2. Sphere  Round three – dimensional object  Surface same distance from its center point  Earth PROOF: ○ Aristotle saw curved shadow of earth on moon ○ Columbus – watched ship sail over horizon and tops of ships sank over horizon last ○ Today – pictures from satellites

3. Oblate Spheroid  Flattened at poles  Bulging at equator  Why: Speed of rotation causes the poles to pull in and the mass at the equator to bulge slightly out

4. Earth’s rotation  Rotation – spinning on an axis  Axis – imaginary pole through earth Tilted 23 ½ ⁰  One spin= 1 day Actual 23hr 56 min Rotation – clockwise ○ Why sun rises in the east and sets in the west

5. Earth’s magnetic field  Created by; Rotation Movement of Fe Ni core Molten mantle  Protects us from solar radiation  Magnetic axis is not the same as the geographical axis

6. Solar ejections and earth’s magnetic field

7. Aurora borialis

10. Aurora australis

13. Earth’s revolution  Revolution – movement of earth in its orbit around the sun  365 ¼ days  Orbit – ellipse Elongated closed curve Two foci points Sun is one of the foci Average 93 million miles

14. 2009 February 18

15.  Perihelion – pt in orbit closest to sun  - Jan 2  -92 million mi  Aphelion – pt in orbit furthest from the sun  - July 2  - 95 million mi

16. Cause of earth’s seasons  Tilt of axis  Position in orbit  Curvature of earth’s surface – amt of solar radiation

17.  Summer Tilt toward sun Direct rays on Tropic of Cancer More concentration of solar radiation Summer solstice – June21 or 22 Longest day of the year

18.  Winter Tilt away from sun Direct rays on Tropic of Capricorn less concentration of solar radiation Winter solstice Dec 21 or 22 Shortest day of the year

19.  Spring and Fall  Direct rays fall on the equator  No tilt toward or away from sun  Equinox – equal nights  Fall – Sept 22 or 23  Spring – March 20 or 21