Visualizing Physical Geography
by Alan Strahler and Zeeya Merali
Chapter 1
The Earth as a Rotating Planet
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Chapter Overview—Also
Visual summary
The Shape of the Earth
The Earth’s Rotation
The Geographic Grid
Map Projections
Global Time
The Earth’s Revolution Around the Sun
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Key Chapter Objectives
Define the axis and poles.
Examine the method we use to
determine position on the globe.
Explain map projections and their
differences.
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Key Chapter Objectives
Describe how the sun’s position
regulates time, the need for world time
zones and the use of daylight savings
time.
Explain and illustrate how the seasons
are created, focusing on seasonal
variation.
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
The Shape of the Earth
The Earth is round
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
The Shape of the Earth
The Earth is not a perfect sphere
• Equatorial diameter slightly greater than polar diameter
• Earth is an oblate ellipsoid–slightly flattened
• The geoid exaggerates small departures from spherical
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
The Earth’s Rotation
Earth rotates on its axis:
•Counterclockwise at North Pole
•Left to right (eastward) at Equator
Axis: an imaginary
straight line through the
center of the Earth
around which the Earth
rotates
•One rotation is a solar day (24 hours)
Poles: the two points on
the Earth’s surface
where the axis of
rotation emerges
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
The Earth’s Rotation
Environmental Effects of the Earth’s Rotation:
•Day and night
•Fluctuating air temperature
•Coriolis Effect
•Tides
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
The Geographic Grid
Parallels and Meridians
Geographic grid: network of parallels and meridians used to fix location
on the Earth
Parallel: east-west circle on
the Earth’s surface, lying on a
plane parallel to the equator
Meridian: north-south line on the
Earth’s surface, connecting the
poles
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
The Geographic Grid
Parallels and Meridians
Equator: Parallel of latitude lying midway between the Earth’s poles; it is
designated latitude 0º
• Longest parallel of latitude
• Midway between poles
• Fundamental reference line for measuring position
Latitude: arc of a
meridian between
the equator and a
given point on the
globe
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Longitude: arc of a
parallel between
the prime meridian
and a given point
on the globe
The Geographic Grid
Latitude and Longitude
Latitude is measured north and
south of the equator, up to 90º
Longitude is measured east and
west of the Prime Meridian—
meridian that passes through
Greenwich, England—up to 180º
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Map Projections
Many types of maps, for many different purposes
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Map Projections
1:50,000
Map Scale
Scale fraction: a ratio
that tells how to convert
distance on the map to
true distance on the
Earth
1 unit of map
distance=50,000 units
of distance on the
Earth
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Map Projections
Map projection: a system of parallels and meridians
representing the Earth’s curved surface drawn on a flat surface
• Curved surface cannot be projected onto a flat sheet without distortion
• Each map projection has a specific purpose
• Each projection has advantages and drawbacks
View map projections in
Student resources Wiley Plus
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Map Projections
Mercator projection: map projection with horizontal parallels and
vertical meridians
• Used for navigation-sailors
• Scale increases from equator to poles for parallels—spaces differs- higher latitude
(above 60 degrees is double than at the equator. Needs to be cut off at 80 and
enlarges features at the poles.
• Straight line features- Use maps of temperatures, winds, and pressures
• Straight line on a Mercator projection not the shortest distance between two points
Map Projections
Goode Projection: Equal-area map projection often used
to display information such as climate or soil type
• Shows true sizes of regions on Earth’s surface
• Distorts shapes of places, especially high latitudes and at edges of map
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Map Projections
Polar projection: map projection centered on Earth’s North or
South Pole
• Used for maps of polar regions
• Scale increases outward
• Shows only one hemisphere
•Use in weather maps
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Global Time
Standard Time: time system based on the local time of a
standard meridian and applied to belts of longitude extending
roughly 7 ½ º on either side of the meridian
Time zones: zones
or belts within which
standard time is
applied
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Global Time
World Time Zones
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Global Time
International Date Line
•180th meridian
•Moving west across the date line: advance calendar one day
•Moving east across date line: set calendar back one day
•No change in clock time when crossing date line
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Global Time
Daylight Saving Time: clocks set ahead one hour
Not observed in all locations
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Earth’s Revolution Around the Sun
Earth revolves around the sun every 365.242 days
• Orbit is an ellipse
• Leap year corrects for the extra quarter day
• Orbit is counterclockwise
• Perihelion: point in orbit when Earth is closest to Sun
• Aphelion: point in orbit when Earth is farthest from Sun
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Earth’s Revolution Around the Sun
Tilt of the Earth’s Axis
Earth has seasons because of the tilt of the axis.
• Axis aims toward Polaris
(North Star)
Plane of the Ecliptic: plane of the
Earth’s orbit around the Sun
• Axis tilted at an angle of
23 ½ ° from a right angle to
plane of the ecliptic
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Earth’s Revolution Around the Sun
The Four Seasons View Angle of Sun in the Sky in Wiley Plus
Earth’s axis tilted toward North Star throughout Earth’s orbit.
• December 22: N hemisphere tilted away from the sun at the maximum angle
• June 21: N hemisphere tilted toward the sun at the maximum angle
•Subsolar point- Single point on earth’s surface sun directly overhead.
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Earth’s Revolution Around the Sun
The Four Seasons
Circle of illumination: separates day
hemisphere from night hemisphere
Summer solstice:
solstice occurring on
June 21 or 22, when
the subsolar point is
at 23 1/2° N; June
Solstice
Equinox: time when
subsolar point falls on
equator and circle of
illumination passes through
both poles
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Winter solstice:
solstice occurring on
December 21 or 22,
when the subsolar
point is at 23 1/2° S;
December Solstice
Earth’s Revolution Around the Sun
Equinox Conditions
• Circle of illumination
passes through both
poles
• Subsolar point at
equator
• Day and night of equal
length everywhere on
the globe
•Occurs twice per year
•Vernal Equinox:
March 21
•Autumnal Equinox:
September 23
Subsolar point: point on the Earth’s surface
where the sun is directly overhead at noon
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Earth’s Revolution Around the Sun
Solstice Conditions
• Circle of illumination grazes Arctic and Antarctic Circles
• June Solstice: north pole has 24 hours of daylight; daylength increases from equator to
north pole
• December Solstice: south pole has 24 hours of daylight; daylength increases from
equator to south pole
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Discussion
Pair/Share
Answer the following questions yourself. Pair
up and discuss. Share with class.
How have ecosystems in your city been
affected by human activity? Good or bad.
How have various kinds of pollution affected
your life? List some sources of pollution in
your city.
What do you consider the most important
pollution threat to the Earth.
What are 3 things people could do to improve
the quality of earth systems.