the earth is a rotating sphere - msu billings 2009/suits/geog... · the earth is a rotating sphere...

The Earth is a Rotating Sphere

• The Shape of the Earth

• Earth’s Rotation ( and relative movement of the Sun and Moon)

• The Geographic Grid

• Map Projections

• Global Time

• The Earth’s Revolution around the Sun

Earth

The Shape of the Earth

the Earth’s shape is very

close to spherical (oblate

ellipsoid (flattened at the

poles)

Dpolar = 7900 miles

= 12,714 km

Dequator = 7926 miles

= 12,756 km

Radius [r] = Diameter/2

Circumference of a circle = 2r

Area of a circle = r2

Surface area of a sphere = 4r2

Volume of a sphere = 4/3r3

a

b

c

The Earth’s movement results in daily, monthly,

and annual cycles

Diurnal (day/night) cycles are produced by changes in

sunlight resulting from the Earth’s rotation

Annual cycles result from the revolution of the Earth

about the Sun

Seasonal cycles result from the tilt of the Earth’s

rotational axis

Tidal cycles result from interactions between the Sun,

the Moon and the Earth

But first,

Did ancient mariners think

the world was flat?

The direction of

the Earth’s

rotation is

counterclockwise

when viewed

from above the

north pole or

west to east

when viewed

with the north

pole up

Earth Rotation

The Geographic Grid

Cartography

Earth is an oblate ellipsoid (flattened at the poles)

divided into degrees, 60 minutes and 60 seconds

provides a “grid” of imaginary lines (parallels and

meridians)

IG4

e_

01_0

4

b) Longitude (Meridians) 1 degree

of longitude = 111 km at the

equator and 0 at the poles

The Geographic Grid

a) Latitude (Parallels)

1 degree latitude = a constant 111 km

Figure 1.3, p. 28

Latitude is the angle

between a point on a

parallel and the centre

of the Earth and a

point on the equator

Longitude is the angle

between a point on a

meridian and the

centre of the Earth and

a point on the Prime

Meridian

The Geographic Grid

Figure 1.5, p. 29

The Prime Meridian,

The Greenwich Observatory

London, England

Revolution

• one complete circling around the Sun

• from above north pole in counterclockwise direction

• the path is not circular but is very slightly elliptical

• all planets orbit on the plane of the ecliptic

E

The Earth’s Revolution around the Sun

SUN

Figure 1.14, p. 38

The Earth’s Revolution around the Sun

the Earth and Moon both rotate and revolve in a

counterclockwise direction (when viewed from a point over the

Earth’s north pole)

sun is not in the middle of the plane of the ecliptic

SUNE E

variation in distance of ~ 3%

Aphelion - the Earth

furthest away from Sun

(July 4)

Perihelion - the Earth

closest to Sun

(January 3)

The Earth’s Revolution around the Sun

152 million km 147 million km

The earth’s axis

is tilted

66.5° to the

plane of the

ecliptic

or from the

perpendicular to

the plane of the

ecliptic by 23½°

Earth Rotation

Figure 1.16, p. 40

the Earth rotates about its axis from west to east once every 23

hours and 56 minutes

the Earth’s axis points same way (parallelism) as it revolves

around the sun

The Earth’s Revolution around the Sun

The Earth’s Revolution around the Sun

at equinox, the

circle of

illumination

passes through

both poles

the subsolar

point is the

equator

each location on

Earth

experiences 12

hours of sunlight

and 12 hours of

darkness

Figure 1.18, p. 41

The Earth’s Revolution around the Sun

Solstice (“sun stands still”)

On June 22, the subsolar point is 23½°N (Tropic of Cancer)

On Dec. 22, the subsolar point is 23½°S (Tropic of Capricorn)

Figure 1.19, p. 41

The Earth’s Revolution around the Sun

the latitude

of the

subsolar

point marks

the

sun’s

declination

which

changes

throughout

the

year

Figure 1.20, p. 42

Solstice & Equinox

• Earth's tilt of 23.5° and revolution around the sun creates seasonal solar exposure and heating patterns

• At solstice, tilt keeps a polar region with either 24 hours of light or darkness

• At equinox, tilt provides exactly 12 hours of night and 12 hours of day everywhere

the four seasons occur because the Earth maintains a constant

orientation (tilted 23½° with respect to the perpendicular to the

plane of the ecliptic) as it revolves around the sun

The Earth’s Revolution around the Sun

Figure 1.17, p. 40

http://www.geog.ucsb.edu/~joel/g110_w08/lecture_notes/sun_angle/anim_fall.gif

http://www.geog.ucsb.edu/~joel/g110_w08/lecture_notes/sun_angle/anim_sum.gif

Local Solar ChangesNorthern

hemisphere sunrises are

in the southeast

during winter, but in the

northeast in summer

Summer noon time sun is also higher above the

horizon than the winter

sun

based on the east-west position of the Sun

a solar day defined by one sun circuit

solar noon (at a particular location) is the time of the

highest solar angle

the time is calculated by the position of the Sun at

selected meridians (Standard Time)

Global Time

the Earth rotates 15° per hour so time zones differ by 1 hour

(360°/15° = 24 hours)

Global Time

Figure 1.12, p. 36

Different days are observed on either side of the International

dateline (180th meridian = 15° X 12 hours), 12 hours

difference from the Prime Meridian

Global Time

Figure 1.13, p. 37

To make a map you need a Map Projection

3 properties to consider: scale, area and

shape

Map Projections

Map ProjectionsPolar Projection

centered on north or

south pole

meridians are

radiating straight lines

parallels are

concentric circles

spacing of parallels

(scale fraction)

increases outward

from the pole

Map ProjectionsMercator

Projection

rectangular grid of

meridians (straight

vertical lines) and

parallels (straight

horizontal lines)

meridians are evenly

spaced, spacing of

parallels increases

with latitude

straight line on map

represents true

compass direction

(bearing), i.e. for

navigation

Used to show surface

flows, e.g. weather,

oceans

Map ProjectionsGoode Projection

two sets of mathematical curves used to define its meridians

indicates the true sizes of the Earth’s surface but distorts the shapes of areas

Used to show land features

Figure 1.10, p.32

Modern Cartography and GIS

GIS = Geographic Information System

a computer-based system that allows maps,

diagrams, satellite images and aerial photographs to

be stored and manipulated

uses geographically referenced data (e.g.

projections)

spatially-referenced data can therefore be used to

solve complex planning problems.

Map Projections

GIS data layers: for

each map layer, the

geographic location of a

point on the Earth’s

surface must coincide

(georeferencing)

Example:

Map Projections

p. 35http://ahps2.wrh.noaa.gov/ahps2/index.php?wfo=byz&view=1,1,1,1,1,1,1,1&toggles=10,7,8,2,9,15,6