1. Motions and Their Effects
Seasonal Change and Planetary Movement

2. Seasons
The tilt of the Earth’s axis is 23.5 degrees
This tilt causes seasonal changes

3. Winter Solstice
December 21 or 22
North Pole in darkness for 24 hours
South Pole has continual daylight
Sun is at its lowest point

4. Why do we have winter?
Fewer hours of sunlight during the day
North pole is tilted away from the sun
Light rays are less direct

5. Vernal Equinox (equal)
March 20 or 21 (Spring)
Sun is directly over the equator
Every part of the Earth experiences equal hours of day and night

6. Summer Solstice
June 20 or 21
South Pole in Darkness
North Pole in Light
Sun appears at its highest point

7. Why we have summer?
Daylight hours are longer
Sunlight is more direct

8. Autumnal Equinox (equal)
September 22 or 23 (Fall)
Equal hours of day and night
Sun is directly over the equator

9. Questions
How many months apart are the solstices and the equinoxes?
How is the vernal equinox similar to the autumnal equinox?

10. Questions
What are the differences between the summer and the winter solstices?
Why do we have changes in seasons during the year?

11. Kepler
Each planet moves in an elliptical orbit (stretched out circle)
Planets speed up their orbit as they approach the Sun and slow down as they move away from it

12. Questions
What was Kepler’s contribution to the understanding of planetary movement?
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