1. Earth Rotation

3. Day and Night For a very long time people thought the Sun and Stars moved around the Earth. For a very long time people thought the Sun and Stars moved around the Earth. So Day and Night were caused by the Sun coming up over the horizon or setting below the horizon. So Day and Night were caused by the Sun coming up over the horizon or setting below the horizon. It appeared to move from East to West. It appeared to move from East to West.

4. Day and Night We now know the Sun is not moving and the Earth is rotating. We now know the Sun is not moving and the Earth is rotating. The apparent East – West motion of the Sun is caused by the Earth rotating from West to East. The apparent East – West motion of the Sun is caused by the Earth rotating from West to East.

5. Evidence Either explanation of the Sun’s motion could be correct. Either explanation of the Sun’s motion could be correct. We need evidence to support rotation. We need evidence to support rotation.

6. Evidence We have already discussed the Coriolis Effect. We have already discussed the Coriolis Effect. If the Earth did not rotate there would be no deflection of winds or moving objects. If the Earth did not rotate there would be no deflection of winds or moving objects.

7. Evidence Another piece of evidence is movement of a pendulum. Another piece of evidence is movement of a pendulum. http://www.calacademy.org/products/pen dulum/page1.htm http://www.calacademy.org/products/pen dulum/page1.htm http://www.calacademy.org/products/pen dulum/page1.htm http://www.calacademy.org/products/pen dulum/page1.htm

8. Evidence http://www.classzone.com/books/earth_sc ience/terc/content/visualizations/es0403/e s0403page01.cfm?chapter_no=visualizatio n http://www.classzone.com/books/earth_sc ience/terc/content/visualizations/es0403/e s0403page01.cfm?chapter_no=visualizatio n http://www.classzone.com/books/earth_sc ience/terc/content/visualizations/es0403/e s0403page01.cfm?chapter_no=visualizatio n http://www.classzone.com/books/earth_sc ience/terc/content/visualizations/es0403/e s0403page01.cfm?chapter_no=visualizatio n

9. Evidence Because of satellite images we can now actually see the rotation of the Earth. Because of satellite images we can now actually see the rotation of the Earth.

10. Evidence http://www.classzone.com/books/earth_sc ience/terc/content/visualizations/es0404/e s0404page01.cfm?chapter_no=visualizatio n http://www.classzone.com/books/earth_sc ience/terc/content/visualizations/es0404/e s0404page01.cfm?chapter_no=visualizatio n http://www.classzone.com/books/earth_sc ience/terc/content/visualizations/es0404/e s0404page01.cfm?chapter_no=visualizatio n http://www.classzone.com/books/earth_sc ience/terc/content/visualizations/es0404/e s0404page01.cfm?chapter_no=visualizatio n

11. Day Length A day by definition is the length of time it takes a planet to make one complete rotation. A day by definition is the length of time it takes a planet to make one complete rotation. Most people will tell you that a day on Earth is 24 hours. Most people will tell you that a day on Earth is 24 hours.

12. Day Length Sunrise on 4/4/06 is 6:33 Sunrise on 4/4/06 is 6:33 Sunrise on 4/5/03 is 6:31 Sunrise on 4/5/03 is 6:31 That makes the day 23hours and 58 minutes long. That makes the day 23hours and 58 minutes long. Sunrise on 4/6/06 is 6:30 Sunrise on 4/6/06 is 6:30 That gives you a day of 23hours 59 minutes. That gives you a day of 23hours 59 minutes. On 4/7 – 6:28 day length of 23hr 58min. On 4/7 – 6:28 day length of 23hr 58min.

13. Day Length If you observe the time from sunrise to sunrise it varies greatly over the year. If you observe the time from sunrise to sunrise it varies greatly over the year.

15. Day Length The ups and down come close to balancing out so we get what we call a Mean Solar Day of 24 hours. The ups and down come close to balancing out so we get what we call a Mean Solar Day of 24 hours. If we use a star as a marker the day length does not change. If we use a star as a marker the day length does not change. This is called a Sidereal day and is 23 hours 56 minutes and 4.091 seconds. This is called a Sidereal day and is 23 hours 56 minutes and 4.091 seconds.