1. Earth’s Shape, Dimensions and Internal Heat & Density
Chapter 2
Earth’s Shape, Dimensions and Internal Heat & Density

2. The Earth is Spherical
Technically, we call it an “oblate spheroid”, because it is a LITTLE wider at the Equator than at the Poles…but more on that later…

3. Evidence of Earth’s Spherical Shape
Early Evidence…you know, Columbus and those guys….
Mast of a ship is the first to appear over the horizon when it’s traveling towards you, and last to disappear when it’s traveling away
As ships travel towards the North Pole, Polaris (north star) appears to rise higher in the sky each night Super important factoid: the altitude (angle) of Polaris above the horizon is the same # as the Latitude of the observer!
During a lunar eclipse, the earth's shadow that is cast on the moon is in the shape of an arc (only spheres cast circular shadows)
And the #1 evidence in the modern age… SATELLITE PHOTOS

4. The Sphere is NOT Perfect
See… I told you we’d get to it later….
Objects weigh less at the Equator than at the Poles – the Poles are closer to the center of earth and therefore are “pulled” more by earth’s gravity!
Earth is an OBLATE SPHERIOD – it is slightly flattened at the poles and bulges at the Equator

5. The Sphere is NOT Perfect
See… I told you we’d get to it later….
The Mathematical reason why is this…..
Force of Gravity (Fg) = (mass of object 1 (m1)) x (mass of object 2 (m2)) distance squared (d2)
(Fg) = (m1) x (m2) (d2)
So, if your distance from the center of Earth is greater (like at the equator), you are dividing by a bigger # THAT IS SQUARED and the gravitational force pulling between you and the Earth is weaker…so…you weigh less!!!! 

6. BUT...The Earth is STILL Spherical
And the BEST representation of the Earth is STILL a perfect circle….
Think about it – have you ever seen a picture of the Earth from space? It’s a circle isn’t it???

7. this formula is, very simply, a RATIO!!!
Measuring Earth’s Circumference
Eratosthenes’ Formula: (er uh TOS thuh neez)
length of arc = distance on surface
360º circumference
this formula is, very simply, a RATIO!!!
Eratosthenes used the difference in the angle of the sun’s rays at 2 locations directly North and South of one another to calculate Earth’s circumference! (P. 19 in text)

8. Earth’s Dimensions
Remember – Earth bulges at the Equator and is flattened at the Poles!!!
Circumference at the equator: 40,074 km
Circumference at the poles: 40,007 km
Diameter at the equator: 12,756 km
Diameter at the poles: 12,714 km

9. Open your EARTH SCIENCE REFERENCE TABLES (ESRT) to page 10!

10. What conclusions can we make from this diagram????

11. Conclusions:
starting at the Earth’s crust and moving in toward it’s core increases both temperature and density
iron and nickel (core) are considerably more dense than oxygen and silicon (crust)
Density – a measure of the amount of material (mass) in a given space (volume)
density = mass ÷ volume
Understanding density is one of the keys to success in understanding Earth Science!!!!