1

Earth DimensionsEarth Dimensions

2

The Earth is an oblate The Earth is an oblate spheroid.spheroid.

That is a sphere with slightly That is a sphere with slightly flatten poles and a slight flatten poles and a slight bulging at the equatorial bulging at the equatorial region.region.

3

This means the polar This means the polar circumference (40,008 km) is circumference (40,008 km) is 68 km smaller than the 68 km smaller than the equatorial circumference equatorial circumference (40,076 km).(40,076 km).

4

A. Evidence for the Earth A. Evidence for the Earth shape comes from several shape comes from several sources.sources.

5

1. Early sailors noticed that 1. Early sailors noticed that ships seem to "disappear" as ships seem to "disappear" as they sail out of port over the they sail out of port over the horizon.horizon.

6

However it is the altitude of However it is the altitude of Polaris that provides the Polaris that provides the earliest proof.earliest proof.

Polaris (the North Star) is Polaris (the North Star) is directly overhead of the North directly overhead of the North Pole and has an altitude of 90Pole and has an altitude of 90⁰⁰..

7

At the equator, the altitude At the equator, the altitude of Polaris is 0of Polaris is 0⁰⁰ (it is located (it is located on the horizon).on the horizon).

As you head north the As you head north the altitude of Polaris increases, altitude of Polaris increases, and is in fact equal to the and is in fact equal to the latitude.latitude.

8

That the That the altitude of altitude of

Polaris and Polaris and an observers an observers latitude are latitude are the same.the same.

9

Finding PolarisFinding Polaris

Finding Polaris can be done using Finding Polaris can be done using the "pointer" stars in the Big the "pointer" stars in the Big Dipper (Ursa Major). Dipper (Ursa Major).

Facing Polaris, points you North, Facing Polaris, points you North, measuring the angle to Polaris tells measuring the angle to Polaris tells you your latitude in the Northern you your latitude in the Northern HemisphereHemisphere

10

11

2. Photographs from 2. Photographs from space confirm earth's space confirm earth's oblate shape.oblate shape.

12

3.3. Careful measurements Careful measurements of a known mass shows of a known mass shows that the mass' weight is that the mass' weight is heavier at the poles heavier at the poles than at the equator. than at the equator.

13

B. How to determine the size B. How to determine the size of Earth?of Earth?

Modern methodsModern methods Photographs from Photographs from

spacespace Measurements of Measurements of

Polaris (North Star)Polaris (North Star) Non-modern methodsNon-modern methods

Eratosthenes Eratosthenes methodmethod

14

Eratosthenes Eratosthenes

Greek mathematician Greek mathematician Lived approximately 2 x 10Lived approximately 2 x 1033 years ago in years ago in

EgyptEgypt Used geometry to calculate the circumference Used geometry to calculate the circumference

of Earthof Earth

15

Assumptions Eratosthenes Assumptions Eratosthenes mademade

1. All rays of the sun approach Earth in 1. All rays of the sun approach Earth in a parallel mannera parallel manner

sunEarth

Rays of light

16

Assumptions Eratosthenes Assumptions Eratosthenes made (cont.)made (cont.)

2. Earth is a perfect sphere2. Earth is a perfect sphere He was almost correctHe was almost correct

17

Geometry that Eratosthenes Geometry that Eratosthenes usedused

Alternate interior angles made by parallel lines of the sun’s rays are equal

sun sun raysa

b

angle a = angle b

18Earth’s center

Sun’s rays

sun = Alexandria

= Syene

Distance between Alexandria and Syene was 925 km

Shadow angles = 7.2°

19

How to find circumference?How to find circumference?

Use the information from the experiment to set up a proportion (2 equal ratios)

Distance (km) Shadow AngleCircumference = 360°of Earth (km)

925 kmCircumference of Earth (km)

=7.2°360°

crossmultiplyto solve

20

925 km x 360° = circumference x 7.2°

925 km x 360°= circumference

7.2°

46, 250 km = circumference of Earth( very close to the actual measurement)

21

C. The Outer Parts of the C. The Outer Parts of the Earth.Earth.

22

Hydrosphere – the portion Hydrosphere – the portion of the earth that contains of the earth that contains earth's water.earth's water.

This includes the (lower) This includes the (lower) atmosphere, surfaceatmosphere, surface, and upper , and upper layer of the lithosphere.layer of the lithosphere.

23

2.2. AtmosphereAtmosphere – the – the sphere of gasphere of gases that ses that surround the earth. surround the earth.

The Atmosphere is layered, or divided The Atmosphere is layered, or divided into four zones based on temperature. into four zones based on temperature.

The lowest, the troposphere contains The lowest, the troposphere contains most of the gases that we need to most of the gases that we need to survive and our weather. survive and our weather.

The other three layers are the The other three layers are the Stratosphere, MesospStratosphere, Mesosphere, and here, and Thermosphere.Thermosphere.

See Reference TableSee Reference Table

24

3.3. LithosphereLithosphere (geosphere)– the outer (geosphere)– the outer most layer of the earth. most layer of the earth.

Approximately 100 km Approximately 100 km thick, the thick, the lithosphere is the portion of the lithosphere is the portion of the crust and mantle that contain the crust and mantle that contain the plates which move around forming plates which move around forming earth's features.earth's features.

25

Using a compassUsing a compass

A compass will not show True A compass will not show True North (geographic north), but North (geographic north), but rather Magnetic North, because rather Magnetic North, because earth's magnetic field is tilted at earth's magnetic field is tilted at 1212⁰ ⁰ angle to the Earth's axis of angle to the Earth's axis of rotationrotation