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PART ONE:
The Energy-Atmosphere System
Geosystems begins with the Sun and Solar System to launch the first of four parts. Our planet and our lives are
powered by radiant energy from the star closest to Earth—the Sun. Each of us depends on many systems that
are set into motion by energy from the Sun. These systems are the subjects of Part One.
Part One exemplifies the systems organization of the text: it begins with the origin of the solar system and
the Sun. Solar energy passes across space to Earth’s atmosphere varying seasonally in its effects on the
atmosphere (Chapter 2). Insolation then passes through the atmosphere to Earth’s surface (Chapter 3). From
Earth’s surface, and surface energy balances (Chapter 4) generate patterns of world temperature (Chapter 5) and
general and local atmospheric circulation (Chapter 6). Each of the text’s four parts contains related chapters
with content arranged according to the flow of individual systems or in a manner consistent with time and the
flow of events.
The Part-opening photo shows The Midnight Sun seen from a research ship in the Arctic Ocean. The
camera points due north, viewing the Sun’s rays from across the North Pole some 885 km (550 mi) distant (see
the inset illustration). The author commented that it seemed strange at the time to have natural lighting that felt
like about 3 P.M. (15:00 hours), yet his watch clearly showed it to be midnight. See Figure 2.16 for a nearmidnight Antarctic scene.
Solar Energy to Earth
and the Seasons
2
Overview
The ultimate spatial inquiry is to know the location of
Earth in the Universe. To properly set the stage for a
course in the physical geography of Earth, slides,
videography, Internet sites, and posters can be used
to establish the location and place of our planetary
home. Our immediate home is North America, a
major continent on planet Earth, the third planet from
a typical yellow star in a solar system. That star, our
Sun, is only one of billions in the Milky Way Galaxy,
which is one of billions of galaxies in the Universe.
This chapter examines the nature of the flow of
energy and material from the Sun to the outer reaches
of Earth’s atmosphere. The top of the atmosphere is a
measuring point to assess the arriving solar energy.
Earth receives solar wind and electromagnetic
radiation from the Sun.
Earth’s orientation to the Sun varies seasonally.
The chapter ends with a discussion of seasons and
seasonal changes in insolation and daylength.
As before, a list of key learning concepts begins
the chapter and is used to organize the Summary and
Review section, with definitions, key terms and page
numbers, and review questions grouped under each
objective. At the beginning of each chapter a section
titled “In This Chapter” introduces the chapter’s
content in a succinct statement.
Outline Headings and Key Terms
The first-, second-, and third-order headings that
divide Chapter 2 serve as an outline. The key terms
and concepts that appear boldface in the text are
listed here under their appropriate heading in bold
italics. All these highlighted terms appear in the text
glossary. Note the check-off box () so you can
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mark class progress. The students have this same list
in their Student Study Guide. The  icon indicates
that there is accompanying material on the Student
CD.
The outline headings and terms for Chapter 2:
Milky Way Galaxy
The Solar System, Sun, and Earth
 Nebular Hypothesis
Solar System Formation and
Structure
gravity
planetesimal hypothesis
Dimensions and Distances
speed of light
Earth’s Orbit
perihelion
aphelion
plane of the ecliptic
Solar Energy: From Sun to Earth
Electromagnetic Spectrum and Plants
fusion
Solar Activity and Solar Wind
solar wind
sunspots
Solar Wind Effects
magnetosphere
auroras
Weather Effects
Electromagnetic Spectrum of
Radiant Energy
electromagnetic
spectrum
wavelength
Incoming Energy at the Top
of the Atmosphere
thermopause
insolation
Solar Constant
solar constant
Uneven Distribution of Insolation
subsolar point
Global Net Radiation
The Seasons
 Earth-Sun Relations, Seasons
Seasonality
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altitude
declination
daylength
Reasons for Seasons
Revolution
revolution
Rotation
rotation
axis
circle of illumination
Tilt of Earth’s Axis
axial tilt
Axial Parallelism
axial parallelism
Sphericity
Annual March of the Seasons
sunrise
sunset
winter solstice
December solstice
vernal equinox
March equinox
summer solstice
June solstice
autumnal equinox
September equinox
Dawn and Twilight
Seasonal Observations
SUMMARY AND REVIEW
News Reports
News Report 2.1: The Nature of Order Is Chaos
News Report 2.2: Monitoring Earth Radiation Budget
URLs listed in Chapter 2
Solar systems simulator:
http://space.jpl.nasa.gov/
Sunspot cycle and auroral activity:
http://solarscience.msfc.nasa.gov/SunspotCycle.shtml
http://www.spaceweather.com/
http://www.sel.noaa.gov/pmap/
http://www.gi.alaska.edu
http://northernlightsnome.homestead.com/
International Earth Rotation Service:
http://www.iers.org/
Sunrise, sunset calculator:
http://www.srrb.noaa.gov/highlights/sunrise/
sunrise.html
URLs of Interest
Hubble telescope and astronomy info:
http://sohowww.nascom.nasa.gov/gallery/
http://www.seds.org/hst/
the naked eye can see only a few thousand of the
nearly 400 billion stars.
Key Learning Concepts for Chapter 2
The following learning concepts help guide the
student’s reading and comprehension efforts. The
operative word is in italics. These are included in
each chapter of Geosystems and the Geosystems
Student Study Guide. The student is told: “after
reading the chapter you should be able to”:
• Distinguish among galaxies, stars, and planets,
and locate Earth.
• Overview the origin, formation, and
development of Earth and the atmosphere and
construct Earth’s annual orbit about the Sun.
• Describe the Sun’s operation, and explain the
characteristics of the solar wind and the
electromagnetic spectrum of radiant energy.
• Portray the intercepted solar energy and its
uneven distribution at the top of the
atmosphere.
• Define solar altitude, solar declination, and
daylength; describe the annual variability of
each—Earth’s seasonality.
3. Briefly describe Earth’s origin as part of the
Solar System.
According to prevailing theory, our Solar System
condensed from a large, slowly rotating, collapsing
cloud of dust and gas called a nebula. As the nebular
cloud organized and flattened into a disk shape, the
early proto-Sun grew in mass at the center, drawing
more matter to it. Small accretion (growing) eddies—
the protoplanets—swirled at varying distances from
the center of the solar nebula. The early protoplanets,
or planetesimals, were located at approximately the
same distances from the Sun that the planets are
today. The beginnings of the Sun and the solar
system are estimated to have occurred more than 4.6
billion years ago. These processes are now observed
as occurring elsewhere in the galaxy. Astronomers so
far have observed almost two dozen stars with
planets orbiting about them.
4. Compare the locations of the nine planets of the
Solar System.
See Figure 2.1c and d for this information. There
is
a
Solar
System
simulation
at
http://space.jpl.nasa.gov/.
Annotated Chapter Review Questions
• Distinguish among galaxies, stars, and planets,
and locate Earth.
1. Describe the Sun’s status among stars in the
Milky Way Galaxy. Describe the Sun’s location,
size, and relationship to its planets.
Our Sun is both unique to us and commonplace
in our galaxy. It is only average in temperature, size,
and color when compared with other stars, yet it is
the ultimate energy source for almost all life
processes in our biosphere. Planets do not produce
their own energy. Our Sun is located on a remote,
trailing edge of the Milky Way Galaxy, a flattened,
disk-shaped mass estimated to contain up to 400
billion stars.
2. If you have seen the Milky Way at night, briefly
describe it. Use specifics from the text in your
description.
From our Earth-bound perspective in the Milky
Way, the galaxy appears to stretch across the night
sky like a narrow band of hazy light. On a clear night
• Overview the origin, formation, and development
of Earth and the atmosphere and construct
Earth’s annual orbit about the Sun.
5. How far is Earth from the Sun in terms of light
speed? In terms of kilometers and miles?
Earth’s orbit around the Sun is presently
elliptical—a closed, oval-shaped path (Figure 2.1d).
Earth’s average distance from the Sun is
approximately 150 million km (93 million mi).
Divided by the speed of light, this places us 8
minutes and 20 seconds from the Sun. In other words
it takes light that time to travel across planetary space
to Earth.
6. Briefly describe the relationship among these
concepts: Universe, Milky Way Galaxy, Solar
System, Sun, and Planet Earth.
The Universe is infinite in size and dimension
from our perspective. Tens of billions of galaxies are
known to populate the Universe we can observe, each
composed of hundreds of billions of stars. Our Sun is
a typical yellow-dwarf thermonuclear (fusion) star,
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somewhat less than a million miles in diameter.
Planets orbit about stars such as our Solar System.
Our Sun and the orbiting planets are revolving
around the Milky Way Galaxy in a vast clockwise
spiral.
Similar multiple-planet solar systems are now
being studied through the Hubble and other
telescopes. More than 60 planets outside our Solar
Systems are now identified and planets forming in a
manner similar to how scientists think Earth formed
are being observed. The astronaut-delivered upgrade
on the Hubble that took place in 2002 has produced
astounding results since the already prodigious power
was increased a full ten times and the thermal
infrared telescope was restored.
7. Diagram in a simple sketch Earth’s orbit about
the Sun. How much does it vary during the course
of a year?
Earth is at perihelion (its closest position to the
Sun) during the Northern Hemisphere winter
( January 3 at 147, 255, 000 km, or 91,500,000
mi). It is at aphelion (its farthest position from the
Sun) during the Northern Hemisphere summer ( July
4 at 152,083,000 km, or 94,500,000 mi). This
seasonal difference in distance from the Sun causes a
slight variation in the solar energy intercepted by
Earth, but is not an immediate reason for seasonal
change.
• Describe the Sun’s operation and explain the
characteristics of the solar wind and the
electromagnetic spectrum of radiant energy.
8. How does the Sun produce such tremendous
quantities of energy?
The solar mass produces tremendous pressure
and high temperatures deep in its dense interior
region. Under these conditions, pairs of hydrogen
nuclei, the lightest of all the natural elements, are
forced to fuse together. This process of forcibly
joining positively charged nuclei is called fusion. In
the fusion reaction hydrogen nuclei form helium, the
second lightest element in nature, and liberate
enormous quantities of energy in the form of free
protons, neutrons, and electrons. During each second
of operation, the Sun consumes 657 million tons of
hydrogen, converting it into 652.5 million tons of
helium. The difference of 4.5 million tons is the
quantity that is converted directly to energy—
resulting in literally disappearing solar mass.
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9. What is the sunspot cycle? At what stage was
the cycle in 2001?
A regular cycle exists for sunspot occurrences,
averaging 11 years from maximum peak to maximum
peak; however, the cycle may vary from 7 to 17
years. In recent cycles, a solar minimum occurred in
1976, whereas a solar maximum took place in 1979,
when over 100 sunspots were visible. Another
minimum was reached in 1986, and an extremely
active solar maximum occurred in 1990 with over
200 sunspots, 11 years from the previous maximum,
in keeping with the average. In 1997, we witnessed a
solar minimum. In 2001, the cycle returned to an
intense maximum, causing auroras to be visible at
lower latitudes. The minimum may have been
reached in 2007, with cycle 24 beginning in 2008 and
forecast to reach a maximum in 2012.
10. Describe Earth’s magnetosphere and its effects
on the solar wind and the electromagnetic
spectrum.
Earth’s outer defense against the solar wind is
the magnetosphere, which is a magnetic force field
surrounding Earth, generated by dynamo-like
motions within our planet. As the solar wind
approaches Earth, the streams of charged particles are
deflected by the magnetosphere and course along the
magnetic field lines. The extreme northern and
southern polar regions of the upper atmosphere are
the points of entry for the solar wind stream.
11. Summarize the presently known effects of the
solar wind relative to Earth’s environment.
The interaction of the solar wind and the upper
layers of Earth’s atmosphere produces some
remarkable phenomena relevant to physical
geography: the auroras, disruption of certain radio
broadcasts and even some satellite transmissions, and
possible effects on weather patterns.
12. Describe the segments of the electromagnetic
spectrum, from shortest to longest wavelength.
What wavelengths are mainly produced by the
Sun? Which are principally radiated by Earth to
space?
See Figures 2.6 and 2.7. All the radiant energy
produced by the Sun is in the form of electromagnetic
energy and, when placed in an ordered range, forms
part of the electromagnetic spectrum. The Sun emits
radiant energy composed of 8% ultraviolet, X-ray,
and gamma ray wavelengths; 47% visible light
wavelengths; and 45% infrared wavelengths.
Wavelengths emitted from the Earth back to the Sun
are of lower intensity and composed mostly of
infrared wavelengths.
• Portray the intercepted solar energy and its
uneven distribution at the top of the
atmosphere.
13. What is the solar constant? Why is it
important to know?
The average value of insolation received at the
thermopause (on a plane surface perpendicular to the
Sun’s rays) when Earth is at its average distance from
the Sun. That value of the solar constant is 1372
watts per square meter (W/m2). A watt is equal to one
joule (a unit of energy) per second and is the standard
unit of power in the SI-metric system. (See Appendix
C in Geosystems for more information on
measurement conversions.) In nonmetric calorie heat
units, the solar constant is expressed as
approximately 2 calories (1.968) per cm2 per minute,
or 2 langleys per minute (a langley being 1 cal per
cm2). A calorie is the amount of energy required to
raise the temperature of one gram of water (at 15° C)
one degree Celsius and is equal to 4.184 joules.
Knowing the amount of insolation intercepted by
Earth is important to climatologists and other
scientists as a basis for atmospheric and surface
energy measurements and calculations.
14. Select 40° or 50° north latitude on Figure 2.10,
and plot the amount of energy in W/m2 per day
characteristic of each month throughout the year.
Compare this to the North Pole; to the equator.
See Figure 2.10. Note the watts per m2 received
at each month for specific latitudes. Graphs at key
latitudes are placed along the right-hand side of the
chart.
15. If Earth were flat and oriented perpendicular
to incoming solar radiation (insolation), what
would be the latitudinal distribution of solar
energy at the top of the atmosphere?
The atmosphere is like a giant heat engine driven
by differences in insolation from place to place (see
Figure 2.9). If Earth were flat there would be an even
distribution of energy by latitude with no differences
from place to place and therefore little motion
produced.
• Define solar altitude, solar declination, and
daylength and describe the annual variability of
each—Earth’s seasonality.
16. Assess the 12-month Gregorian calendar, with
its months of different lengths, and leap years, and
its relation to the annual seasonal rhythms—the
march of the seasons. What do you find?
The Gregorian calendar in common use has no
relation to natural rhythms of Sun, Earth, the Moon,
and the march of the seasons.
17. The concept of seasonality refers to what
specific phenomena? How do these two aspects of
seasonality change during the year at 0° latitude?
At 40°? At 90°?
Seasonality refers to both the seasonal variation
of the Sun’s rays above the horizon and changing
daylengths during the year. Seasonal variations are a
response to the change in the Sun’s altitude, or the
angular difference between the horizon and the Sun.
Seasonality also means a changing duration of
exposure, or daylength, which varies during the year
depending on latitude. People living at the equator
always receive equal hours of day and night, whereas
people living along 40° N or S latitude experience
about six hours’ of difference in daylight hours
between winter and summer; those at 50° N or S
latitude experience almost eight hours of annual
daylength variation. At the polar extremes the range
extends from a six-month period of no insolation to a
six-month period of continuous 24-hour days.
18. Differentiate between the Sun’s altitude and its
declination at Earth’s surface.
The Sun’s altitude is the angular difference
between the horizon and the Sun. The Sun is directly
overhead at zenith only at the subsolar point. The
Sun’s declination—that is, the angular distance from
the equator to the place where direct overhead
insolation is received—annually migrates through 47
degrees of latitude between the two tropics at 23.5° N
and 23.5° S latitudes.
19. For the latitude at which you live, how does
daylength vary during the year? How does the
Sun’s altitude vary? Does your local newspaper
publish a weather calendar containing such
information?
See reference materials in this resource manual
chapter to guide the students. See Table 2.3. See the
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sunrise/sunset calculator at
htttp://www.srrb.noaa.gov/highlights/sunrise/
sunrise.html
20. List the five physical factors that operate
together to produce seasons.
Table 2.1 details these five factors: Earth’s
revolution and rotation, its tilt and fixed-axis
orientation, and its sphericity.
21. Describe revolution and rotation, and
differentiate between them.
The structure of Earth’s orbit and revolution
about the Sun is described in Figures 2.1, 2.13, and
2.14. Earth’s revolution determines the length of the
year and the seasons. Earth’s rotation, or turning, is a
complex motion that averages 24 hours in duration.
Rotation determines daylength, produces the apparent
deflection of winds and ocean currents, and produces
the twice daily action of the tides in relation to the
gravitational pull of the Sun and the Moon. Earth’s
axis is an imaginary line extending through the planet
from the North to South geographic poles.
22. Define Earth’s present tilt relative to its orbit
about the Sun.
Think of Earth’s elliptical orbit about the Sun as
a level plane, with half of the Sun and Earth above
the plane and half below. This level surface is termed
the plane of the ecliptic. Earth’s axis is tilted 23.5°
from a perpendicular to this plane.
23. Describe seasonal conditions at each of the
four key seasonal anniversary dates during the
year. What are the solstices and equinoxes and
what is the Sun’s declination at these times?
See Tables 2.3, 2.4, and Figures 2.15 and 2.18,
and the seasonal changes monitored from orbit in
Figure 2.19.
Overhead Transparencies for Chapter 2
As an adopter you are provided with the following figures for overhead projector use.
T-No.
Geosystems 7/E figure
Figure description from Geosystems 7/E
number and page
15.
2.1 (p. 43)
Milky Way Galaxy, Solar System, and Earth’s orbit
16.
2.6 (p. 47)
The electromagnetic spectrum of radiant energy
17.
2.7 (p. 47)
Solar and terrestrial energy distribution by wavelength
18.
2.8 & 2.9 (p. 48)
Earth’s energy budget simplified; Insolation receipts and Earth’s curved
surface
19.
2.13 & 2.14 (pp. 52, 53)
Earth’s revolution and rotation; The plane of the Earth’s orbit (the plane
of the ecliptic)
20.
2.15 (p. 54)
Annual march of the seasons
21.
2.18 (p. 56)
Seasonal observations—sunrise, noon, sunset at 40° N latitude
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