Lecture3 latlongpost
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Announcements •Review sessions today & Wednesday 4-4:45 pm, room 230
description
Transcript of Lecture3 latlongpost
Announcements•Review sessions today & Wednesday
4-4:45 pm, room 230
Welcome to Earth
You are here
Inner/ Rocky
Outer/Gaseous
No longer
a planet
SU
N
Aphelion: farthest position from Sun (July 4)Perihelion: closest position to Sun (Jan. 3)
Does this seem weird to you?
Earth’s Elliptical Orbit
This drawing is very misleading!
Earth’s Elliptical Orbit
The Earth is RoundAn Oblate
Ellipsoid• Imagine a slightly squished sphere• Satellite observations show us that the
Earth isn’t perfectly round…It’s flattened at the poles and bulging at the equator.
21 km difference
The Earth is RoundAn Oblate
EllipsoidIn 1687, Newton predicted this distortion…
1. As the Earth rotates, the equator moves faster than the poles.
2. The outward force of Earth’s rotation produces a bulge in the equator.
The Geographic Grid System
• provides system (but not a flow system!) for locating places on the Earth’s surface
• divides Earth into imaginary circles parallel and perpendicular to axis of rotation
angular distance north or south of the equatorequator = 0º, poles = 90º
latitude = angle; parallel = line
Latitude
Latitude
The Oregon Boundary Dispute
The 49th Parallel
The 42nd Parallel
Fifty-four Forty or Fight!
Angular distance east or west of a point on the Earth’s surface
Prime Meridian = Greenwich, UK = 0º
longitude = angle; meridian = line
Longitude
Royal Observatory,Greenwich England
Prime Meridian
Prime Meridian
100th MeridianLongitude
Beyond the Hundredth Meridian
Wallace Stegner
Measuring lat and longDMS units• degrees (º), minutes ('), seconds ("),
direction• 60 minutes = 1 degree• 60 seconds = 1 minute
e.g., 41º27'41" N
Decimal units• degrees in decimal format, direction
e.g., 41.4614ºN
Infrared Aerial Photo200 m
37˚ 16’ 12” N37˚ 16’ 12” N
76˚ 42’ 42” W76˚ 42’ 42” W
2”2”9”9”
Measuring lat and longConverting DMS units to Decimal Degrees
• 77º 42' 25"
25" = (25 / 60)' = 0.4167'
• 77º 42.4167'
42.4167' = (42.4167 / 60)º = 0.7069º
• 77.7069º
“Simple” formula (plug & chug)
Dec. degrees = Dº+((M'+(S"/60))/60)
Finding your position on the global coordinate system
Which way is North?
Azimuth/Bearings:North = 0˚ or 360˚
East = 90˚
South = 180˚
West = 270˚
Option 1:
Use a map
Finding your position
Option 2:
Use a map (again)
& take bearingsx Cape Point
Mt. Owensx
N
1 km
Finding your position
Taking Bearings
058˚ to Mt. Owens x Cape Point
Mt. Owensx
N
1 km
x Cape Point
Mt. Owensx
N
1 km
058o
Finding your position
Taking Bearings
058˚ to Mt. Owens
327˚ to Cape Point
x Cape Point
Mt. Owensx
N
1 km
x Cape Point
Mt. Owensx
N
1 km
058ū
Finding your position
x Cape Point
Mt. Owensx
N
1 km
327o
Taking Bearings
058˚ to Mt. Owens
327˚ to Cape Point
Need map & landmarks!
x Cape Point
Mt. Owensx
N
1 km
x Cape Point
Mt. Owensx
N
1 km
Finding your position
But how do you find yourself when land cannot be seen?
Finding your positionSure, now we’ve got GPS and radar.
But how on Earth did the English find Jamestown over and over again?
Use the stars to find your Latitude Use time to find
your Longitude
Astrolabe Sextant
Latitude from the Stars
At the North Pole where is the North Star?
Directly overhead @ 90˚
What is the latitude at the North Pole?
90˚
Latitude from the Stars
North Star
North Pole
Equator
Latitude= 90°
Horizon
At the Equator where is the North Star?
On the horizon @ 0˚
What is the latitude at the Equator?
0˚
Latitude from the Stars
North Star
North Pole
EquatorLatitude
= 0°
Horizon
x = angle of the North Star above the horizon
What is the relationship between x and latitude?
x = Latitude
Latitude from the Stars
North Star
North Pole
EquatorLatitu
de
= x°
Horizon
x
x = angle of the North Star above the horizon
Is there a relationship between x and latitude?
x = Latitude
Latitude from the Stars
North Star
North Pole
Equator
Latit
ude
= x°
Horizon
x
World Time Zones
Longitude from the Time
What time is it in Paris, Texas?~8:30 am
What time is it in Paris, France?~3:30 pm
How many hours in a day?24 hours
How many degrees of longitude on the earth?
360˚
Longitude from the Time
How many degrees of longitude constitute a time zone?
360˚/ 24 hours = 15˚ per hour
So, roughly how many degrees of longitude separate Paris from Paris?
Longitude from the Time
putting it into practice
Longitude from the Time
If 1 hour = 15°what does 1 minute equal?
Longitude from the Time
-divide each side by 60-
1 min (time) = 15 min (longitude)
How’s that for confusing?
