Chapter 1: Introduction to
Earth
Introduction to Earth
• Physical earth is dynamic and constantly
changing – never static
– Everything is connected to everything else
• Processes
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Fast
Slow
Large
Small
Regular
Irregular
Geography as a
Field 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?”
Elements of Geography
• Interrelationships
among elements
• Physical
– Examines Earth
elements which
are natural in
origin
• Cultural (Human)
– Looks at elements
of human
endeavor
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 spheres
1.
2.
3.
4.
atmosphere—“air”
lithosphere—“stone”
hydrosphere—“water”
biosphere—“life”
1
2
4
3
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 mass
Figure 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
The Geographic Grid
• Latitudes
– 7 important latitudes:
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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)
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
1.
• 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
3.
– Varies by day/season
• Omaha: ~25° in Dec; ~72 ° in June
1. Solar altitudes at 50 N (Canadian-US border)
2. Solar altitudes at equator
3. Solar altitudes at South Pole
2.
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
The Annual March of the
Seasons
The Annual March of the Seasons
• Significance of seasonal patterns
23½º N
Latitude
– Spread of solar
rays over small
& large areas
– Tropical
latitudes
consistently
warmer
– Polar latitudes
consistently
cooler
– Large seasonal
variations in
temperature in
midlatitudes
June 21
Sept. 21
0º
Mar. 21
Mar. 21
23½º S
Dec. 21
Time
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
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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