Download Topic 2: Measuring the Earth

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Topic 2
Measuring the Earth
 Evidence for the shape of the Earth:
- Objects disappear over the horizon from the bottom up
- During lunar eclipses, the Earth’s shadow moves across the face of the moon blocking it out. The shadow
is larger than the moon and curved.
- The altitude of the North Star (Polaris) varies with an observer’s latitude.
- The force of gravity is slightly more at the Poles and slightly less at the Equator.
- Satellite photos from space offer positive proof of Earth’s size and shape
The precise shape of the Earth is referred to as an oblate sphere or oblate spheroid (a squashed sphere),
but this is barely noticeable when considering the vast size of the Earth.
** The best description of the Earth’s shape is a sphere, especially if considered to scale.
 Size of the Earth
Eratostheness’ Method
S
Angle a = Angle a’
a
a’ is some portion of 360
a’
distance S is same portion of
the Earth’s circumference
S
a
------ = -----C
360
Two assumptions:
1) the Earth is spherical
2) the Sun’s rays are parallel
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 Layers of the Earth
The outer parts of the Earth can be divided into 3 major layers: solid, liquid, and gas
Lithosphere: the solid rock shell surrounding the Earth
- extends under the oceans
- includes a covering of soil
- the thin upper layer (10-30 km thick) is called the crust
- the lithosphere averages about 100 km thick
Hydrosphere: the thin layer of water resting on the lithosphere
- includes oceans, lakes, rivers, icecaps, rain, etc.
- shallow compared with diameter of the Earth
- average depth = 4 km
Atmosphere: the layer of gases surrounding the Earth
- extends upwards approximately 700 km, gradually thinning out to space
- stratified (layered) into distinct zones, each with its own characteristics
 Latitude and Longitude
Latitude and longitude are a grid of imaginary circular lines covering the Earth’s surface
Latitude: angular distance north or south of Equator
- reference line = Equator (0) = a line connecting all points midway between the North & South Poles, at a
right angle to the Earth’s axis
- lines measure north and south, but run east-west
- also called “parallels”
- latitude is the same everywhere on a given parallel
- in the Northern Hemisphere, the altitude of Polaris is equal to the observer’s latitude
Longitude: angular distance east or west of the Prime Meridian
- reference line = Prime Meridian (0) = one of the lines connecting the North & South Poles; passes
through Greenwich, England
- lines measure east and west but run north-south
- lines are also called “meridians” or “great circles”
- longitude is the same anywhere on a given meridian
- longitude can be determined by knowing the difference between local noon (for the observer) and noon
at the Prime Meridian (Greenwich Mean Time)
EX/ The Earth rotates 360 in 24 hours, from west to east. 360  24 hrs = 15/hr
So if your longitude is 15 west of the PM, your local noon will occur one hour later than Greenwich
International Date Line: 180 longitude
- marks where each new calendar day begins
- going west: go ahead a day on the calendar
- going east: go back a day on the calendar
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 Fields
field: a region of space in which there is a measurable quantity of a given property at every point
isoline: a line connecting all points of the same value
interval: the value between adjacent isolines
field gradient/slope/rate of change: the rate at which a field quantity changes between points
change in field value
gradient = ----------------------------distance
Rules for drawing isolines:
1.
2.
3.
4.
Every point on an isoline represents an equal value
Isolines are generally smooth lines (no sharp corners)
Isolines are generally parallel to each other
An isoline is an endless line; it either closes upon itself on the map (forming a circle) or at some point
outside the map area
5. Closely spaced isolines represent steep gradients; widely spaced isolines represent gentle gradients
6. Isolines never branch or fork
7. Isolines never cross each other
Determining the direction of stream flow on contour maps:
1) contour lines bend upstream when crossing a stream or river
2) streams/rivers always flow from higher elevations to lower elevations
Depressions are shown by hachured contour lines (small lines pointing in the direction of the low spot)
topographic profile: a side-view or cross sectional view of the land