1. The Reasons for the Seasons

2. Rotation
Earth spins on its axis (An imaginary line through center of Earth from the North to South Pole)
Earth’s rotation is counter clockwise as seen from North Pole
Earth spins on its axis like a top

3. Rotation - Axis Earth is tilted on its axis at an angle of 23.5°
Polaris
Rotation - Axis
Earth is tilted on its axis at an angle of 23.5°
Earth’s axis is currently pointed at Polaris (the North Star)
NOTE: As the Earth orbits The Sun, the axis is always pointed at Polaris. This is why we have seasons.
NOTE: Although our axis is currently pointed at Polaris, the axis “wobbles” (moves back and forth) and will eventually point to another star in the night sky (This is called “precession”.)

4. Rotation Earth rotates on its axis once every 24 hrs
Earth’s rotation causes day & night
Earth’s rotation causes celestial objects to appear to move from east to west in Northern Hemisphere
The background image was taken from the space station astronauts showing the day/night terminus as Europe and Africa are passing from Day to Night.
The Sun is on the left; therefore, the lighted side of the Earth is on the left.

5. Interactive Day-night Map
Night and Day Map
This is actually a map that tracks day and night across the globe. The * at about 50°W represents the location of The Sun’s most direct rays hitting the Earth. The darkest areas are night, the lightest area is day. The grayer areas is the twilight.
Note: There are many versions of this map that can be bought to hang on your wall. As will be pointed out later in this PPT, you can also use this to determine the approximate season. In this case, it is either late spring or late summer due to the Sun’s proximity to the equator.
The INTERACTIVE DAY-NIGHT MAP is the same as the image on this slide, but you can change the time, speed up or slow down (even go back in time), change the month, etc. Use it to have students predict seasons and time by examining the Sun’s position and when the N or S pole is in 24hr light/dark.
Interactive Day-night Map

6. Just Checking… THINK…PAIR…SHARE
What does it mean when we say the Earth rotates?
How would you define or explain the concept of Earth’s axis?
Have students answer these in a think, pair share format.
Answer:
Earth spins on its axis once every 24 hrs causing night and day.
The imaginary line passing through the Earth from North Pole to South Pole that always points to the north star, Polaris, upon which the Earth spins.

7. Revolution The movement of one object around another
Earth revolves around our Sun counterclockwise
Earth’s orbit is almost circular rather than oval shaped but is still referred to as an elliptical orbit
365 ¼ days to revolve once around the Sun (~ a year)
It is a GREAT time to discuss, “What is wrong with this model?”
Note that the orbit path is “very” elliptical. This is an optical illusion. It happens because you are not looking straight down on the Earth and Sun. Since you are looking at it more from the edge, it makes the orbit appear more elongated.
* You can show this illusion to students using an embroidery hoop or other small (about 6-8” in diameter) circular object and your data projector. Hold the loop in the light project so that it makes a shadow on the screen that is as close to circular as possible. Slowly tilt the top edge towards the screen and ask the student to tell you what is happening (although the hoop is circular, the shadow will change to elliptical.)

8. Are you there yet?
The imaginary line that runs through the north and south poles of the Earth is called the
Equator
Axis
Longitude
Latitude
ANSWER: B, Axis

9. What’s the diff. Decide weather each example is of A. Rotation or B
What’s the diff???? Decide weather each example is of A. Rotation or B. Revolution
A. Rotation
The Earth spinning on it’s axis.
A baseball player running around the infield.
Takes 1 year
A top spinning
Causes day and night.
Takes 24 hours
The moon circling the Earth
B. Revolution
B. Revolution
A. Rotation
Note, as you click, the question will pop up and the next click will bring up the answer. The next click will remove the answer and bring up the next question.
A. Rotation
A. Rotation
B. Revolution

10. Two Primary Reasons for the Seasons (on Earth)
The Earth is tilted
on its axis at 23.5°
2. The angle sunlight
hits the Earth as it revolves
around the sun.

11. Location and Distance in Orbit
NOTE: This would be a very good time to show students why the models appear more elliptical than they really are by using something that is circular (See 5E notes about embroidery hoop)
Seasons occur due to the tilt of the Earth’s axis & revolution around the Sun.

12. Seasons Northern hemisphere tilts towards Sun = summer (warmer)
Which numbered Earth represents Summer
in the Northern Hemisphere?

13. Seasons Northern hemisphere tilts away from Sun = winter (cooler)
Which numbered Earth represents Summer
in the Northern Hemisphere?
Which numbered Earth represents Winter
in the Northern Hemisphere?

14. Seasons Which numbered Earth represents Fall
in the Northern Hemisphere?
Which numbered Earth represents Summer
in the Northern Hemisphere?

15. Seasons Which numbered Earth represents Spring
in the Northern Hemisphere?
Which numbered Earth represents Summer
in the Northern Hemisphere?

16. Seasons
In the Spring and the Fall, the tilt of the Earth is such that the spread of sunlight shines on the Earth approximately equally
Remind students of the activity with the box and how much light was shining in a certain amount of area
Ask the students:
Why then if the amount of light (not spread out over a larger area or more condensed in one area) is approximately equal, why are the fall and spring months not the exact same temperatures (spring is usually moving from cooler to warmer temperatures and the fall is moving from warmer to cooler temperatures)?

17. Seasons
Southern hemisphere seasons are opposite Northern hemisphere seasons
If its Winter here, then Australia is having _?_.
Summer….that’s right, Australians go swimming during Christmas and snow skiing on the 4th of July…Yes, Australia HAS a 4th of July, they just don’t celebrate it.
Please note “ELLIPTICAL ILLUSION” of Earth’s orbit again.

18. Solstices
Occur twice yearly when the Sun is directly over “Tropics” (23.5°N and 23.5°S Latitude)
Summer Solstice is the longest day of the year in the Northern Hemisphere (Sun directly over Tropic of Cancer-23.5°N-at noon)
Winter solstice = shortest day of the year for Northern Hemisphere (Sun directly over Tropic of Capricorn-23.5°S-at noon)
This is for the U.S. and the Northern Hemisphere.
* Ask students: Do you notice anything about the location of the noon Sun in relation to the tilt of Earth’s axis?
The tilt of the axis and the location of the tropics are the same degree. Does not change.
Please note “ELLIPTICAL ILLUSION” of Earth’s orbit again.

19. Equinox Means equal amounts of night & day They occur twice each year
They occur half-way between solstices
Neither hemisphere tilts towards or away from the Sun
At noon, the Sun is directly over equator
Carrollton is ~33°N of the equator. Therefore, we will NEVER see the Sun DIRECTLY overhead.
Be sure to emphasize that it is the sun’s energy that strikes perpendicular to the Earth’s surface where the most energy is absorbed. Note that the top and bottom “Sun rays” are hitting the Earth at an angle to the surface. This causes some of the energy to “bounce” off the atmosphere back into space rather than being absorbed at the surface.

20. Turn and Talk about the Equinox
The Sun will be at its highest point in our sky at noon but never directly overhead in Carrollton, Texas… why do you think this is true?
Carrollton is ~33°N of the equator. Therefore, we will NEVER see the Sun DIRECTLY overhead. (Summer solstice…Sun directly over 23.5°N…its highest point in the northern hemisphere.)

21. Where are we? Your answer should refer to Carrollton TX.
This occurs because the Earth’s axis is tilted as it moves around the Sun.
This occurs when the Northern hemisphere is tilted towards the Sun.
This is when the length of day and night are equal.
The shortest and longest days of the year when the noon Sun is directly overhead at 23.5 degrees.
This occurs when the Northern hemisphere is tilted away from the Sun.
Winter
Summer
Solstice
Equinox
All of the above

22. Based on this Night and Day Map…
What season do you think it is in Carrollton?
What time do you think it is in Carrollton?
Allow students to answer and explain their reasoning….allow for debate until class settles on an answer.
It must be summer because the north pole region is under 24 hours of daylight.
Since its summer, we would be on daylight savings time. Since the Sun sets between 8:30 & 9 during the summer and its just setting on the tip of Florida, then it should be hours earlier for us (Eastern time in Florida, central time here). Therefore, it is between 7 & 8 PM here (~ 7:30 PM)