1. Earth’s Seasons

2. What do we know about Earth?
Sphere
Rotates on axis
Has a magnetic field
Orbits the sun

3. Earth has seasons
Season: A time of year marked by a change in weather, ecology, and amount of daylight

4. What do seasons look like around Earth?
Summer
NJ-warm, more daylight, June-August
Hawaii-80’s, 12 hours of daylight
Alaska- up to 24 hours of light
Australia-Dec-Feb
Winter
NJ-cold, less daylight, Dec-Feb
Hawaii- 80’s, 12 hrs of daylight
Alaska- up to 24 hours of darkness
Australia-June-Sept.

5. Does distance from the sun cause the changes in temperature and daylight?

6. Distance from the sun does NOT cause our seasons.
If it did, we would all feel winter in July and summer in January.
Even Hawaii would have a cold winter!

7. So what causes the seasons?

8. The tilted axis of the Earth causes seasons
The axis is tilted 23.5˚

9. The tilt was likely caused by the impact of the planetessimal that collided with Earth 4.4 billion years, forming the moon.

10. The Earth is always tilted the same direction during its yearly revolution around the sun.

11. Earth’s tilt and its orbit affect how much sunlight each area on Earth receives

12. Which sunlight angle will be produce higher temperatures?

13. Types of Light from the Sun
Direct Light
Indirect Light
Which one will result in higher temperatures?

14. Direct Light
Areas receiving direct light from the Sun have a greater concentration of sunlight, therefore higher temperatures.

15. Summer with warmer temperatures is caused by the direct light –a result of the sun being higher in the sky

16. Indirect Light
Areas receiving indirect light from the sun have the sunlight spread over a larger area, therefore cannot heat as well.
Cooler temperatures result

17. Winter has indirect light due to the sun being lower in the sky
Winter has indirect light due to the sun being lower in the sky. Cooler temperatures result.

18. The sun’s path across the sky is higher in the summer and lower in the winter

19. Combine the sunlight angle with the amount of hours of sunlight.
Long daylight hours & direct light = summer
Short daylight hours & indirect light = winter

20. Sunlight strikes the hemisphere tilted towards the sun more directly than the hemisphere tilted away.
Summer occurs in the hemisphere tilted towards the sun. (direct light)
Sun

21. Sun What season is it? Northern Hemisphere-Winter
Southern Hemisphere-Summer
Sun

22. Seasons Interactives

23. So what causes the seasons?
The Earth’s tilt causes the seasons!
Are you smarter than a Harvard Grad?

24. Special Times of the Year

25. Solstice
The day when the direct sunlight reaches its greatest distance north or south of the equator.

26. Summer solstice in Northern Hemisphere: June 21 or 22 (longest daylight of the year)

27. Winter solstice in Northern Hemisphere: December 21 or 22 (shortest daylight of the year)

28. Equinox
When the sun is directly above the Earth’s equator. Daylight hours are nearly equal all over Earth.
Neither the N. or S. Hemisphere is tilted towards the sun.

29. Northern Hemisphere Equinoxes:
Spring equinox-March 20 or 21
Fall equinox-September 22 or 23

30. Seasons are opposite for the Southern Hemisphere

31. Review Quiz

32. Which diagram correctly shows Earth’s orbit around the sun?

33. Identify for the N. Hemisphere: Summer solstice Winter solstice
Fall equinox
Spring equinox D
Spring C A
Winter
Summer B
Fall

34. How do we know the Earth is a sphere?
-satellite photos
-curved shadow on moon during a lunar eclipse.
-approaching ships “rise” over the horizon

35. What is an axis?
The imaginary vertical line around which the Earth spins.

36. What does “A” represent? What does “B” represent?
A-Revolution B-Rotation B A

37. How long does one complete rotation take on Earth?
24 hours

38. How long does one complete revolution of Earth take?
365 days (1 year)

39. Why is a magnetic field important?
It protects Earth from CME’s from the Sun

40. How do we have a magnetic field?
The motion of the liquid metal inside Earth and our daily rotation cause it.

41. What causes the seasons?
TILT! TILT! TILT!

42. What season is it in the Southern Hemisphere?
Summer-southern hemisphere is tilted towards the sun = direct light = summer!
Sun

43. What type of light makes hotter temperatures?
Direct!

44. Where is the sun during the equinox?
Directly over the equator.

45. What’s the difference between northern and southern hemispheres’ seasons?
They are opposite!
Easter is celebrated in the fall (March or April)
Christmas (December) in Australia is warm!

46. Review of Seasons