Chapter 1: Introduction to Earth
I.
II.
III.
IV.
V.
Geography as a Field of Learning
A. defining geography
1. “Earth description”
2. areal/spatial differentiation of elements on Earth’s surface
B. 2 branches of geography
1. Physical/environmental geography: elements that are natural in
origin
2. cultural/human geography: elements related to human endeavor
3. geography bridges the gap between physical and social sciences
C. “Why what is where and so what?
Science and Geography
A. The Process of Science
1. science is a process for gaining knowledge: observation;
experimentation; logical reasoning; skepticism of unsupported
conclusions; and, willingness to modify previous ideas
2. science does not prove ideas but rather works by eliminating
alternative explanations
3. theory: the highest order of understanding for a body of information in
science – a logical, well-tested explanation
B. Numbers and Measurement Systems
1. English system: used by USA
2. SI: International System of Units (metric): used by most of the world
and the entire scientific community
a. basic unit of length: meter
b. basic unit of mass (weight): gram
c. basic unit of volume: liter
d. basic unit of temperature: degrees Celsius
Global Environmental Change
A. some characteristics of the global environment are in state of perpetual
change
B. rate of change of atmosphere has generally been very slow but effects
have been profound
The Environmental Spheres
A. lithosphere: solid, inorganic portion of Earth
B. atmosphere: gaseous envelope of air that surrounds the Earth
C. hydrosphere: water in all its forms on Earth
1. cryosphere: subsphere of the hydrosphere that encompasses water
frozen as snow or ice
D. biosphere: all parts of the Earth where living organisms can exist
The Solar System
A. planets revolve counterclockwise around the sun in elliptical orbits
B. four inner terrestrial planets principally composed of mineral matter:
Mercury, Venus, Earth, Mars
Chapter 1: Introduction to Earth – p. 2 of 7
C. four outer Jovian planets mostly composed of gases: Jupiter, Saturn,
Uranus, Neptune
VI. The Size and Shape of the Earth
A. Earth’s dimensions:
1. Earth’s diameter ≈ 7,900 miles
2. distance from Sun: 93,000,000 miles
3. Earth’s maximum vertical relief ≈ 20 km/12 mi:
a. Mount Everest = 29,035 ft. above sea level
b. Mariana Trench (Pacific Ocean) = 36,198 ft. below sea level
B. The Shape of the Earth
1. Eratosthenes (200 BC) early calculations
2. oblate spheroid
a. rotation → equatorial bulge; flattening at poles
b. polar = 7,900 miles
c. equatorial = 7,927 miles
VII. The Geographic Grid
A. Intro
1. grid system: network of intersecting lines
2. reference features on Earth
a. rotation axis: imaginary line that connects the points on Earth’s
surface called the North Pole and the South Pole
b. equator
1) plane of the equator: imaginary plane passing through Earth
halfway between the poles and perpendicular to the axis of
rotation
2) equator: imaginary midline of Earth where the plane of the
equator intersects the Earth’s surface
3. Great Circles
a. great circle: line drawn on the surface of a sphere by a plane that
passes through the center of the sphere
1) the largest circle that can be drawn on a sphere; it divides the
sphere into 2 equal hemispheres
a) circle of illumination: edge of the sunlit hemisphere that is a
great circle separating Earth into a light half and a dark half
2) only one great circle can be constructed to include any 2 points
(unless diametrically opposed), and it’s always the shortest
distance between the points (great circle route)
b. small circle: line drawn on the surface of a sphere by a plane
passing through any part of the sphere other than the center
c. graticule: Earth’s geographic grid system, consisting of lines of
latitude and longitude
B. Latitude
1. latitude: location described as an angle measured north and south of
the equator
a. measured in degrees, minutes, and seconds
1) 360o in a circle
Chapter 1: Introduction to Earth – p. 3 of 7
2) 1o = 60’ (minutes)
3) 1’ = 60” (seconds)
b. range: 0o at equator  90o at either pole
1) any position north of the equator is north latitude
2) any position south of the equator is south latitude
2. parallel: line connecting all points of the same latitude
a. properties of parallels
1) the equator is the parallel at 0o latitude and is a great circle
2) all other parallels are small circles
3) parallels are true east-west lines
4) there are an infinite number
b. parallels of significance:
1) equator, 0o
2) Tropic of Cancer, 23.5oN
3) Tropic of Capricorn, 23.5oS
4) Arctic Circle, 66.5oN
5) Antarctic Circle, 66.5oS
6) North Pole, 90oN
7) South Pole, 90oS
3. Descriptive Zones of Latitude
a. Low latitude: equator (0o) → 30o N/S
b. Midlatitude: 30o N/S → 60o N/S
c. High latitude: 60o N/S → 90o N/S
d. Equatorial: within a few degrees of the equator
e. Tropical: within the tropics, 23.5o N → 23.5o S
f. Subtropical: ~25o-30o N/S
g. Polar: within a few degrees of the North or South Pole
4. Nautical Miles
a. each degree of latitude covers a north-south distance of ≈ 111
km/69 miles
b. nautical mile: distance covered by one minute (1’) of latitude; ≈
1.15 statue miles
c. knot: 1 nautical mile per hour
C. Longitude
1. longitude: location described as an angle measured east and west
from the prime meridian
2. meridian: imaginary line on earth’s surface extending from pole to pole
and crossing all parallels at right angles
a. properties of meridians
1) a meridian is a great semi-circle (half of a great circle that
extend from pole to pole)
2) meridians cross all parallels of latitude perpendicularly
3) meridians are true north-south lines
b. distance between meridians varies significantly, greatest at the
equator, diminishing to zero at the poles
Chapter 1: Introduction to Earth – p. 4 of 7
3. prime meridian: meridian passing through Greenwich, England, and
from which longitude is measured
4. range: from 0o at the prime meridian to 180o E or W (located in
middle of Pacific Ocean)
VIII. Earth-Sun Relations
A. Earth’s Rotation on its Axis
1. Earth rotates from west to east on its axis once every 24 hours;
looking down at North Pole from space, earth rotates in a
counterclockwise direction
2. speed of rotation on the Earth’s surface ranges from a maximum at the
equator to zero at the poles
3. effects on the physical characteristics of Earth’s surface:
a. Coriolis effect: apparent deflection of all fluids to the right in the
northern hemisphere and to the left in the southern hemisphere
(Chapter 3)
b. tides: effect on ocean water of the increasing and decreasing
gravitational pull of the moon and the sun (Chapter 9)
c. diurnal alternation of light and darkness influences local temperature,
humidity and wind movements
1) circadian (daily) rhythm: adaptation to sequential patterns of light
and darkness
2) jet lag: result of disruption of one’s circadian rhythm
B. Earth’s Revolution Around the Sun
1. tropical year: ~365.25 days
2. elliptical orbit
a. earth’s orbit around the sun is an ellipse, not a true circle
b. distance from sun varies throughout the year
1) perihelion: point in its orbit at which the Earth is closest to the sun
a) Jan 3
b) 91,455,000 miles
2) aphelion: point in its orbit at which Earth is farthest from the sun
a) July 4
b) 94,555,000 miles
3) Earth is 3.3% closer to the sun during northern hemisphere’s winter
c. one astronomical unit (1 AU): average Earth-sun distance;
92,955,806 miles
C. Inclination of Earth’s Axis
1. plane of the ecliptic: imaginary plane defined by the orbital path of
Earth around the sun
2. inclination of Earth’s axis: tilted 23.5o away from the perpendicular
D. Polarity of Earth’s Axis
1. polarity/parallelism: characteristic of Earth’s axis wherein it always
points toward Polaris (North Star) at every position in Earth’s orbit
around the sun
2. combined effect of rotation, revolution, inclination, and polarity
result in Earth’s seasonal patterns
Chapter 1: Introduction to Earth – p. 5 of 7
IX.
The Annual March of the Seasons
A. 3 conditions vary with latitude and affect solar radiation:
1. subpolar point/sun’s declination: the latitude receiving the vertical
rays of the sun
2. solar altitude: height of the sun above the horizon
3. length of the day
B. June Solstice
1. occurs on approximately June 21
2. Earth reaches position in its orbit where the North Pole is oriented
most directly toward the sun
3. noon rays of the sun are perpendicular at 23.5oN latitude/Tropic of
Cancer; the sun is directly overhead this parallel at noon
a. Tropic of Cancer marks the northernmost location where the sun
is ever directly overhead
4. circle of illumination: dividing line between the daylight half of the
Earth and the nighttime half of the earth
a. bisects the equator on June solstice (12 hours of daylight, 12 hours
of darkness at equator)
b. north of the equator day length increases, > 12 hours
c. south of the equator day length decreases, < 12 hours
d. all points north of 66.5oN receive 24 hours of daylight
1) Arctic Circle – special parallel defines the 24 hours of daylight
e. all points south of 66.5oS receive 24 hours of darkness
1) Antarctic Circle - special parallel defines 24 hours of darkness
5. June 21: summer solstice in northern hemisphere, winter solstice in
southern hemisphere
C. September Equinox
1. occurs on approximately September 22
2. characteristics:
a. the noon rays of the sun are perpendicular to the Earth’s surface at
the equator (0o); the sun is directly overhead the equator at noon
b. circle of illumination touches both poles
c. all locations on earth experience 12 hours of daylight and 12
hours of darkness
d. at the equator every day of the year has 12 hours of daylight and 12
hours of darkness; all other locations have equal day and night only
on an equinox
3. autumnal equinox in northern hemisphere; vernal equinox in
southern hemisphere
D. December Solstice
1. occurs on approximately December 21
2. Earth reaches position in its orbit where the North Pole is oriented
most directly away the sun
3. noon rays of the sun are perpendicular at 23.5oS latitude/Tropic of
Capricorn; the sun is directly overhead this parallel at noon
Chapter 1: Introduction to Earth – p. 6 of 7
a. Tropic of Capricorn marks the southernmost location where the
sun is ever directly overhead
4. all points north of 66.5oN (Arctic Circle) receive 24 hours of darkness
5. all points south of 66.5oS (Antarctic Circle) receive 24 hours of daylight
6. relationships between the earth and the sun are very similar on the June and
December solstices – the conditions in each hemisphere are simply reversed
7. December 21: winter solstice in northern hemisphere, summer solstice in
southern hemisphere
E. March Equinox
1. occurs on approximately March 20
2. the relationships of earth and the sun are virtually identical on the
March equinox and the September equinox
4. vernal equinox in northern hemisphere; autumnal equinox in
southern hemisphere
F. Seasonal Transitions
1. Latitude Receiving the Vertical Rays of the Sun
a. the vertical rays of the sun can only strike Earth between the Tropic
of Cancer and the Tropic of Capricorn
b. following March equinox, vertical rays of the sun migrate from equator
northward and strike the Tropic of Cancer (23.5oN) on the June solstice
1) latitudes north of the Tropic of Cancer never experience the
vertical rays of the sun
2) the June solstice marks the day of the year when the sun is highest
in the sky for all latitudes north of the Tropic of Cancer
c. after the June solstice the vertical rays migrate southward and
strike the equator again on the September equinox
d. vertical rays of the sun strike the Topic of Capricorn (23.5oS), their
southernmost latitude, on the December solstice
1) the December solstice marks the day of the year when the sun
in lowest in the sky in the northern hemisphere
e. after the December solstice the vertical rays migrate northward and
strike the equator again on the March equinox
2. Day Length
a. only at the equator is day length constant throughout the year = 12
hours of daylight every day
b. Dec solstice is the shortest day of the year in the northern
hemisphere
c. March and September equinox, day length is 12 hours
d. June solstice is the longest day of the year in the northern
hemisphere
3. Day Length in the Arctic and Antarctic
a. on the March equinox the sun rises at the North Pole and is above
the horizon continuously for the next 6 months
b. June solstice: the entire region from the North Pole to the Arctic
Circle experiences 24 hours of daylight
Chapter 1: Introduction to Earth – p. 7 of 7
X.
c. on the September equinox the sun sets on the North Pole and
remains below the horizon for the next 6 months
d. December solstice: the entire region from the North Pole to the
Arctic Circle experiences 24 hours of darkness
G. Significance of Seasonal Patterns
a. principal determinants of amount of solar energy received at any
particular latitude:
1) angle at which sun’s rays strike the earth: the higher the angle at
which sunlight strikes the earth, the more effective the resultant heating
2) day length: short periods of daylight in winter and long periods of
daylight in summer contribute to seasonal differences in
temperature in mid- and high latitudes
b. tropical latitudes – always warm
1) have high sun angles year-round and day lengths consistently
about 12 hours
c. polar regions – consistently cold
1) low sun angles year-round
d. midlatitudes: seasonal temperature differences are large because of
sizable seasonal variations in angles and day length
Telling Time
A. Standard Time
1. meridians and standard time
a. 1884 International Prime Meridian Conference
b. world divided into 24 standard time zones
c. each time zone extends over 15o of longitude
d. the Prime Meridian at Greenwich, England and all meridians that are
multiples of 15o east and west are centers of the 24 time zones
e. Greenwich mean time (GMT)/Universal Time Coordinated (UTC)
2. countries and time zones
a. US covers 6 time zones
b. time zone boundaries vary over land to coincide with political and economic
boundaries
c. Russia covers 9 time zones; China covers 4 but entire country on
Beijing time
B. The International Date Line
1. located at 180oE and W; the 180o meridian of longitude
2. opposite arc of the prime meridian
3. passes through center of Pacific Ocean
4. crossing the international date line from west to east gains a day; from
east to west loses a day
C. Daylight Savings Time
1. energy conservation measure
2. in U.S. move clock ahead an hour in March; set clock back an hour in
November
3. Arizona, Hawaii and part of Indiana do not observe daylight savings time