Size and shape of earth
•	Equatorial circumference ~ 24,901 miles
–	Equatorial radius ~ 13 miles greater than polar radius….why?
•	Centrifugal force causing polar flattening
–	Thus Earth an oblate spheroid

Latitude
•	Latitude (parallels)
–	E-W circles drawn around earth (measure N-S); perpendicular to axis of rotation 
–	Equator = 0o; 90o = poles (0-90N; 0-90S)
–	Angular measurement

Longitude
•	Longitude (meridians)
–	N-S circles; measure E-W
–	Prime Meridian 0o
•	International Date Line- 180o
–	Each line 
•	Go thru poles
•	Cut earth in half
–	0-179oE, 0-179oW

Seasons, Earth tilt
•	Earth tilted 23.5o from the perpendicular
–	Why we have seasons…
•	So, what is the significance of the Tropics (Cancer, Capricorn) and Arctic and Antarctic Circles?
–	Tropic of Cancer = farthest north that suns rays will be directly (90o) overhead
–	T of Capricorn = farthest south that suns rays will be directly (90o) overhead
–	Arctic Circle = farthest south (in NH) with 24 hrs day or nite
–	Antarctic Circle = farthest north (in SH) with 24 hrs day or nite
•	The Equator? Equinoxes?
–	Equator always has 12hr of day/nite
–	On Equinoxes, everywhere has 12hr of day/nite (as if Earth were straight up/down with respect to plane of ecliptic)

Effect on temperature, climate
•	With tilt, amounts of solar energy receipt on Earth varies (in form of daylength, winter/summer length)
–	amount of energy dispersed differently throughout day/year