1. Lesson 3 The Third Rock from the Sun! (Continued)

2. Think About It… How would Earth be different if it did not rotate on its axis?

3. Earth’s Rotation… Day and night are caused by… Day and night are caused by… The rotation of the Earth on its axis The rotation of the Earth on its axis Earth spins… Earth spins… 15 degrees each hour 15 degrees each hour There are 360 degrees in a circle (the circumference of Earth). There are 360 degrees in a circle (the circumference of Earth). 360 divided by 15 is 24 so there are 24 hours in a day! 360 divided by 15 is 24 so there are 24 hours in a day!

4. Earth’s Rotation… The exact amount of time it takes Earth to spin one time on its axis is… The exact amount of time it takes Earth to spin one time on its axis is… 23.9345 hours 23.9345 hours If an Earth day was 5832.5 hours long (like that of Venus!) then… If an Earth day was 5832.5 hours long (like that of Venus!) then… It would take 243 days for Earth to spin one time on its axis! It would take 243 days for Earth to spin one time on its axis! Our day and night would be much longer! (It’d get really hot and really cold!) Our day and night would be much longer! (It’d get really hot and really cold!)

5. Earth’s Rotation… The exact amount of time it takes Earth to spin one time on its axis is… The exact amount of time it takes Earth to spin one time on its axis is… 23.9345 hours 23.9345 hours If an Earth day was 5832.5 hours long (like that of Venus!) then… If an Earth day was 5832.5 hours long (like that of Venus!) then… It would take 243 days for Earth to spin one time on its axis! It would take 243 days for Earth to spin one time on its axis! Our day and night would be much longer! (It’d get really hot and really cold!) Our day and night would be much longer! (It’d get really hot and really cold!)

6. Earth’s Rotation and Its Shape… Earth’s rotation causes it to take the shape of an oblate spheroid. Earth’s rotation causes it to take the shape of an oblate spheroid. As Earth rotates on its axis, centrifugal force causes the Earth’s mass to move away from its center at the equator where this force is greatest. As Earth rotates on its axis, centrifugal force causes the Earth’s mass to move away from its center at the equator where this force is greatest. There is a slight bulging at the equator and a slight squishing at the poles. There is a slight bulging at the equator and a slight squishing at the poles. See next slide! See next slide!

7. Earth’s Rotation and Its Shape… Simulation: http://www.cleonis.nl/physics/phys256/equatorial_bulge.phphttp://www.cleonis.nl/physics/phys256/equatorial_bulge.php

8. Earth’s Rotation and Its Shape… http://www.cleonis.nl/physics/phys256/equatorial_bulge.php

9. Earth’s Orbit and Seasons… The ecliptic is… The ecliptic is… the plane in which Earth orbits around the Sun the plane in which Earth orbits around the Sun http://en.wikipedia.org/wiki/Ecliptic

10. Earth’s Orbit and Seasons… Remember, Earth’s axis is… Remember, Earth’s axis is… the imaginary line that cuts through the north and south poles. the imaginary line that cuts through the north and south poles. The tilt of Earth’s axis relative to the ecliptic is 23.5 degrees. The tilt of Earth’s axis relative to the ecliptic is 23.5 degrees. http://republicanredefined.com/2010/03/02/chile-quake-shifted-earths-axis-and-made-days-shorter/

11. The Seasons! http://www.exploratorium.edu/ancientobs/chaco/HTML/TG-shadows.html

12. The Seasons! What causes summer in the northern hemisphere? What causes summer in the northern hemisphere? when it is tilted toward the Sun during Earth’s orbit when it is tilted toward the Sun during Earth’s orbit What causes winter in the northern hemisphere? What causes winter in the northern hemisphere? when it is tilted away from the Sun during Earth’s orbit when it is tilted away from the Sun during Earth’s orbit

13. The Seasons! The seasons in the northern and southern hemispheres are… The seasons in the northern and southern hemispheres are… opposites! opposites!