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Regents Earth Science
Topic II:
Measuring the Earth
Is the Earth Round?
• Not exactly………so Columbus wasn’t
right!
• The Earth appears round but when
“measured”, it is actually flattened at the
poles and bulging at the equator…
….**making the Earth a slightly, slightly,
slightly, slightly Oblate Spheroid
This is not how
It looks!!!!
How can we tell that the shape of
Earth is nearly a sphere?
1. Photographs from space (#1)
2. Masts of ships appearing to “sink” as
they travel past the horizon
3. Gravity Measurements (more
gravitational pull at the poles—closer to
center of Earth = higher weight)
4. Observations of Polaris (the North Star)
Spheres of the Earth:
• Atmosphere: shell of gases that surround
the Earth.
– It is layered into zones. Each zone has a
specific temperature, and composition
• Hydrosphere: all bodies of water on Earth
(oceans, lakes, rivers, ground water)—
covers 70% of Earth’s surface
• Lithosphere: solid portion of the Earth
(rock and soil layer)
ESRT’s Cover
How do you locate Positions on
Earth?
• Coordinate System: a grid of imaginary
lines that are used to locate a point on a
two-dimensional surface (a map)
• Latitude-Longitude System: the most
commonly used coordinate system used
for the Earth. This system is based on
observations of the sun and other stars.
Lines of Latitude (Parallels):
• Measures distance north or south of the
equator (0°
• 90° at Poles
• Parallel
Lines of Longitude (Meridians):
• Measures distances east or west of the
Prime Meridian (Prime Meridian is 0-180 is highest)
• Lines connect at the north and south poles
How do you determine Latitude?
• The angle that Polaris makes with the
horizon is equal to the person’s latitude
(Polaris never moves)
• Altitude = Latitude
Polaris Facts:
• Only seen in the Northern Hemisphere
(not south of the Equator)
• Points Due (exactly) North
• NOT the brightest star in the sky!
• Use Pointer Stars to Find
• Directly above North Pole
“Big Dipper”—easy to see
How do you determine Longitude?
• Find the time difference between your
local time and Greenwich Mean Time
(GMT) and then multiply by 15 (Greenwich
is at 0 Longitude)
– This works because the Earth rotates 15
every hour and the Time Zones are 15
longitude apart (24 total, 1 hour apart)
World Time Zones
• If your time is EARLIER than the time
given for GMT, then you are WEST of the
Prime Meridian
• If your time is LATER than the time given
for GMT, then you are EAST of the Prime
Meridian
U.S. Time Zones
Mapping
• Topographic Maps: shows the shape of
Earth’s surface by using contour lines
(the shape of the lines indicate the shape
of the land)
What are Contour Lines?
• lines of equal elevation (height above sea level)
**there are other lines on other types of maps as
well (Isotherms: equal temperature / Isobars:
equal pressure)
What to look for when looking at
Topographic Maps:
• Contour Interval: difference in height
between two adjacent contour lines
Index Contour: Bold lines
with elevation values
Contour Interval = 20 ft.
• Scale: distances on a map represent the
actual distance on the ground
• Map Direction: often indicated by some
type of arrow pointing north (if there is no
arrow, then north is the top of the map)
• Benchmark: a metal marker placed in the
ground that shows the exact elevation.
..on a topo map, BM X (Elevation)
• Gradient: rate at which a field changes
from place to place—also called slope or
steepness
Change in Field Value
Gradient =
Distance