Unit I: Earth Dimensions
Review Book pp.19-30
Objective #1
• Describe the actual shape of the Earth and
explain 3 pieces of evidence for its actual
shape.
Earth’s Shape
• The Earth appears to be the shape of a
sphere (round in circumference) when
observed from space or scaled down to a
model such as a globe.
Taken from http://earthobservatory.nasa.gov/IOTD/view.php?id=8108 on 8/30/11.
• However, by actual measurement, the
Earth is not a perfect sphere.
• Instead it has an oblate shape, having a
larger circumference around the equator
than through the poles.
Taken from http://scienceblogs.com/startswithabang/2010/11/weekend_diversion_save_the_wor.php on 8/30/11.
Equatorial circumference = 40,076 km
Equatorial diameter = 12,756 km
Polar circumference = 40,008 km
Polar diameter = 12,714 km
Taken from ccrpc.org on 8/30/11.
• Therefore the
Earth is slightly
“bulged” at the
equator and
slightly
“flattened” at the
poles.
• Thus the true
shape of the
Earth is best
called an oblate
spheroid.
Taken from http://www.onr.navy.mil/focus/spacesciences/observingsky/precession2.htm on 8/30/11.
Evidence for the Shape of the Earth
Taken from http://astrobob.areavoices.com/2009/02/17/spectacular-photo-inspires-a-northern-journey/ on 8/30/11.
Animation
• Observations of the North Star (Polaris)
• Polaris lies in space practically over the
geographic north pole of the Earth.
• Altitude
– Angle above the horizon measured in degrees.
• Latitude
– Position north or south of equator in degrees.
Taken from http://oxford-materialstechniques.com/data/illust/019920568X/019920568X.latitude.1.jpg on 8/30/11.
Taken from http://www.nmm.ac.uk/upload/img/altaz-star2.jpg on 8/30/11.
• If Earth is a perfect
sphere, the altitude of
Polaris should be equal
to the latitude of the
observer on Earth.
• These two
measurements are not
exactly the same so
therefore, Polaris gives
evidence that Earth is
not a perfect sphere;
but instead it is slightly
out of round or oblate.
Taken from http://bdaugherty.tripod.com/gcseAstronomy/images/fifty.jpg on 8/30/11.
Kid on a Bike
Photographs of Earth from Space
• When photos of the Earth taken in space are
precisely measured, they show the Earth to be
larger at the equator and flatter at the
geographic poles.
• However, when drawn to scale on a piece of
paper, the Earth appears to be perfectly round.
Taken from http://earthobservatory.nasa.gov/IOTD/view.php?id=8108 on 8/30/11.
Gravimetric (Gravity) Measurements
• Gravity
– Force of attraction between any 2 objects
• Since Earth has a large mass, smaller
objects with less mass are pulled towards
the Earth.
Taken from http://www.bbc.co.uk/schools/ks2bitesize/science/images/earth_gravity.gif on 8/30/11.
• Law of Gravitation
– Gravitational force is proportional to the
inverse square of the distance between 2
centers of attracted objects.
Taken from http://www.physicsclassroom.com/class/circles/u6l3c2.gif on 8/30/11.
• So therefore, gravity and weight of an
object anywhere on the surface of the
Earth should remain the same (if the Earth
is a perfect sphere).
Taken from http://xamplified.com/wp-content/uploads/2009/02/acceleration-due-to-gravity1.jpg on 8/30/11.
• Precise measurements show that gravity
does on remain the same.
• Objects located at the poles weigh more
than the same object located at the
equator. This difference is more than can
be expected due to the centrifugal effect.
Taken from http://www.mrsciguy.com/sciimages/weight.jpg on 8/30/11.
• Centrifugal effect
– Produced by Earth’s rotation, pushes objects
away from the center
• Examples
– Amusement park rides like Gravitron or
Round Up
– Spinning bucket of water trick (here)
Taken from http://home.bway.net/rjnoonan/humans_in_space/gravity.gif on 8/30/11.
Taken from http://startswithabang.com/?p=1718 on 8/30/11.
Taken from http://www.pswleisure.co.uk/images/Fairground/Large/roundupfairground-ride.gif on 8/30/11.
Objective #2
• Name the 3 spheres of the Earth and
describe their unique characteristics.
• Be able to use ESRT p.14 to describe the
atmosphere.
Spheres or Parts of the Earth
The atmosphere extends several hundred km above the Earth’s
surface into space and is the least dense of the 3 spheres.
• Atmosphere
• Hydrosphere
• Lithosphere
Taken from need-media.smugmug.com on 8/30/11.
Earth’s Atmosphere
Atmosphere is the Air
• The atmosphere is stratified (layered) into 4 zones
each possessing distinct characteristics. ESRT p.14.
Troposphere
• Most dense layer of
atmosphere
• Lowest section of the
atmosphere found
between the Earth’s
surface and the
tropopause
• It is characterized by
decreasing temperature
with increasing altitude.
• The only zone of the
atmosphere to contain
water vapor.
Stratosphere
• Region above the
troposphere and
below the
mesosphere
where temperature
increases with
altitude due to the
presence of
ozone.
Mesosphere
• Found above the
stratopause and
below the
mesopause.
• Characterized by
temperatures
that decrease
with an increase
in altitude.
Thermosphere
• Lease dense layer
of atmosphere
• Outermost zone
found between
mesopause and
outer space where
temperature
steadily increase
with altitude.
•According to ESRT p.14, what happens to
Atm. Pressure as you increase in altitude
through each of the zones?
•Atmospheric pressure constantly decreases.
Note that the
temperature
“pauses” then
reverses direction
when switching
from one layer to
the next.
Now you know
why they call it
the “Tropopause.”
Earth’s Hydrosphere
Hydro means water, think hydrant or
hydroelectric.
What is Earth’s nickname?
Taken fromhttp://www.waterdeva.com/blog/wp-content/uploads/blue-planet.jpg on 8/30/11.
• Approximately 71% of the Earth’s surface
is covered with a relatively thin layer of
water. (More dense than atmosphere)
• Includes marine (salt water) and
freshwater (inland lakes and rivers).
Earth’s Lithosphere
Lithosphere is Land
• Lithosphere
– Continuous, outer solid rock shell of the Earth
• The lithosphere is often under the hydrosphere
(More dense) and accounts for the general
features such as mountains, valleys and the
ocean floor.
Taken from http://www.physicalgeography.net/fundamentals/images/lithosphere.gif on 8/30/11.
Objective #3
• Describe a coordinate system and be able
to use latitude and longitude (degrees &
minutes) to determine a position on Earth.
Earth Positions
• Coordinate System
– Uses a grid of imaginary lines and two points
called coordinates.
• A fixed point can be located on a graph by
identifying the axes ( the intersecting point
of two lines).
Taken from http://www.euclideanspace.com/threed/solidmodel/geospatial/ellipsoid/earth.gif on 8/30/11.
What is the most commonly used coordinate
system for identifying points on Earth’s surface?
• Latitude and Longitude
Axes used are called parallels & meridians. Coordinate
system based on observations of the Sun & other stars.
Parallels of Latitude
• The equator, located halfway between the
geographic poles, is a circle which divides the
Earth into the Northern and Southern
hemispheres.
• Lines called parallels are drawn.
These parallels decrease in size
from the equator (0o) to the
North Pole (90oN) and the
South Pole (90oS).
Taken from http://www.smallboatgps.com/class/index_files/image002.gif on 8/30/11.
Meridians of Longitude
• Lines connecting the North
Pole and South Pole are
called meridian.
• The Prime Meridian runs
through Greenwich, England
and has a longitude of 0o.
Longitude is measured using
the meridians, east or west of
the the Prime Meridian (0o) to
a maximum of 180o (the
International Dateline).
Taken from http://www.sailingissues.com/nav2n.png on 8/30/11.
Latitude & Longitude Measurements
• Latitude and Longitude are measured in
degrees.
• Latitude is degrees north or south of the
equator. Longitude is degrees east or west
of the Prime Meridian.
Taken from math.nus.edu.sg on 8/30/11.
• Latitude is often determined by using the
altitude of Polaris above the horizon in the
Northern hemisphere. In the Southern
hemisphere, other stars are used.
Taken from http://astrobob.areavoices.com/2009/02/17/spectacular-photo-inspires-a-northern-journey/ on 8/30/11.
• Longitude is based on the Sun.
• The Earth rotates from west to east, 360o
in a 24 hour period of time.
• How many degrees is that every hour?
Taken from resonanceswavesandfields.blogspot.com on 8/30/11.
Objective #4
• Be able to relate longitude positions and
time differences.
Comparing local time to GMT or UT
allows you to find your longitude.
• Every hour difference from GMT indicates
15o difference in longitude from the Prime
Meridian.
• Each hour earlier than GMT indicates 15o
west of Prime Meridian.
• Each hour later than GMT indicates 15o
east of Prime Meridian.
earlier
later
U.S. Time Zones
Taken from http://www.socialstudiesforkids.com/graphics/timeszones_us.gif on 8/30/11.
Taken from http://wiki.naturalfrequency.com/files/wiki/solar/time-zones.gif on 8/30/11.
• Example:
– A clock indicates it is 4 hours later than GMT.
What is your longitude?
• Modern navigational techniques such as
GPS (Global Positioning System) uses
signals from both Earth and orbiting
satellites to determine latitude and
longitude.
Taken from http://www.colorado.edu/geography/gcraft/notes/gps/gif/figure05.gif on 8/30/11.
Objective #5
• Be able to read and use field (contour or
topographic) maps.
Objective #6
•Know the following terms and be able to
apply them to a map: field, isolines,
gradient, contour interval, hachure marks
Position Charactertistics
• Field
– Region of space that contains a measurable quantity
at every point.
• Examples/Types of Fields
•Gravity
•Magnetic
•Atmospheric Pressure
•Relative Humidity
•Temperature
•Pollen Count
•Snow Cover or Depth
Sample Field Model
• Isolines
– Connect points of the
same value
• Isobars
– Lines connecting
points with same
atmospheric pressure
Taken from http://www.mrsciguy.com/sciimages/isoline.gif on 8/30/11.
• Contour lines
– Lines connecting
points with same
elevation
Taken from weather.com on 8/30/11.
Taken from topozone.com on 8/30/11.
• Isotherms
– Lines connecting
points with same
temperature
Taken from http://www.nc-climate.ncsu.edu/secc_edu/images/IsobarsIsotherms.gif on 8/30/11.
• Isolines represent field characteristics in …
• 2 dimensions.
• Isosurfaces represent field characteristics in …
• 3 dimensions.
Taken from
https://www1.nga.mil/kids/geoint/photodict/PublishingImages/
dict-contourlines.jpg on 8/30/11.
Taken from http://www.berneda.com/teechart_vcl_features/images/SeriesTypeIsoSurface.PNG on 8/30/11.
Taken from http://www.geoblox.com/images/jetty_image.jpg on 8/30/11.
Taken from
http://img.tgdaily.net/sites/default/files/imagecache/story_slid
er/stock/450teaser/space/galaxy_simulation.jpg on 8/30/11.
• Isoline maps and isosurfaces are
examples of models. What is a model?
• Simplified representation of objects,
structures or systems.
Field Changes
• Static
– Unchanging
• Dynamic
– Constantly changing
• Of these two terms, which one describes
almost all fields?
– dynamic
Objective #7
• Use the gradient formula to solve
problems.
• Gradient
– Average slope within field, shows rate of
change of field from one place to another
• Formula
– ESRT p.1
Gradient Example
• Solve using 3 step method (Formula,
Substitution & then answer with label).
• Calculate the pressure gradient along a straight line
between point A and point B on the map. Solve using the
3 step method.
• When isolines are closer together the
gradient is steep and when the isolines are
further apart, the gradient is shallow (less).
Contour (Topographic) Map
• Uses isolines (contour lines) to connect points of same
elevation, usually based on sea level measurements.
Taken from http://www.adirondacknorthway.com/maps/mtmarcySm.jpg on 8/30/11.
• Generally every 5th line is an index contour line.
These lines are printed darker and give the
elevation value.
Taken from http://www.therockerbox.com/Contour_Lines_A3.jpg on 8/30/11.
• Contour interval
– Difference in elevation between two
consecutive contour lines.
• Hachure marks indicate downward slope
and are represented by the following
symbol……..
• ┴┴┴┴┴
What advantage is there to using a topographic
map rather than an ordinary road map?
Taken from http://pics.city-data.com/topo/tpc15669.png on 8/30/11.
• Topos show terrain or land surface.
Objective #8
• Make a profile from a contour map.
What is a profile?
• Vertical cross-section
of land surface
between 2 points on
a map.
• a “side-view” of map
Steps for making a profile.
1. Place straight edge of scrap paper between
the 2 points on the map.
2. Wherever contour line meets edge of paper,
place a mark on scrap paper and record
elevation of that point.
3. Take scrap paper with all the marks against
horizontal axis of graph.
4. Above each mark on scrap paper, plot point on
graph according to vertical axis.
5. Connect all points with smooth line.
(Remember to curve all peaks and valleys!)