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
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
Earth’s rotation Rotation – spinning
on an axis Axis – imaginary
pole through earthTilted 23 ½ ⁰
One spin= 1 dayActual 23hr 56 minRotation – clockwise
○ Why sun rises in the east and sets in the west
Earth’s magnetic field Created by;
RotationMovement of Fe Ni
coreMolten mantle
Protects us from solar radiation
Magnetic axis is not the same as the geographical axis
Earth’s revolution Revolution –
movement of earth in its orbit around the sun
365 ¼ days Orbit – ellipse
Elongated closed curve
Two foci pointsSun is one of the fociAverage 93 million
miles
2009 February 18
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
Cause of earth’s seasons Tilt of axis Position in orbit Curvature of earth’s
surface – amt of solar radiation
SummerTilt toward sunDirect rays on Tropic
of CancerMore concentration of
solar radiationSummer solstice –
June21 or 22Longest day of the
year
WinterTilt away from sun Direct rays on Tropic
of Capricorn less concentration of
solar radiationWinter solstice Dec
21 or 22Shortest day of the
year