Chapter 1: Introduction to Earth. Introduction to Earth Physical earth is dynamic and constantly changing – never static –Everything is connected to everything.

Chapter 1: Introduction to Earth

Introduction to Earth

• Physical earth is dynamic and constantly changing – never static– Everything is connected to everything else

• Processes– Fast– Slow– Large– Small– Regular– Irregular

Geography as aField of Learning

• Greek Meaning - “earth description”– Fundamental questions:

• “Why is what where?”• “So what?”

• Spatial Distributions• What is Physical Geography?

– Distribution & explanation of processes & features of natural origin

– How/why physical processes have shaped Earth’s surface

• “Why the earth is the way it is”

“Where are the four corners of the earth?”

• Interrelationships among elements

• Physical– Examines Earth

elements which are natural in origin

• Cultural (Human)– Looks at

elements of human endeavor

Elements of Geography

Science and Geography

• The Scientific Method– Observe phenomena– Formulate a hypothesis

• Design an experiment• Predict the outcome of

the experiment• Conduct the experiment

– Draw conclusions• Theory

• Scientific “proof”

The Environmental Spheres

• Physical earth is dynamic & constantly changing• Break the real world up into parts to better understand it.

– Simplified parts = systems (spheres)

• Everything is connected to everything else

• Four primary spheres1. atmosphere—“air”

2. lithosphere—“stone”

3. hydrosphere—“water”

4. biosphere—“life”

2 3

1

4

Interactions between the spheres

The Solar System

• Formation of the Solar System– Formed 4.5-5 billion years ago– 8 planets

• 4 terrestrial planets • 4 gas giants

• Sun– Medium sized star– Makes up over 99% of the

solar system’s massFigure 1-4

The Size and Shape of the Earth

• Earth’s Physical Characteristics

• Not perfectly round– Oblate spheroid– Equatorial diameter

~ 12,756 km– Polar diameter

~ 12,714 km– Circumference of

40,000 km

Figure 1-7

The Size and Shape of the Earth

• Maximum relief– Mt. Everest = 29,035 ft.– Mariana Trench = 36,198 ft.

• Surface differences– Land = 29%– Oceans = 71%– Northern Hemisphere: “Land

Hemisphere” (39% land)– Southern Hemisphere: “Water

Hemisphere” (19% land)

Figure 1-6

The Geographic Grid

• Location on Earth– Need an accurate location on Earth to describe geographic

features– Use Earth’s rotation axis to base location on the surface– North Pole and South Pole– Plane of the Equator

• Halfway between poles & perpendicular to Earth’s surface

– Graticule

Figure 1-9

The Geographic Grid

• Great Circles– Cuts the sphere into 2 equal

halves (hemispheres)– Must pass through the

sphere’s center– Example: Circle of

illumination– Small circles

Figure 1-10

The Geographic Grid

• Latitudes– 0º-90º N/S– Parallels

• Connects points of equal latitude

• 69 miles or 111 km apart

– Angle north or south of the equator

Figure 1-11

• Latitudes– 7 important latitudes:

– Tropic of Cancer (23.5° N)– Tropic of Capricorn (23.5° S)– Equator (0°)– North Pole (90° N)– South Pole (90° S)– Arctic (66.5° N)– Antarctic Circles (66.5° S)

The Geographic Grid

Figure 1-12

The Geographic

Grid• Longitudes

– 0°-180° E/W– Meridians– Prime Meridian (0°

longitude) located at Greenwich, England

• Longitude is measured E/W of this point

– Angle east or west of the Prime Meridian

– Converge at the poles• Not parallel to one another

Figure 1-16

Earth-Sun Relations

• Rotation of the Earth– 24 hours for 1 rotation

• Rotation velocity varies with latitude– At Equator = 1037 mph– At Poles = 0 mph

– Rotation is counterclockwise relative to North Pole (West to East)

– Rotational influences• Diurnal transition from light to

darkness (daylight/darkness)• Tidal effects from Moon & Sun• Coriolis Effect Figure 1-18

Earth-Sun Relations

• Earth’s Revolution around Sun– One revolution takes

365 ¼ days• 365 days, 5 hrs,

48 min, & 48 sec • (365.242199 days)• Leap Year

– Elliptical orbit– Aphelion

– During N. Hemisphere summer (~July 4)

– Perihelion– During N. Hemisphere winter (~Jan 3)

– Perihelion/Aphelion are NOT important factors in seasonal variations

Figure 1-19

Earth-Sun Relations

• Orbital Properties– Plane of the Earth’s orbit is the

plane of the ecliptic– Inclination

• Earth’s axis tilted at 23.5°

– Plane of ecliptic is not parallel to equatorial plane

• Polarity of Earth’s axis– Parallelism

• North Pole always points toward Polaris (“North Star”)

Figure 1-20

Circle of Illumination

• Because Earth is a sphere, only 50% can be illuminated by the sun at once

• If the axis was perpendicular to the sun’s rays, all points on earth would have 12 hours of daylight/darkness each day

• Because of Earth’s tilt, most places experience varying amounts of daylight & darkness throughout the year

Solar Declination & Solar Altitude

• Solar Declination: latitude where sun’s rays strike earth at 90° angle– 23.5 N to 23.5 S (Tropics)

• Solar altitude: angle sun’s rays hit Earth at noon– Only 1 pt on earth receives Sun’s direct

rays at a time– 0 when sun is on horizon – 90 when sun is directly overhead– Varies by day/season

• Omaha: ~25° in Dec; ~72 ° in June

1.

2.

3.

1. Solar altitudes at 50 N (Canadian-US border)2. Solar altitudes at equator

3. Solar altitudes at South Pole

Analemma

• Figure-8 shaped scale to determine latitude of the vertical rays of noon sun for every day

• 2 main purposes:– Determine solar altitude

(angle of the noon sun above the horizon)

– Shows fluctuations in the arrival of the overhead sun

Changes in Daylight

• All locations spend 50% of time in daylight & 50% in darkness• Daylight equally distributed every day at equator

– Distribution becomes more unequal as you move poleward

• Period of daylight varies throughout the year– Shortest day about Dec 21

(Winter solstice)– Longest day about June 21

(Summer solstice)– Opposite in Southern Hemisphere

• Day length & solar angle of sun’s rays determine amount of insolation received at any location

The Annual March of the Seasons

• Three important conditions– Declination of the Sun– Solar altitude– Length of day

• Two solstices– June solstice– December solstice

• Two equinoxes– March equinox– September equinox Figure 1-22

The Annual March of the Seasons

• June solstice– Approximately June 22– Sun is directly overhead

at 23.5° N latitude (Tropic of Cancer)

– Antarctic Circle (66.5° S) to South Pole (90° S) in 24 hours of darkness

– Arctic Circle (66.5° N) to North Pole (90° N) in 24 hours of daylight

Figure 1-22

The Annual March of the Seasons

• December solstice– Approximately December 22– Sun is directly overhead

at 23.5° S latitude (Tropic of Capricorn)

– Arctic Circle (66.5° N) to North Pole (90° N) in 24 hours of darkness

– Antarctic Circle (66.5° S) to South Pole (90° S) in 24 hours of daylight

Figure 1-22

The Annual March of the Seasons

• Equinoxes– Approximately March

21 & September 21– Day length is 12 hours

worldwide (“equinox”)– Sun is directly

overhead at the equator

Figure 1-22

The Annual March of the Seasons

• Day length– Always 12 hours at the

equator– In the Northern Hemisphere,

day length increases after March equinox

– Maximum day length during June solstice in Northern Hemisphere

– Opposite for Southern Hemisphere

SP

NP

0º

40º N

15h n9h d

Circle of illumination

(C.i.)

23½ºS

66½º N – Arctic Circle 24h n

23½º S – Tropic of Capricorn

66½º S – Antarctic Circle 24h d

0º - C.i. bisects

12h n12h d

Direct (90º) Rays

66½º N24h n

66½º S

24 h d

– 4 Key Days - Day 1: Dec. 21 – Winter Solstice in N.H.

= 90º - (40 +/- 23½)

SP

NP

0º

40º N

15h n9h d

23½º S

12h n12h d

+ = 90º - 63½ = 26 ½ º

66½º S

24h d

LP is Latitude of PlaceLS is Latitude of Sun

ANS = 90º - (Arc b/t LP & LS)

66½º N24h n

Direct (90º) Rays

– Dec. 21 (cont.)

Direct (90º) Rays

SP

NP= 90º - (40 - 0)= 90º - 40 = 50º

0º

66½º S

66½º N

40º N12h d

12h d

12h d

12h n

12h n

12h n

ANS = 90º - (Arc b/t LP & LS)

– Day 2: Mar. 21 – Spring Equinox in NH

SP

NP

0º

Direct (90º) Rays

66½º S

66½º N

40º N23½º N

= 90º - (40 - 23½ )= 90º - 16½ = 73½ º

15h d9h n

24h n

24h d

ANS = 90º - (Arc b/t LP & LS)

23½º N – T. of Cancer

– Day 3: June 21 – Summer Solstice in NH

Direct (90º) Rays

SP

NP

0º

66½º S

66½º N

40º N

40º S

ANS = 90º - (Arc b/t LP & LS)= 90º - (40 - 0)= 90º - 40 = 50º

12h d

12h d

12h d

12h n

12h n

12h n

– Day 4: Sept. 21 – Fall Equinox in NH

The Annual March of the Seasons

Latit

ude

23½º N

23½º S

0º

Time

Dec. 21

Sept. 21

Mar. 21

June 21

Mar. 21

The Annual March of the Seasons

– Spread of solar rays over small & large areas

– Tropical latitudes consistently warmer

– Polar latitudes consistently cooler

– Large seasonal variations in temperature in midlatitudes

• Significance of seasonal patterns

Telling Time

• 3 physical measures of time– Tropical year– Lunar month– Solar day

• Solar noon– Sun casts the shortest shadow

• Ante-meridian (AM—“before noon”)• Post-meridian (PM—“after noon”)

Figure 1-23

Telling Time

• Current time system (24 time zones)– 1 Earth day = 24 hours & 1 full Earth rotation = 360°– Time zones are

15° or 1 hour apart

• Ex: 2 points 1 hour apart = 15° apart

• Ex: 2 points 15° apart = 1 hour apart

Figure 1-24

Telling Time

• Current time system– Greenwich Mean Time (GMT) is standard– Prime meridian 0° longitude– Universal Time

Coordinated (UTC)

– 180° meridian = International Date Line– Cross going east ,

go to preceding day– Cross going west,

go to next day

Figure 1-24

Telling Time

• Daylight-saving time– Move clocks ahead by an

hour during the summer months

– Originally done by Germans during WWII; now practiced by many nations

– Conserves lighting energy by providing an extra hour of daylight

Figure 1-25

Summary

• Geography is the study of the distribution of physical and cultural attributes of Earth• Many sciences have branched off of geography• The scientific method is important when doing scientific studies• Earth has four primary spheres: the atmosphere, the lithosphere, the hydrosphere,

and the atmosphere• The solar system formed 5 billion years ago and consists of 8 planets• Earth is an imperfect sphere• A latitude and longitude grid help identify locations on Earth’s surface• Earth rotates on its axis in 24 hours• Earth revolves around the Sun in 365 ¼ days• Tilt of Earth’s axis causes seasons• Equinoxes and solstices help identify when a seasonal transition occurs• Time zones were established to have a uniform global time system• Daylight-saving time was devised to conserve energy by adding an hour of daylight