The Earth is a Rotating Sphere - MSU Billings 2009/Suits/Geog... · The Earth is a Rotating Sphere...
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The Earth is a Rotating Sphere
• The Shape of the Earth
• Earth’s Rotation ( and relative movement of the Sun and Moon)
• The Geographic Grid
• Map Projections
• Global Time
• The Earth’s Revolution around the Sun
Earth
The Shape of the Earth
the Earth’s shape is very
close to spherical (oblate
ellipsoid (flattened at the
poles)
Dpolar = 7900 miles
= 12,714 km
Dequator = 7926 miles
= 12,756 km
Radius [r] = Diameter/2
Circumference of a circle = 2r
Area of a circle = r2
Surface area of a sphere = 4r2
Volume of a sphere = 4/3r3
a
b
c
The Earth’s movement results in daily, monthly,
and annual cycles
Diurnal (day/night) cycles are produced by changes in
sunlight resulting from the Earth’s rotation
Annual cycles result from the revolution of the Earth
about the Sun
Seasonal cycles result from the tilt of the Earth’s
rotational axis
Tidal cycles result from interactions between the Sun,
the Moon and the Earth
But first,
Did ancient mariners think
the world was flat?
The direction of
the Earth’s
rotation is
counterclockwise
when viewed
from above the
north pole or
west to east
when viewed
with the north
pole up
Earth Rotation
The Geographic Grid
Cartography
Earth is an oblate ellipsoid (flattened at the poles)
divided into degrees, 60 minutes and 60 seconds
provides a “grid” of imaginary lines (parallels and
meridians)
IG4
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4
b) Longitude (Meridians) 1 degree
of longitude = 111 km at the
equator and 0 at the poles
The Geographic Grid
a) Latitude (Parallels)
1 degree latitude = a constant 111 km
Figure 1.3, p. 28
Latitude is the angle
between a point on a
parallel and the centre
of the Earth and a
point on the equator
Longitude is the angle
between a point on a
meridian and the
centre of the Earth and
a point on the Prime
Meridian
The Geographic Grid
Figure 1.5, p. 29
The Prime Meridian,
The Greenwich Observatory
London, England
Revolution
• one complete circling around the Sun
• from above north pole in counterclockwise direction
• the path is not circular but is very slightly elliptical
• all planets orbit on the plane of the ecliptic
E
The Earth’s Revolution around the Sun
SUN
Figure 1.14, p. 38
The Earth’s Revolution around the Sun
the Earth and Moon both rotate and revolve in a
counterclockwise direction (when viewed from a point over the
Earth’s north pole)
sun is not in the middle of the plane of the ecliptic
SUNE E
variation in distance of ~ 3%
Aphelion - the Earth
furthest away from Sun
(July 4)
Perihelion - the Earth
closest to Sun
(January 3)
The Earth’s Revolution around the Sun
152 million km 147 million km
The earth’s axis
is tilted
66.5° to the
plane of the
ecliptic
or from the
perpendicular to
the plane of the
ecliptic by 23½°
Earth Rotation
Figure 1.16, p. 40
the Earth rotates about its axis from west to east once every 23
hours and 56 minutes
the Earth’s axis points same way (parallelism) as it revolves
around the sun
The Earth’s Revolution around the Sun
The Earth’s Revolution around the Sun
at equinox, the
circle of
illumination
passes through
both poles
the subsolar
point is the
equator
each location on
Earth
experiences 12
hours of sunlight
and 12 hours of
darkness
Figure 1.18, p. 41
The Earth’s Revolution around the Sun
Solstice (“sun stands still”)
On June 22, the subsolar point is 23½°N (Tropic of Cancer)
On Dec. 22, the subsolar point is 23½°S (Tropic of Capricorn)
Figure 1.19, p. 41
The Earth’s Revolution around the Sun
the latitude
of the
subsolar
point marks
the
sun’s
declination
which
changes
throughout
the
year
Figure 1.20, p. 42
Solstice & Equinox
• Earth's tilt of 23.5° and revolution around the sun creates seasonal solar exposure and heating patterns
• At solstice, tilt keeps a polar region with either 24 hours of light or darkness
• At equinox, tilt provides exactly 12 hours of night and 12 hours of day everywhere
the four seasons occur because the Earth maintains a constant
orientation (tilted 23½° with respect to the perpendicular to the
plane of the ecliptic) as it revolves around the sun
The Earth’s Revolution around the Sun
Figure 1.17, p. 40
http://www.geog.ucsb.edu/~joel/g110_w08/lecture_notes/sun_angle/anim_fall.gif
http://www.geog.ucsb.edu/~joel/g110_w08/lecture_notes/sun_angle/anim_sum.gif
Local Solar ChangesNorthern
hemisphere sunrises are
in the southeast
during winter, but in the
northeast in summer
Summer noon time sun is also higher above the
horizon than the winter
sun
based on the east-west position of the Sun
a solar day defined by one sun circuit
solar noon (at a particular location) is the time of the
highest solar angle
the time is calculated by the position of the Sun at
selected meridians (Standard Time)
Global Time
the Earth rotates 15° per hour so time zones differ by 1 hour
(360°/15° = 24 hours)
Global Time
Figure 1.12, p. 36
Different days are observed on either side of the International
dateline (180th meridian = 15° X 12 hours), 12 hours
difference from the Prime Meridian
Global Time
Figure 1.13, p. 37
To make a map you need a Map Projection
3 properties to consider: scale, area and
shape
Map Projections
Map ProjectionsPolar Projection
centered on north or
south pole
meridians are
radiating straight lines
parallels are
concentric circles
spacing of parallels
(scale fraction)
increases outward
from the pole
Map ProjectionsMercator
Projection
rectangular grid of
meridians (straight
vertical lines) and
parallels (straight
horizontal lines)
meridians are evenly
spaced, spacing of
parallels increases
with latitude
straight line on map
represents true
compass direction
(bearing), i.e. for
navigation
Used to show surface
flows, e.g. weather,
oceans
Map ProjectionsGoode Projection
two sets of mathematical curves used to define its meridians
indicates the true sizes of the Earth’s surface but distorts the shapes of areas
Used to show land features
Figure 1.10, p.32
Modern Cartography and GIS
GIS = Geographic Information System
a computer-based system that allows maps,
diagrams, satellite images and aerial photographs to
be stored and manipulated
uses geographically referenced data (e.g.
projections)
spatially-referenced data can therefore be used to
solve complex planning problems.
Map Projections
GIS data layers: for
each map layer, the
geographic location of a
point on the Earth’s
surface must coincide
(georeferencing)
Example:
Map Projections
p. 35http://ahps2.wrh.noaa.gov/ahps2/index.php?wfo=byz&view=1,1,1,1,1,1,1,1&toggles=10,7,8,2,9,15,6