1. L.O: SWBAT explain why the tilt of Earth’s axis gives Earth its seasons.

2. They are the first day of the seasons
Why is March 21st “important”?
Why is June 21st important?
Why is September 22nd important?
Why is December 21st important?

3. There are three major reasons for the changing seasons on Earth.
Earth’s Tilt
The Earth’s revolution
Earth’s constant tilt

4. We would NOT have seasons if earth’s axis was perpendicular
Earth’s Tilt
Due to Earth’s tilt of 23.5 degrees each position on earth is receiving a different angle of insolation.
We would NOT have seasons if earth’s axis was perpendicular

5. if earth didn’t revolve around the sun. we’d have no seasons.
2. The Earth’s revolution around the sun causes different hemispheres to receive different angles of insolation during different months.
if earth didn’t revolve around the sun. we’d have no seasons.

6. 3. Earth’s constant tilt throughout the year is referred to as parallelism.
This causes the Northern and Southern Hemispheres to receive different amounts of sunlight over the course of the year.
The longer the duration of insolation the more exposure you have to the sun through the day, therefore the warmer you will be.

7. the southern hemisphere’s seasons are the reverse of the North’s seasons.

8. When you get a diagram like this you should always determine which way the northern hemisphere is tilted.

9. At one of the positions the North Pole will be tilted toward the sun.
At one of the positions the North Pole will be tilted away from the sun.
At two of the locations the North Pole will neither be tilted towards nor away but into outer space.

10. Which numbered & lettered position is the North Pole tilted towards the sun? ______
Which numbered & lettered position is the North Pole tilted away from the sun?_____
Which two numbered positions & lettered are the Poles tilted neither towards nor away from the sun? __________

11. Earth is located at Position 1 & Letter D on December 21st
The North Pole tilts away from the Sun.
This is the first day of winter in the northern hemisphere and the first day of summer in the southern hemisphere. (NY gets 9 hours of daylight)

12. The Tropic of Capricorn, which has a latitude of 23
The Tropic of Capricorn, which has a latitude of 23.5 degrees SOUTH, is receiving direct rays. Therefore, an observer will have their noontime sun at an altitude of 90 degrees (their zenith).

13. The entire Southern Hemisphere gets the more direct rays and higher angles of insolation. This is what causes it to be warmer.
The Northern Hemisphere receives less direct rays and lower angles of insolation. This is what causes it to be cooler.

14. Draw a side view of the earth on December 21st.

15. Which hemisphere is experiencing the most daylight hours? ___________
Which latitudes experience 24 hours of daylight? ____________
Which latitudes experience 24 hours of darkness? ____________
The hours of daylight decreases as you travel north.

16. Earth is located at Position 3 & Letter B on June 21st
The North Pole tilts towards the Sun.
First day of summer for the northern hemisphere and the first day of winter for the southern hemisphere
This is the longest day of the year for the northern hemisphere! New York receives approximately 15 hours of daylight

17. The Tropic of Cancer, which has a latitude of 23
The Tropic of Cancer, which has a latitude of 23.5 degrees NORTH, is receiving direct rays. An observer will have their noontime sun at an altitude of 90 degrees (their zenith).

18. The entire Northern Hemisphere gets the more direct rays and higher angles of insolation. This is what causes the temperatures to be warmer.
The Southern Hemisphere receives less direct rays and lower angles of insolation. This is what causes the temperatures to be cooler.

19. Draw a side view of the earth on June 21st.

20. Which hemisphere is experiencing the most daylight hours?
Which latitudes experience 24 hours of daylight? ____________
Which latitudes experience 24 hours of darkness? __________
The hours of daylight increases as you travel north.

21. Earth is located at position 2 & Letter A on March 21st (Spring or Vernal Equinox). Earth is located on position 4 and Letter C on September 23rd (Fall or Autumnal Equinox). Notice, at this position, the North Pole is pointing into outer space so neither the north or south poles tilt towards the Sun.

22. If it isn’t tilted towards or away from the sun…
If it isn’t tilted towards or away from the sun….. Which latitude specifically gets the Sun’s direct rays? _______

23. Equinox – (Equi =EQUAL); ALL points on Earth have 12 hours of daylight and 12 hours of darkness

24. Important !!!
Since the equator is half way between the poles it will be receiving 12 hours of daylight for every day of every year.

25. Draw a side view of the earth on either equinox.

26. Where is the observer at Location A if it is June 21st? ___________ 
Where is the observer at Location A if it is December 21st? ___________
Where is the observer at Location A if it is March21st or September 23rd? ________
How would our seasons be affected if Earth’s axis was not tilted? 
How would our seasons be affected if Earth’s axis was tilted only 10o?

27. The Earth is (5 million km) closer to the sun during the winter months, but it is cold because it leans away from the Sun.

28. What day is “B” and how do you know?
“B” is JUNE 21st (the longest day in the northern hemisphere) because the north is leaning towards the sun.

29. What day is “D” and how do you know?
“D” is DECEMBER 21st (the shortest day in the northern hemisphere. I know because the north is leaning away the sun.

30. What day is “C” and “A” ?how do you know?
SEPTEMBER 23RD
MARCH 21ST

31. WHAT DAY IS THIS AND HOW DO YOU KNOW?

32. WHAT DAY IS THIS AND HOW DO YOU KNOW?