1. The Reason for Seasons Objectives: Explain why we have day and night.
Explain why we have seasons

2. Motion of Planets Planets rotate and revolve.
Rotation: the spin on the planets axis.
The Earth takes 24 hours to rotate.
The Sun appears to rise and set because the Earth is spinning.
Revolution: the orbit around the sun.
The Earth takes days to orbit the Sun.
The reason we have seasons is due to the Earth’s tilt (23.5º).

3. Day vs. Night

4. Rotation vs. Revolution

5. Earth’s Tilt
Earth’s axis is tilted 23.5° from vertical when compared to its orbit around the Sun
This causes each of Earth’s hemispheres to point towards or away from the Sun during its revolution around the Sun

6. Seasons
When the Northern hemisphere is pointed towards the Sun, we get more direct (spread over a small area) sunlight, giving us summer
When the Northern hemisphere is pointed away from the Sun, we get indirect (spread over a larger area) sunlight, giving us winter

7. Summer and Winter

8. Seasons

9. Solstices Winter solstice
When the Northern hemisphere is pointed directly away from the Sun
Is the shortest day of the year
Summer solstice
When the Northern hemisphere is pointed directly towards the Sun
Is the longest day of the year

10. Solstices

11. Equinoxes When the Earth’s poles are not facing the Sun directly
Day and night are of equal length
Happens twice a year – Spring (Vernal) Equinox and Autumn (Autumnal) Equinox

12. Equinoxes

13. Solstices & Equinoxes
Earth's Revolution Around the Sun

14. Geocentric Model
2000 years ago, Ptolemy believed that the Sun and the planets revolved around the Earth. This is the geocentric model.

15. Geocentric Model

16. Heliocentric Model
Copernicus ( ) proposed a model of the Solar System with planets revolving around the Sun. In the early 1600s Galileo investigated planets with moons orbiting them to confirm that the geocentric model was incorrect. Kepler added the idea that planets travel in ellipses around the Sun not circular pathways.

17. Heliocentric Model

18. Your Task Read page 320 – 328 Define: 1) Orbital Radius
2) Gravitational Force
3) Solstice
4) Equinox
5) Lunar Cycle
6) Eclipse
7) Tides
Complete #1-3, 5, 8, 9-11