Physical
geography centers on spatial analysis of all the physical elements and
processes that make up the environment: energy, air, weather,
climate,landforms, soils, animals, plants, and Earth itself.
Physical
geography is concerned with Earth’s four “ sphere” and
their interactions.
Atmosphere:
(atmo is Greek for “air”)a
thin gaseous layer that surrounds the earth.
It receives and returns flows of heat and moisture from and to surface.
The atmosphere also supplies vital elements-carbon, hydrogen, oxygen, and
nitrogen-needed to sustain the life-forms on the lands.
Lithosphere: (litho is greek for
“stone”) comprising
the rocks of Earth’s crust. The solid rocks of the lithosophere
bears a shallow layer of soil in which nutrient elements become available to
organisms. The lithosphere is shaped by water, wind etc into different landforms, like mountains,
rivers, plains.
Hydrosphere,
Hydro is Greek for water. So hydrosphere
is all the water substances. Most of water is in the oceans, some exist in
rivers, lakes, or glacials, or atmosphere or in
ground, or in atmosphere.
Biosphere
(biois greek
for “life”) encompasses all parts of Earth where living organisms can exist.
These
four spheres are not separate and discrete but rather considerably
intermingled. Like an ocean, a body that is clearly in major component of the
hydrosphere and yet contain lots of fish which belong to biospher. Soils which is composed largely of bits of
mineral matter (lithosphere) but also contains life forms (biosphere), soil
moisture (hydrosphere) and air (atmosphere).
1. Earth and Sun
1.1. Shape of earth
Everyone
in the class know the earth is a round body. Clearly shown in the
pictures taken from space by astraonauts and by satellite.
But our ancesters do not know this. Like many sailors
thought the earth is like flat disk and their ships would fall off if they
traveled to its edge.
Though
earth is a round body, it is not perfectly spherical, because of the earth rotation, the diameter of earth on equator is 7926 miles
while polar diameter is 7900 miles. So it is slightly bulge
at the equator. The earth’s true shape is described as an oblate ellipsoid.
In
addition, the shape of Earth has obvious deviations from true sphericity that are the result of topographic
irregularities on its surface. Like mountains, oceans, etc.
1.2
Earth’s Rotation.
Earth
spins slowly, making a full turn with respect to the sun every day, we use the term rotation to describe this motion. One
complete rotation with respect to sun defines the solar day. The solar day is
divided into exactly 24 hours.
The
earth rotates on its axis, an imaginary straight line through its center. The
intersections of the axis of rotation and the earth’s surface are defined as
the poles. To distinguishe
between the two poles, one is called north pole and
the other is called south pole.
2. Location and time on Earth
To
determine specifically where something is located on earth’s surface, we use
latitude and longitude
Latitude
is an angular distance north or south of the equator, measured from the center
of Earth.
The
equator is 0 degree and North pole is 90 degree north
latitude and south pole is 90 degree south latitude. So the equator divides the
globe into two equal portions, or hemisphere: north hemisphere and south
hemisphere.
A
line connecting all points along the same latitudinal angle is called a parrallel.
Latitudinal Geographic Zones. Natural
environments differ dramatically from the equator to the poles, in both their
processes and their appearance. As
convenience, geographers identify latitudinal geographic zones as regions with
fairly consistent qualities. These zones are :
equatorial and tropical, subtropical, midlatitude, subarctic or subantarctic, and
arctic or antarctic.
The
tropic of cancer (23.5 north parrel) and the Tropic
of Capricorn (23.5 south parallel) are the most extreme northern and southern
parallels that experience perpendicular (directly overhead) rays of the sun at
local noon; The
Arctic Circle(66.5 north parallel) and the Antarctic Circle (66.5 south
parallel) are the parallels farthest from the poles that experience 24
uninterrupted hours of night during local winter, or of day, during local
summer.
Longitude
Longitude
is an angular distance east or west of a point on Earth’s surface. Measured from the center of Earth. Aline connecting
all points along the same longitude is a meridian. Thus longitude is the name of the angle,
meridian names the line, and both indicate distance east or west of an
arbitrary prime meridian. The prime
meridian is the one passing through the old Royal Observatory at
Longitude
ranges from 0 to 180 degrees, east or west.
When both the latitude and longitude of a place are known, it can be
accurately and precisely located on the geographic grid.
When
arcs of latitude or longitude are measured other than in full-degree
increments, minutes and seconds can be used.
A minute is 1/60 of a degree, and a second is 1/60 of a minute, or
1/3600 of a degree. The latitude 41
degree 27 minutes 41 seconds can be traslates to
41.4614 degree N.
Global
time
Now
in
Earth
revolves 360 degrees every 24 hours, or 15 degree per
hour. Thus, a time zone of 1 hour is established for each 15 degree
increment of longitude So in the
standard time systems, the globe is divided into 24 time zones, so the
difference in time between adjacent zones is normally one hour. In some states
and nations, however, the difference is only one-half hour.Like
When
we take a globe with 15 degree meridians and count them in an eastward,
starting with the
Daylight saving time.
In
many countries, time is set ahead 1 hour in the spring and set back 1 hour in
the fall. A pratice known as
daylight saving time.
In
the United sates daylight saving time comes into effect on the first Sunday in
April and is discontinued on the last Sunday of October.
3. The Earth’s revolution
around the Sun.
So
far, we have discussed the importance of the earth’s rotation on its axis. Another important motion of the earth is its
revolution, or its movement in orbit around the sun.
Each
revolution takes 365 days, 5 hours, 48 minutes and 46 seconds or nearly 365.25.
The path followed by Earth in its journey around the sun is not a true circle
but an ellipse. Because of this
elliptical orbit, the earth-sun distance is not constant. Rather it varies from
91,445,000 miles at perihelion position on January 3 to 94555000 mile at the aphelion position on July 4. The average Earth-Sun distance is defined as
one astranomical unit (1AU) and is 92, 955,806
miles. Earth is 3.3 percent closer to
the Sun during the
Instead,
the season we experience on earth are related to the orientation of the earth’s
axis of rotation and the position of the sun.
We usually describe this situation by stating that the earth’s axis is
tilted. The axis of the earth’s rotation is tilted by 23.5 degree away from a
right angle with the plane of the ecliptic.
In addition, the direction toward which the axis points is fixed in
space-it aims toward Polaris, the north star. The deriction
of the axis does not change as the earth revolves around the sun. As a result, the north pole
is tilted away from the sun during one part of the year and is tilted toward
the sun during the other part.
On
December 22, the earth is positioned so that the north polar end of its
axis leans at the maximum angle away from the sun, 23.5 degrees. This event is called the winter solstice or
December solstice (avoiding confusion because the south hemisphere is summer)
Six
months later, on June 21, the earth is on the opposite side of its orbit, at
this event, known as the summer solstice (june
solstice)
Midway
between the solstice dates, the equinoxes occur: The vernal equinox
occur on March 21 and the autumnal equinox occurs on Sep. 23.
Now
let’s look at another concept. Note that
the earth is always divided into two hemispheres with respect to sun’s rays.
One hemisphere is lit by the sun, and the other lies
in the darkness. The circle that seperates the day hemisphere from the night hemisphere is
called the circle of illumination.
On
the equinox conditions, the circle of illumination passes through the north and
south poles.
The
sun is directly overhead at the point on the earth’s surface is called subsolar point.
At
the June solstice, regions poleward of the arctice experience continuous daylight while the regions poleward of the antarctic
experience continous darkness.
4. maps, Scales and Projectons
A
map is a generalized view of an area reduced greatly in size. The art and science of mapmaking is called
cartography.
A
map includes a scale. The ratio of the
distance on a map to that on the real world is called scale. A 1:1 scale means that a centimeter on the
map represents a centimeter
on the ground. A 1: 24,000
scale means 1 centimeter on map represents 240 meters in the real world.
There
are three ways to represent scale:
1. written scale: simply state the
ratio for example, one centimeter to one kilometer.
2. Representative fraction
(RF) is expressed with either a colon or
a slash, as 1:125,000 or 1/125,000/
3. Graphic scale, or bar scale
is a bar graph with units to allow measurement of distances on the map. An important advantage of a graphic scale is
that, if the map is enlarged or reduced, the graphic scale enlarges or reduces
along with the map. In contrast, written and fractional scales become incorrect
with the enlargement or reduction.
Map
projections
Map
is two dimentional representaions
of our three dimentional Earth. Unfortunately, this
conversion causes distortion.
A
map projection is a system for displaying the curved surface of the geographic
grid on a flat surface.
Polar
Projection
The
polar projection can be centered on either the north or the south
pole. Meridians are straight lines radiating outward form the pole, and
parallels are nested circles centered on the pole.
Mercator projection
The
Mercator projection is a rectangular grid of meridian
as straight vertical lines and parallel as straight horizotal
lines. Meridians are evenly spaced, bu the spacing
between parallels increases at higher latitude so that the spacing at 60 is
double that at the equator. Closer to the poles, the spacing increases even
more, and the map must be cut off at some arbitary
parallel, such as 80 degree north.
Goode
Projection
The
Goode Projection uses two sets of mathematical curves (sine curves and
ellipses) to form its meridians. The Good projection has one important properties- it indicates the truse
sizes of areas of the earth’s surface.