Transcript Measuring the Earth

Measuring the Earth
Chapter 2
Models
• Physical models use observations of
sight to provide us with information.
• Mental models represent ideas or
images of something in your mind.
• Laboratory models are used to
simulate natural events.
• Mathematical models are formulas and
equations.
• Graphical models are used to simplify
relationships between variables.
Size of the Earth
• Eratosthenes, about 200 BC,
made a very accurate
determination of the Earth’s
circumference. (39,000 km)
– The earth’s actual circumference is
equal to 40,076 km.
Earth’s Structure
• The earth is divided into several
parts, or “layers”.
– The top layer, the crust, is about 10km
thick beneath the oceans and 65km
thick beneath the continents.
– The mantle is about 2850km thick.
– The outer core is about 2100km thick.
– The inner core is about 1400km thick.
Earth’s Structure
Outer Spheres
• The outer layer composed of the
lithosphere, hydrosphere, and
atmosphere.
• Lithosphere is the rock near Earth’s
surface that forms continuous solid
shell around the Earth.
• Hydrosphere is the thin layer of water
resting on the lithosphere. (70% of the
Earth’s surface)
• Atmosphere is a relatively thin shell of
gasses, held to the Earth’s surface by
gravity, that surrounds Earth.
Determining Positions on
Earth
• Coordinate systems are grid-like
systems of imaginary lines that
determine locations on Earth’s surface.
• Latitude is the distance, in degrees,
north or south of the equator.
– The Equator is 0o and the North Pole is 90o N
latitude and the South Pole is 90o S latitude.
– Parallels of latitude – all lines are parallel.
– Altitude of Polaris = your latitude.
• Longitude is the distance, in degrees,
east or west of the Prime Meridian 0o
Latitude and Longitude
Measuring Longitude
• Chronometer is an accurate clock
which keeps the time at the Prime
Meridian (Greenwich Mean Time –
G.M.T.) and the solar time at any
other meridian.
• Solar noon is when the sun is a
it’s highest altitude.
Mapping Fields
• Isolines are lines connecting
points of equal value.
– Examples are isobars,
isotherms, contour lines.
• Contour lines are lines on a map
that connect points of equal
elevation.
Gradient
• The gradient, or slope, is the rate
of change of a field quantity
between two places.
• Gradient = change in value
change in distance
Using Topographic Maps
• Topographic maps (contour maps)
show the elevation of various
points on the Earth’s surface.
• The contour interval is the
difference in value between
contour lines;
– The zero contour line is at sea level.
Contour Lines
Topographic Map
Map Features
• Depressions are holes dug into Earth’s
surface and these are shown on a map
by hatchured lines.
• Direction is indicated on most maps by
an arrow to indicate north.
• Map Scale is the ratio of distance on
the map to distance on the earths
surface.
– Ex: 1:63,360 means that one inch on the
map equals 63,360 inches, or one mile, on
Earth’s surface.
Map Features
Profiles
• A profile is a side view of the Earth’s
surface.
Map Profiles
Map Slope
• Map slope, or gradient, is the rate
of change of elevation between
two points.
Gradient = change in value (height)
change in distance (a to b)
The closer lines are together the
steeper the slope.
Different Gradients (Slopes)
Stream Flow
• Streams always flow downhill.
• To determine direction of stream
flow examine the contour lines
wherever a stream crosses them.
– The bends in the contour lines point
upstream.