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

2. 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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4. 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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5. 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
1. atmosphere—“air”
2. lithosphere—“stone”
3. hydrosphere—“water”
4. biosphere—“life”
6
2 3
1
4
Interactions between the spheres
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7. 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
7
Figure 1-4
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8. The Solar System
8
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
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Figure 1-6

10. 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
10
Figure 1-9
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11. 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
11
Figure 1-10
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12. 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
12
Figure 1-12
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13. 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
13
Figure 1-16
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14. 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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15. 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
15
Figure 1-19
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16. 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”)
16
Figure 1-20
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17. The Annual March of the Seasons
17
• 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
18
• 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
19
• 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
20
• 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
21
• 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
22
• 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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23. Telling Time
23
• 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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24. Telling Time
24
• 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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25. Telling Time
25
Figure 1-24
• Time zones of the world
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26. Telling Time
26
• Time zones of the United States
Figure 1-25
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27. Telling Time
27
• 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
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28. Summary
28
• 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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29. Summary
29
• 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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30. Summary
30
• 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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