2. Why Do We Have Seasons?

3. We’re here to answer that question.
Some believe we have seasons because we are farthest from the Sun in winter and closest to the Sun in summer.

4. That’s Wrong!

5. If distance from the Sun isn’t responsible, what is?
The Earth’s axis is titled 23.5°.

6. It’s the tilt, baby!

7. The Earth revolves around the Sun.
When you combine the Earth’s tilt and its revolution around the Sun, you get seasons!

8. In the Northern Hemisphere summer, the Earth tilts towards the Sun.
As the Earth revolves around the Sun, different parts of the Earth tilt towards and away from the Sun.
In the Northern Hemisphere summer, the Earth tilts towards the Sun.

9. In the Northern Hemisphere winter, the Earth tilts away from the Sun.
As the Earth revolves around the Sun, different parts of the Earth tilt towards and away from the Sun.
In the Northern Hemisphere winter, the Earth tilts away from the Sun.

10. As the Earth revolves around the Sun, different parts of the Earth tilt towards and away from the Sun.
In the Northern Hemisphere fall/spring, the Earth tilts neither towards or away. from the Sun.

12. The tilt affects the Earth in two important ways.
First, the Earth receives either direct or indirect sunlight (heat energy).
Direct sunlight (heat energy) is received in the Summer.
Indirect sunlight (heat energy) is received in the Winter.

13. The sunlight (heat energy) covers a small area.
We receive direct sunlight (heat energy) when the Sun is high in the sky.
The sunlight (heat energy) covers a small area.

14. The sunlight (heat energy) covers a large area.
We receive indirect sunlight (heat energy) when the Sun is low in the sky.
The sunlight (heat energy) covers a large area.

15. Look at this diagram. It shows direct and indirect sunlight (heat energy) side-by-side.

16. During summer, it covers a smaller area and is warmer.
We always get the same amount of sunlight/heat energy throughout the year.
During summer, it covers a smaller area and is warmer.
During winter, the same amount of heat energy covers a larger area and is colder.

17. Summer – June 21st – September 20th June 21st – Summer Solstice
Dates of the Seasons
Summer – June 21st – September 20th
June 21st – Summer Solstice
Summer Solstice – Date Sun appears highest in the sky.
Fall – September 21st – December 20
September 21st – Autumnal Equinox
Equinox – Equal nights. Daylight and nighttime hours both last 12 hours.

18. Winter – December 21st – March 20th December 21st – Winter Solstice
Dates of the Seasons
Winter – December 21st – March 20th
December 21st – Winter Solstice
Winter Solstice – Date Sun is lowest in the sky.
Spring – March 21st – June 20th
March 21st – Vernal Equinox

19. Throughout the year, the Sun appears to change position in the sky.

20. This is called an analema.
The Sun appears to make a figure 8 in the sky.
This is called an analema.

21. The second factor that affects our seasons is the number of daylight hours.

22. When the Earth is tilted towards the Sun (summer), more of the Northern Hemisphere is in daylight.

23. The North Pole has daylight for 24 hours.
The South Pole has darkness for 24 hours.

24. When the Earth is tilted away from the Sun (winter), less of the Northern Hemisphere is in daylight.

25. The North Pole has darkness for 24 hours.
The South Pole has daylight for 24 hours.

26. Daylight hours (winter) are shorter because most of the Northern Hemisphere spends more time in darkness.

27. Daylight hours (spring/fall) are equal to nighttime hours throughout the world.

28. Seasons are reversed in the Northern and Southern Hemispheres!
One last season fact!
Seasons are reversed in the Northern and Southern Hemispheres!
When it is summer in the Northern Hemisphere, it is winter in the Southern Hemisphere.
When it is winter in the Northern Hemisphere, it is summer in the Southern Hemisphere.

29. Summer
Winter

30. Fall
Spring

31. Winter
Summer

32. Spring
Fall

33. Review I
Review II
Why is Summer Hot?

34. The Presentation ends here.