1. Reason for Seasons

2. Do now: Why do you think we have different temperatures during the different seasons?

3. Most people think it’s the distance between us and the sun
Most people think it’s the distance between us and the sun? Are you one of them? Let’s see if you are right!

4. What are the two motions Earth makes in space?
Rotation - spinning
Revolution – going around the sun.

5. Tilt
An axis is an imaginary line that runs through the center of the Earth and is what we rotate around.
We are tilted 23.5 degrees from being straight up and down. This means we have a tilt of 23.5 degrees.

6. What do Tim and Moby have to say about the seasons?
The Four Seasons

7. 1. Tilt of Earth’s Axis
During the summer, we (in the northern hemisphere) are tilted towards the Sun

8. This means we will have warmer temperatures in the northern hemisphere
This means we will have warmer temperatures in the northern hemisphere It’s summer!
The northern hemisphere is leaning towards the sun making it summer.

9. Why does leaning affect temperature?
It has to do with direct and indirect insolation (rays of sun).
When the sun is straight overhead it makes the rays more concentrated and therefore hotter. The more spread out the rays the less concentrated and so the colder the temperatures.

10. More concentrated – 90 degree angle of insolation.
Less concentrated – lower angle of insolation.

11. In places the sun shines on directly (with a 90 degree angle) the temperatures will be hotter – where it is not direct or indirect (a lower angle) it will be colder.

13. 2. Revolution
The earth does not stay in one place but the tilt always stays the same. This is called parallelism. This means that different places on Earth will receive direct or indirect rays of insolation depending on the time of year.

14. On Dec. 21, 231/20S receives the direct ray.
On June 21st – 231/20N receives the direct ray.
On Sept. 22 and March 20 the equator receives the direct rays since neither the northern or the southern hemispheres are leaning towards the sun.

15. Earth Revolution Animation

16. A closer look at the 1st day of each of the seasons.

17. Summer Solstice June 21st – longest day of the year!
Earth’s axis is tilted towards the Sun
Sun has the longest path in the sky

18. 15 hours of daylight and 9 hours of darkness
Sun rises in the NE and sets NW
Sun’s direct rays hit the Tropic of Cancer (23 ½ oN)

19. The Sun’s direct rays hit the Tropic of Cancer on June 21st.

20. Summer Solstice
Notice how the number of hours of daylight increases as you go higher in latitude. The Artic Circle is experiencing 24 hours of daylight.

21. How many hours of daylight is the Antartic Circle experiencing on the summer solstice?
0 hours – it experiences 24 hours of darkness.

22. Winter Solstice December 21st – shortest day of the year
Earth’s axis is tilted away from the Sun
Sun has the shortest path in the sky

23. 9 hours of daylight and 15 hours of darkness
Sun rises in the SE and sets in the SW
Sun’s direct rays hit the Tropic of Capricorn (23 1/2o S)

25. Equinoxes March 21st and Sept. 23rd
12 hours of daylight and 12 hours of darkness (equal)

26. Sun rises exactly East and sets exactly West
Sun’s direct rays hit the Equator

27. Equinoxes

29. Diagram summarizing seasons

30. Summary of the cause of seasons:
The Earth’s axis is tilted causing parts of the Earth to be tilted towards or away from the sun.
The Earth’s axis does not change – parallelism (the axis remains parallel to its previous position as Earth revolves around the Sun).
Earth revolves around the sun changing its position.
So does the distance between the Earth and the Sun cause the seasons?
NO! We are actually closer to the sun in the winter!!

31. Daily path of the sun.
When we diagram the path of the sun on the first day of each of the seasons it would look like this. What do you notice about the summer’s path? Winter path?
Summer path is long. Winter path is short.

32. The Noon Sun
At noon, the Sun has reached its highest point in the sky for that day
In N.Y. (lat. ~42o), the Sun will NEVER be directly overhead at your zenith
Noon

33. The highest angle (73. 5o) the Sun ever reaches in N. Y
The highest angle (73.5o) the Sun ever reaches in N.Y. is on the Summer Solstice
Only at latitudes between 23 ½ o N & 23 ½ o S can the noon Sun be directly overhead

34. Where does the Sun rise and set on the Summer Solstice?
Rises NE
Sets NW

35. Where does the Sun rise and set on the Equinoxes?
Rises E
Sets W

36. Where does the Sun rise and set on the Winter Solstice?
Rises SE
Sets SW

37. Which season does the Sun have the longest path in the sky?
Summer

38. At noon in the northern hemisphere, towards which direction would an observer look to find the Sun?
SOUTH

39. 73.5o
50o
26.5o
New York
Notice the angle of the sun changes 23 ½ degrees higher or lower as you go from one season to the next.

40. Must know season facts!! If you know this chart you have the basics!
Day Begins
Place receiving 900 angle
Sunrise/sunset
Length of day and night
Summer
Solstice
Fall
equinox
Winter
Spring
Northeast/
Northwest
15 day
9 night
June 21
Tropic of Cancer
Sept 21
East
West
12 day
12 night
Equator
Southeast
Southwest
9 day
15 night
Tropic of Capricorn
Dec 21
March 21
Equator
East
West
12 day
12 night

41. Watching the daily path of the sun.