Physical Geography: A Self-Teaching Guide

Physical Geography: A Self-Teaching Guide

by Michael Craghan
     
 

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Learn physical geography at your own pace

What is atmospheric pressure? How does latitude indicate the type of climate a specific place will have? Where are volcanic eruptions or strong earthquakes most likely to occur? With Physical Geography: A Self-Teaching Guide, you’ll discover the answers to these questions and many more about the basics of how

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Overview

Learn physical geography at your own pace

What is atmospheric pressure? How does latitude indicate the type of climate a specific place will have? Where are volcanic eruptions or strong earthquakes most likely to occur? With Physical Geography: A Self-Teaching Guide, you’ll discover the answers to these questions and many more about the basics of how our planet operates.

Veteran geography teacher Michael Craghan takes you on a guided tour of Earth’s surface, explaining our planet’s systems and cycles and their complex interactions step by step. From seasonal changes to coastal processes, from effluvial basins to deep sea fissures, Craghan puts the emphasis on comprehension of the topics. He also includes more than 100 specially commissioned illustrations and 50 photographs to help clarify difficult concepts. The clearly structured format of Physical Geography makes it fully accessible, providing an easily understood, comprehensive overview for everyone from the student to the amateur geographer to the hobbyist.

Like all Self-Teaching Guides, Physical Geography allows you to build gradually on what you have learned–at your own pace. Questions and self-tests reinforce the information in each chapter and allow you to skip ahead or focus on specific areas of concern. Packed with useful, up-to-date information, this clear, concise volume is a valuable learning tool and reference source for anyone who wants to improve his or her understanding of physical geography.

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Product Details

ISBN-13:
9780471445661
Publisher:
Wiley
Publication date:
09/19/2003
Series:
Wiley Self-Teaching Guides Series, #184
Pages:
292
Sales rank:
858,052
Product dimensions:
6.26(w) x 10.28(h) x 0.62(d)

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Physical Geography



A Self-Teaching Guide


By Michael Craghan


John Wiley & Sons



Copyright © 2003

Michael Craghan
All right reserved.



ISBN: 0-471-44566-5



Chapter One


Earth and Sun


Objectives

In this chapter you will learn that:

Earth is approximately 25,000 miles around.

Earth rotates on its axis, which generates night and day.

Latitude is an angle measurement used to identify a location on the
surface of Earth.

It takes Earth one year to revolve around the Sun.

Seasons are caused by how the tilt of Earth's axis affects the orientation
of the planet as it revolves around the Sun.

Hours of daylight are determined by Earth's orientation with the Sun.
Size and Shape of Earth

Size and Shape of Earth

Earth is a planet-it is a large body that moves around the Sun. It is not
a perfect sphere, but Earth is a spherically shaped object. Earth has these
approximate dimensions:

Radius: 4,000 miles (6,400 km)

Diameter: 8,000 miles (12,800 km)

Circumference: 25,000 miles (40,000 km)

These values can vary slightly due to differences in surface topography
and because Earth is not an exact sphere. If you could drive nonstop
around the equator at 60 mph it would take seventeen days to make
the trip.

What is the approximate distance around Earth (its circumference)?_____________

Answer: 25,000 miles (40,000 km)


Rotation, Poles, Equator

One feature of this planet is its rotation-it spins. It takes one day for
Earth to rotate on its axis (one day exactly, because that is the definition
of a day: one spin on its axis). Spinning leads to a reference system based
on the axis of rotation. The North and South Poles are at the ends of
the axis of rotation and thus can be used as unique reference points. If
Earth did not spin (and thus had no rotation axis), then any place would
be as good as any other for describing location.

Rotation also produces another feature of interest: the equator.
The equator is in a plane perpendicular to the axis of rotation, and it
divides the spherical Earth into halves. All of the points on one side
of the equator are closer to the North Pole than to the South Pole. All
of the points on the other side are closer to the South Pole. The half of
Earth closest to the North Pole is called the Northern Hemisphere
(half a sphere). The half of Earth closest to the South Pole is the Southern
Hemisphere.


What is the line that divides Earth into a half that is closer to the North
Pole and another half that is closer to the South Pole?_____________


Answer: the equator


Latitude

Once the two poles and the equator have been identified, then a system
of measurement called latitude can be established. Latitude is an angle
measurement from the equator to a point on Earth's surface. The angle
is measured from the center of Earth at the point where the rotation
axis intersects the plane of the equator.

The latitude system has some simple qualities:

All points on the equator are 0° away from the equator.

The North Pole is 90° away from the equator.

The South Pole is 90° away from the equator.

If the angle is measured toward the North Pole it is called north latitude.

If the angle is measured toward the South Pole it is called south latitude.

North and south are important! You must state whether a place has
north or south latitude to properly identify it.


What are the latitudes of points A, B, C, D, E, F, and G in Figure 1.5?
_____________

Answer: A=90°N, B=40°N, C=0°, D=30°S, E=90°S, F=60°S, G=23°30'N,

Revolution around the Sun

At the same time that it is rotating on its axis, Earth also is following a
path around the Sun. Earth is a planet that rotates on its axis and also
revolves around the Sun.

Rotate = axis = 1 day

Revolve = orbit = 1 year

It takes one year for Earth to revolve around the Sun (one year
exactly, because that is the definition of a year: one trip around the Sun).
This journey also takes 365 1/4 days (i.e., one year). So Earth will rotate
on its axis 365 1/4 times in the time it takes for the planet to go around the
Sun and return to its departing point.

The path that Earth travels along is an ellipse-but it is very close to
being a circle. The nearly circular path is used to define a geometric feature
called the plane of revolution. Although the planet orbits within the
plane of revolution-this is going to affect almost everything on Earth-Earth's
axis of rotation (the line running from the South Pole through
the North Pole) always points toward the North Star.

For the North Pole to be continuously directed toward the North
Star, Earth's axis has to be tilted 23 1/2° away from perpendicular to its
plane of revolution around the Sun. The direction and angle of the tilt
will always be the same: the axis is always aligned toward the North Star.
As a result of its constant aim to the North Star, the alignment of the
axis with the Sun is always changing. For part of its revolution around
the Sun, Earth's North Pole generally leans toward the Sun, and for the
other part of a year it leans away from the Sun.

In December, the North Pole leans away from the Sun.

In June, the North Pole leans toward the Sun.

In March and September, the line from Earth to the Sun is perpendicular
to the South Pole-North Pole axis.


Because the North Pole is always pointing to the North Star, Earth's
Northern Hemisphere is directed_____________the Sun in June and
_____________the Sun in December.

Answer: toward; away from

Tilt and Reference Latitudes

This tilt of Earth's axis creates five special latitude lines. These five lines
are the equator, two "tropics," and two "circles." Because tropics and
circles are lines of latitude, they are in planes that are perpendicular to
Earth's rotation axis and parallel to the plane of the equator.

Tropics are located at 23 1/2°N and 23 1/2°S, and just touch the plane of
revolution around the Sun. Circles are located at 66 1/2°N and 66 1/2°S
(23 1/2° + 66 1/2° = 90°), and they just touch the line that passes through
Earth's center and is perpendicular to the plane of revolution. The areas
bounded by these five latitude lines (equator, two tropics, and two
circles)react in different ways to the changing orientation of Earth and
the Sun over the course of a year.

66 1/2°N is the Arctic Circle. As Earth rotates on its axis, all of the
places on the North Pole side of this line will always be on the same
side of perpendicular as the North Pole.

23 1/2°N is the tropic of Cancer. As Earth rotates on its axis, all of the
places on the North Pole side of this line will always be above the
plane of revolution around the Sun. No point that is north of this line
will ever rotate to be directly on the plane of revolution.

The equator is at 0° latitude. As Earth rotates on its axis, all points at
the equator will spend half of each day above the plane of revolution
and half below it, and half of each day on the North Pole side of perpendicular
and half on the South Pole side.

23 1/2°S is the tropic of Capricorn. As Earth rotates on its axis, all
of the places on the South Pole side of this line will always be
below the plane of revolution around the Sun. No point that is
south of this line will ever rotate to be directly on the plane of revolution.

66 1/2°S is the Antarctic Circle. As Earth rotates on its axis, all of the
places on the South Pole side of this line will always be on the same
side of perpendicular as the South Pole.


Which two lines mark the farthest places north and south that can be
Directly on Earth's plane of revolution around the Sun?_____________

Answer: the tropic of Cancer (231/2°N) and the tropic of Capricorn (23 1/2°S)

Revolution, Alignment, and Day Length

As Earth travels around the Sun, Earth's tilt toward the North Star will
create four days when Earth-Sun alignment is in a special condition. In
June and December, there are solstices. A solstice is the moment when
the Sun is directly overhead at one of the tropics. This is the farthest
point north or south of the equator that the Sun can be directly overhead.
A solstice also is the day when a hemisphere is aimed either most
directly toward the Sun (summer solstice)or away from the Sun (winter
solstice).In September and March, there are equinoxes. An equinox
is the moment when the Sun is directly over the equator. Solstices and
equinoxes mark the extremes of orientation and a changeover with
respect to Sun conditions.


June Solstice

On the day of the June solstice, the North Pole is tilted as close as it gets
toward the Sun and the South Pole is tilted as far away as it gets. It is
summer in the Northern Hemisphere and winter in the Southern
Hemisphere. On this day:

The Sun will be directly overhead at 23 1/2°N (tropic of Cancer), and it
is strongest at that latitude.

All points in the Northern Hemisphere will get more than 12 hours
of sunlight; they spend more than half of the day rotating on the sunlit
side of the planet. All points in the Southern Hemisphere will get
fewer than 12 hours of sunlight.

All points on the equator will spend 12 hours rotating on the sunlit
side of Earth and 12 hours rotating on the dark side of Earth.

All points north of the Arctic Circle (66 1/2°N) will spend the entire
24-hour day rotating on the sunlit side of Earth.

All points south of the Antarctic Circle (66 1/2°S) will spend the entire
24-hour day rotating on the dark side of Earth.


September Equinox

On the day of the September equinox, the Sun is directly overhead at
the equator. It is the first day of autumn in the Northern Hemisphere
and the first day of spring in the Southern Hemisphere. On this day:

The Sun is most directly overhead at the equator.

All points on Earth will rotate on the sunlit side of the planet for 12
hours and rotate on the side away from the Sun for 12 hours.


December Solstice

On the day of the December solstice, the South Pole is tilted as close as
it gets toward the Sun and the North Pole is tilted as far away as it gets.
It is winter in the Northern Hemisphere and summer in the Southern
Hemisphere. On this day:

The Sun will be directly overhead at 23 1/2°S (tropic of Capricorn), and
it is strongest at that latitude.

All points in the Southern Hemisphere will get more than 12 hours
of sunlight; they spend more than half of the day rotating on the sunlit
side of the planet. All points in the Northern Hemisphere will get
fewer than 12 hours of sunlight.

All points on the equator will rotate 12 hours on the sunlit side of
Earth and rotate 12 hours on the dark side of Earth.

All points south of the Antarctic Circle (66 1/2°S) will spend the entire
24-hour day on the sunlit side of Earth.

All points north of the Arctic Circle (66 1/2°N) will spend the entire
24-hour day rotating on the dark side of Earth.

March Equinox

On the day of the March equinox, the Sun is directly overhead at the
equator. It is the first day of spring in the Northern Hemisphere and the
first day of autumn in the Southern Hemisphere. On this day:

The Sun is most directly overhead at the equator.

All points on Earth will be on the sunlit side of the planet for 12
hours and on the dark side for 12 hours.


"In-Between" Days

Because of the way Earth is tilted with respect to its plane of revolution,
the Sun can never be directly overhead north of 23 1/2°N (tropic
of Cancer)or south of 23 1/2°S (tropic of Capricorn).The Sun can only
be overhead in the tropics (between Cancer and Capricorn).The Sun
will be directly overhead at the equator on the two equinox days of
the year (in March and September).Days that are not an equinox or a
solstice (i.e., the other 361) are simply "in the middle." If you interpolate
between the solstice and equinox extremes, you should be able
to figure out Earth-Sun relations for any day. Here are the basic principles:

The Sun must be overhead somewhere between the tropics of Cancer
and Capricorn.

If it is March-September, the Sun will be directly overhead a place
in the Northern Hemisphere.

If it is September-March, the Sun will be directly overhead a place
in the Southern Hemisphere.

The closer a date is to a solstice, the closer to a tropic the Sun will
be overhead.

The closer a date is to an equinox, the closer to the equator the Sun
will be overhead.

Hours of daylight will be controlled by which hemisphere the Sun
is "in" (i.e., in which hemisphere it is overhead)and then by latitude.

In a hemisphere in which the Sun is overhead, the closer to a pole
a place is in that hemisphere, the more hours of daylight there
will be at that place.

There are 12 hours of daylight every day of the year at the equator.

In a hemisphere in which the Sun is not overhead, the closer to a
pole a place is in that hemisphere, the fewer hours of daylight
there will be at that place.


Why would a place like New York City (lat. 41°N) have about 15 hours of
daylight in June but only about 9 hours in December? __________

Answer: The Northern Hemisphere is tilted most directly toward the Sun in
June, and a place at 41°N spends most of a day on the illuminated part of
Earth. In December, the Northern Hemisphere is tilted away from the Sun,
and a place at 41°N spends most of a day on the dark side of Earth.

Seasonal Changes

Seasons are produced because Earth revolves around the Sun with a
tilted axis, which directs different parts of the planet toward or away
from the Sun at different stages of the journey.

Seasons have nothing to do with how close Earth and the Sun are to
each other. If proximity was the cause of seasons, then it would be the
same season in the Northern and Southern Hemispheres on the same day.

What causes seasons?_____________

Answer: The tilt of Earth's axis changes the alignments of the two hemispheres
and the Sun over the course of a year.

SELF-TEST

1. How much is Earth's rotation axis tilted away from perpendicular to
the planet's plane of revolution around the Sun?

a. 0° c. 78%°
b. 23%° d. 90°

2. The moment when the Sun is directly over either of the two tropics
is called a(n)

a. solstice c. season
b. equinox d. ellipse

3. The Sun is directly above the tropic of Cancer (23%°N) in which of
these months?

a. February c. June
b. April d. August

4. Earth's North Pole is always pointed toward the

5. The Sun is directly above the equator in the months of
and

6. The reason that it is hot in the summer is because that is when Earth
is closest to the Sun. (True or False)

7.

Continues...




Excerpted from Physical Geography
by Michael Craghan
Copyright © 2003 by Michael Craghan.
Excerpted by permission.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.

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