1. Space Unit
EARTH

2. Earth’s Shape
The Earth is not a true circle, it is a: Oblate Spheroid Bulges in the middle

3. Why Does Earth Have Life?
1. Right distance from the Sun 2. Right amount of water 3. Right amount of atmosphere

4. Earth’s Rotation
The rotation of the Earth lasts for 23hr 56min 4sec. A rotation is the Earth turning around itself. sOJ0G1psUA s/imagerecords/57000/57760/rotate_3 20.mpg

5. Earth’s Revolution
A revolution is the path the Earth takes in the solar system around the Sun. th_science/terc/content/visualizations /es0408/es0408page01.cfm UYaIQNjAX_8

6. Earth’s Revolution
The revolution of the Earth around the Sun takes days. (which is why we have a leap year every 4 years) Next Leap Year: 2020

7. Earth’s Tilt
The Earth is NOT perfectly vertical. It’s tilted! 23.4 degrees.

8. Earth’s Tilt
Not only is the Earth tilted but it wobbles!! sion

9. Precession in action

10. Changing North Star
The wobble changes which star is our North Star (Polaris to Vega) This takes 26,000 years

11. Earth’s Tilt and Seasons
The tilt of the Earth and the Earth’s revolution are the reason we have seasons.

12. Seasons
The seasons are a result of two things:
The tilt of the Earth
Earth’s location in its revolution around the Sun

13. Seasons

14. Seasons - Spring
Vernal Equinox (equinox=equal) March 21st Equally 12 hrs of light and 12 hrs of night.

15. Seasons- Summer
Summer Solstice June 21st 16hrs of light and 8 hrs of night.

16. Seasons-Fall
Autumnal Equinox September 21st 12 hrs of light and 12 hrs of night.

17. Seasons- Winter
Winter Solstice December 21st 8 hrs of light and 16 hrs of dark

18. Seasons
If we did not have a tilt in the Earth we would not have seasons. What would that be like? seasons-change-space.html ogallery/index.html?media_id=

19. solstice
 sun is at its greatest distance from the 
celestial equator 

20. http://astro.unl.edu/naap/motion1/ animations/seasons_ecliptic.swf