1. Chapter 1: Introduction to Earth
McKnight’s Physical Geography: A Landscape Appreciation, Tenth Edition, Hess

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Introduction to Earth
Geography as a Field of Learning
Science and Geography
The Environmental Spheres
The Solar System
The Size and Shape of Earth
The Geographic Grid
Earth-Sun Relations
The Annual March of the Seasons
Telling Time
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3. Geography as a Field of Learning
Definition
Sciences which branch from geography
Physical versus cultural
“Why what is where and so what?”
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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
Scientific “proof”
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Science and Geography
Measurement Systems
Need measurement systems to quantify scientific processes
SI versus English units
Conversions
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6. The Environmental Spheres
Four primary spheres
atmosphere—“air”
lithosphere—“stone”
hydrosphere—“water”
biosphere—“life” 1 4 2 3
Interactions between the spheres
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The Solar System
Formation of the Solar System
Formed 4.5 to 5 billion years ago
8 planets revolve around the Sun
4 terrestrial planets
4 gas giants
Earth is the third planet
Figure 1-4
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The Solar System
Figure 1-5
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9. The Size and Shape of the Earth
Earth’s Physical Characteristics
Equatorial diameter ~ 12,756 km
Polar diameter ~ 12,714 km
Circumference of 40,000 km
Maximum relief
Figure 1-6
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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 and perpendicular to Earth’s surface
graticule
Figure 1-9
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The Geographic Grid
Great Circles
Circles which bisect a sphere and pass through the sphere’s center
Identify the shortest distance between two points on a sphere—great circle distance
Circle of illumination
Small circles
Figure 1-10
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The Geographic Grid
Latitudes
Parallels
angle north or south of the equator
7 important latitudes:
Tropic of Cancer and Capricorn
(23.5° N and S)
Equator (0°)
Poles (90° N and S)
Arctic and Antarctic Circles
(66.5° N and S)
Latitude zones
Figure 1-12
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The Geographic Grid
Longitudes
Meridians
Prime Meridian (0° longitude) located at Greenwich, England
angle east or west of the Prime Meridian
Converge at the poles
Figure 1-16
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Earth-Sun Relations
Rotation of the Earth
24 hours for one rotation
Circular motion at all latitudes but the poles
Rotation is counterclockwise relative to the North Pole
Converge at the poles
Diurnal transition from light to darkness
Tidal effects from the Moon and Sun
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Earth-Sun Relations
Earth’s Revolution around Sun
One revolution takes 365 ¼ days
Elliptical orbit
Aphelion (152,171,500 km)
Perihelion (147,166,480 km)
Average distance (149,597,892 km)
Earth at perihelion during Northern Hemisphere winter; aphelion during Northern Hemisphere summer
Figure 1-19
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Earth-Sun Relations
Orbital Properties
Plane of the Earth’s orbit is the plane of the ecliptic
Earth’s axis tilted at 23.5°
Plane of ecliptic is not parallel to equatorial plane
Polarity of the Earth’s axis
Parallelism
North Pole always points toward Polaris (“North Star”)
Figure 1-20
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17. 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
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18. The Annual March of the Seasons
June solstice
Occurs on approximately June 22 each year
Sun is directly overhead at 23.5° N latitude
Antarctic Circle in 24 hours of darkness
Marks start of summer in Northern Hemisphere; winter in Southern Hemisphere
Figure 1-22
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19. The Annual March of the Seasons
December solstice
Occurs on approximately December 22 each year
Sun is directly overhead at 23.5° S latitude
Arctic Circle in 24 hours of darkness
Marks start of winter in Northern Hemisphere; summer in Southern Hemisphere
Figure 1-22
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20. The Annual March of the Seasons
Equinoxes
Occur on approximately March 21 and September 21 each year
Day length is 12 hours worldwide (“equinox”)
Sun is directly overhead at the equator
Figure 1-22
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21. 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
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22. The Annual March of the Seasons
Significance of seasonal patterns
Spread of solar rays over small and large areas
Tropical latitudes consistently warmer
Polar latitudes consistently cooler
Large seasonal variations in temperature in midlatitudes
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Telling Time
Three 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
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Telling Time
Current time system
24 time zones
Greenwich Mean Time (GMT) is standard
Controlling Meridian for each time zone
Several countries have multiple time zones in their borders
Time zone boundaries subject to local political and economic boundaries of different nations
180° meridian chosen as the International Date Line
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Telling Time
Time zones of the world
Figure 1-24
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Telling Time
Time zones of the United States
Figure 1-25
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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
Used
No longer used
Never been used
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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
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Summary
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
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Summary
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
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