment
• Best procedures: read quietly to yourself
(so you don’t give any subconscious clues)
• As the instructor, we read it too, for timing, then ask if anyone
needs more time
• If not, it’s time to vote simultaneously—use your fingers, right
in front of your chest so others don’t see (anonymous)
Northerners have cold days in January because
1. the Earth is farthest from the Sun in January.
2. the sunlight takes a longer route to get to the
Earth in January.
3. the Sun is lower in the sky in January.
4. El Nino is always strongest in January.
Another
Which of the following statements help explain why
summer days tend to be hotter than winter days?
In that region,
a)
b)
c)
d)
1.
2.
3.
4.
5.
The day is longer.
The Earth’s surface receives more light per unit area.
The light is coming more directly from the Sun.
There is no snow to cool the Earth.
Just a
Just c
a and d
a and c
b and c
What would the days and seasons be like in Houston if
the Earth still rotated at the same speed, but the Earth’s
axis were tilted nearly 50 degrees on its side instead of 23
degrees?
1. Both days and seasons would be half a year long.
2. The days would be the same length, but the
seasons would be half a year long.
3. There would be no seasons, but days would be 6
months long.
4. The days and seasons would be the same lengths
as ours, but the seasons would have more extreme
temperature changes.