1. Why is it so hot here in the summer?

2. The Earth in Space
TEK 8.7A – the student knows the effects resulting from cyclical movements of the Sun, Earth, and Moon. The student is expected to model and illustrate how the tilted Earth rotates on its axis, causing day and night, and revolves around the sun causing changes in seasons.

3. Rotation - Earth spinning on its axis
Earth’s rotation on its axis causes day and night
It takes 24 hours for Earth to rotate once on its axis
Earth rotates in a counter- clockwise direction
Earth rotates at about 1,600 kilometers per hour
Rotation Animation
Day and Night Song

4. The movement of one object around another object
Revolution
The movement of one object around another object
Earth travels (revolves) around the sun
One complete revolution around the sun equals a year
It is a curved path (elliptical) followed by Earth as it moves around the Sun
Earth’s orbit is about 365 ¼ days (Leap year every four years)

5. Revolution

6. Now You Try!
Stand in place, and make one complete turn (You have just rotated)
Take a trip around your chair (You have just revolved
Do you think you can rotate and revolve at the same time? Try it now!

7. Think about what a spinning top, a race car on an oval track, and a globe have in common

8. Turn to your neighbor and explain…
What is the difference between Earth’s rotation and Earth’s revolution?

9. Earth in Space Earth revolves rotates On its axis Around the sun
causing
Years
Day and night

10. So now you understand day and night – What about seasons?
A Year in 40 seconds

11. Tilt A Whirl!
Earth has seasons because its axis is tilted as it revolves around the sun
If Earth’s axis were straight up and down, temperatures would remain constant year round (no seasons)

12. Seasons Seasons are caused by the tilt in Earth’s axis
The tilt causes uneven heating by the sun (seasons)

13. Why is it warmer near the equator than near the poles?
At the equator - sunlight hits Earth’s surface more directly
Near the north and south poles - sunlight hits Earth’s surface at an angle (energy from the sun is spread out over a greater area)

14. The Earth's axis is tilted by 23.5°
The Earth’s Tilt
The Earth's axis is tilted by 23.5°

15. Earth’s axis always points in same direction (towards Polaris - the North Star)

16. Earth’s Tilted Axis
Earth’s axis is tilted away from the sun for part of the year and toward the sun for part of the year
When tilted toward the sun – summer
When tilted away from the sun - winter
Note: Summer and winter are not affected by changes in Earth’s distance from the sun.

18. Summer in the Northern Hemisphere
Axis is pointing towards the sun

19. Winter in the Northern Hemisphere

20. As the Earth moves around the Sun, this axis always stays pointing in the same direction.

21. Look at the direction of the axis during each season.

22. Direct vs. Indirect Light

23. When the northern hemisphere is leaning away from the sun, the rays coming from it hits this part of the Earth at a smaller (slanted) angle compared to other parts of the world
These are called indirect rays
Indirect rays - same amount of energy spread over a larger area of the earth therefore it receives less energy (heat)

24. Winter Sun (Indirect) Summer Sun (Direct)
Teacher demos with a flashlight
Winter Sun (Indirect)
Summer Sun (Direct)

25. Winter Sun (Indirect) Summer Sun (Direct)
Teacher demos with flashlight and globe

26. Seasons Direct sunlight gets more heating
Indirect sunlight gets less heating

27. Misconception Alert!
Seasons are NOT caused by the changing distance the Earth is from the Sun.
The Earth travels in an elliptical orbit, so the distance does vary – but not enough to cause the change in temperature associated with seasons!

28. When the southern hemisphere is experiencing summer, the northern hemisphere has winter (what do you know about Australia?)

29. 6 months later, the situation reverses, and it is now winter in the southern hemisphere since that part of the earth is now leaning away from the sun

30. The energy that hits the Earth by the Sun changes over of the year
The angle the Sun is above the horizon determines how much heat and light strike each square meter of ground

31. This means that in summer, the ground receives more energy (more heat) per square meter than in the winter. 
More energy is received by the ground during the summer (high temperatures) and less energy during the winter (lower temperatures).

32. Sun’s Angle Analogy
If you had $ to divide among 50 people what would each person get?
If you had the same $ to divide among 100 people what would each person get?
If you had the same $ to divide among 200 people, what would each person get?

33. Sun’s Angle = money Think of the money as the sun’s power
The sun always shines with the same amount of power, just like the $
If you had to spread the power over a larger area, there would be less power (heating) to go around on that area on Earth.
Just like there is less money for each person if the number of people grows.

34. Changes in the Sun’s Angle
Summer
Sun is more directly overhead
Sun’s energy is concentrated
Winter
The sun is less directly overhead
Sun’s energy is less concentrated

35. Seasons and Earth’s Tilt

36. Seasons
Question…
The amount of energy is always the same, so why do we have seasons?
First reason: the earth is tilted, what’s the second reason?

37. Big Idea:
The seasons are the result of: 1) the tilt of the Earth's axis, and 2) revolution around the sun
If the tilt of the Earth's axis was 0° there would be no difference in how the rays from the sun hit its different regions (there would be no seasons)

38. Review Look closely at where the Sun is hitting the Earth during each season:
Point out summer solstice and winter solstice

39. Solstice
Solstice: Either of the two times in the year, the summer solstice and the winter solstice, when the sun reaches its highest or lowest point in the sky at noon, marked by the longest and shortest days.

40. Make a quick T chart in your notes
Winter Solstice Summer Solstice

41. Winter Solstice
The northern hemisphere is pointed furthest away from the sun
The sun is directly over the Tropic of Capricorn
The shortest day of the year in the northern hemisphere

42. Summer Solstice
The northern hemisphere is pointed furthest toward the sun
The sun is directly over the Tropic of Cancer
The longest day of the year in the northern hemisphere

43. Solstices
On two days each year, the noon sun is overhead at either ° S or 23.5° N – solstices.
Winter Solstice
23.5° S
in the northern hemisphere
December 21st
shortest day of the year
Summer Solstice
23.5° N
June 21st
Longest day of the year

44. Equinox
Equinox: the date (twice each year) at which the sun crosses the equator, therefore day and night are of equal length (about September 22 and March 20).

45. Make a quick T chart in your notes
Spring Equinox Fall Equinox

46. Spring and Fall Equinox
Vernal (spring) and autumnal (fall) equinox - the sun is directly over the equator
Days and nights are equal in length

47. Earth in March and September
Equinox (means - Equal night)
Halfway between the solstices, neither hemisphere is tilted toward or away from the sun
The noon sun is directly overhead at the equator

48. Vernal (Spring) Equinox
March 21st
Marks the beginning of spring in the northern hemisphere

49. Autumnal Equinox September 23rd
Marks the beginning of fall in the northern hemisphere

50. Equinoxes and Solstices

51. Videos
Seasons Animation