1. Locating Positions on Earth

2. Sydney, Australia = 34°0’S, 151°0’E
Coordinate Systems
A coordinate system is a method of locating a position on a 2-dimensional surface using two numbers (called coordinates).
Earth scientists use the latitude-longitude coordinate system to identify locations on Earth’s surface. Latitudes and longitudes are measured in degrees (°) and minutes (‘). Each degree (°) is made up of 60 minutes (‘).
Sydney, Australia = 34°0’S, 151°0’E

3. Parallels = lines of latitude that “parallel” that of the equator.
Latitude is the angular measurement north or south of the equator.
The equator (0°) marks the middle of the Earth –halfway between the North and South poles.

4. Latitude
The latitude of any point on the Earth is the angular measurement between the location and the equator using the center of the Earth as a focal point.
Latitude measurements above the equator are referenced with an “N” for Northern Hemisphere.
Latitude measurements below the equator are referenced with an “S” for Southern Hemisphere.

5. This observer is located at 20°N latitude.
Measuring Latitude
Scientists may use the position of stars in the night sky to determine the latitude of their position on the Earth’s surface.
Polaris (The North Star) is seen by observers in the Northern Hemisphere. The star is positioned in the night sky nearly directly over the North Pole.
By measuring the angle between an observer’s view of Polaris and the horizon, one can determine the latitude they are at in the Northern Hemisphere..
This observer is located at 20°N latitude.

6. The observer is located at 40° N latitude.
A sextant is an instrument used by an observer to determine the angle between Polaris and the horizon.
Measuring Latitude
Pointer stars in the “Big Dipper” constellation allow the viewer to find Polaris .
Polaris
The observer is located at 40° N latitude.
40°
observer
horizon

7. Meridians = “semi-circle” arcs of longitude on the Earth’s surface the connect the North and South poles.
Longitude
Longitude is the angular measurement east or west of the prime meridian.
The prime meridian (0°) marks the middle of the Earth –halfway between the Eastern and Western Hemispheres.

8. Longitude
Western Hemisphere
Eastern Hemisphere
The meridian that passes through Greenwich, England has been designated as the prime meridian (0°).
The longitude of any location on the Earth’s surface is the number of degrees between the location and that of the prime meridian.
Longitudes increase east and west from the prime meridian to the International Date Line (180°)
Longitude measurements east of the prime meridian are referenced with an “E” for Eastern Hemisphere.
Longitude measurements west of the prime meridian are referenced with a “W” for Western Hemisphere.

9. The Earth rotates at a rate of 15° per hour from west to east..
Measuring Longitude
The longitude of a position on Earth’s surface can be determined if one studies the rate of Earth’s rotation over time.
The Earth rotates at a rate of 15° per hour from west to east..

10. 0°
12 pm
Measuring Longitude
Scientists will use GMT = Greenwich Mean Time as a means by which to gauge the local time and location of longitude for an observer.
15°E
1 pm
15°W
11 am
For example, if the sun has reached its highest altitude in the sky (local noon – 12 pm) at Greenwich, it will be 11am at 15° W and 1pm 15°E.
Remember*** The Earth rotates from west to east at a rate of 15° per hour.

11. Measuring Longitude – Sample Problem
“If it 6 pm at Greenwich England, at which location would it be 10 pm?” D B A C