1. Latitude and Longitude
Finding Your Location on a Sphere
PSC 121 Prince George’s Community College Barbara Gage

2. Coordinate Systems
When you are locating a point on a flat surface you can use Cartesian coordinates of x and y.
The point 2, 3 is plotted on the graph.
y-axis
x-axis

3. Coordinate Systems
When you are locating a point in a 3-dimensional system you can use Cartesian coordinates of x, y, and z.
The image shows the point 3, 2, 2 plotted.

4. Coordinate Systems
When you are working with a curved surface such as a sphere, you need to use a different system, one based on angles (polar coordinates) measured from reference points.
One of our reference points is the center of the Earth.

5. Coordinate Systems
On a body such as the Earth or our moon, we can pinpoint the location of any city or landmark using two values, the latitude and longitude. These are polar coordinates.

6. On the Earth there are two additional sets of reference points.
The Equator divides the Earth into the Northern Hemisphere and the Southern Hemisphere.

7. The Prime Meridian divides the Earth into the Western Hemisphere and the Eastern Hemisphere.

8. Latitude
Latitude is defined as the elevation of the location point above (or below) the equator.
The measurement is expressed in degrees, minutes, and seconds.
The equator is at 0° and the poles are at 90°.

9. Latitude
If the location point is north of the equator an N or + is added to the degrees.
If the point is to the south of the equator an S or – is added to the value.
52°N or +52°
24°S or -24°

10. Latitude
On the Earth we designate lines of equal latitude as parallels.

11. Longitude
Longitude is defined as the measurement of the location point east or west of the Prime Meridian
The value is also expressed in degrees, minutes, and seconds.
Note: There are 60 minutes in a degree and 60 seconds in a minute.

12. Longitude
If the point is located to the west of the Prime Meridian we add a W to the value.
If the point is located east of the Prime Meridian we add an E after the value
30°W
80°E

13. Longitude
On the Earth we designate lines of equal longitude as meridians.
The Prime Meridian has a value of 0° and no E or W. The longitude values increase up to 180° in both directions.

14. On Newer Maps…
As we explore and chart new planets, the way longitude is recorded has changed. Instead of 0-180° E and W, longitude measures start at the prime meridian and continue eastward all the way around the planet. New longitudes values run from 0-360°.

15. Mars Map

16. Venus Map

17. Longitude and Time
When the Sun crosses the meridian that pinpoints your location we say that the time is “local noon”. Shadows are shortest at this time.

18. Longitude and Time
Local noon poses a problem for travelers because it is noon at different times in different locations. That means that timetables are useless.
To solve this problem time has been gauged from the Prime Meridian also called the Greenwich Meridian (since it passes through the Royal Observatory in Greenwich, England).

19. Longitude and Time
If you place meridians 15° apart starting with the Prime Meridian, you will divide the Earth into 24 zones. These correspond to the 24 hours in a day.

20. Longitude and Time
As you travel around the world to the east, you gain an hour in time for each zone you cross. If you travel to the west you lose an hour.

21. But…
If you traveled around the world to the east fast enough you would be a day older in a short time!
If you traveled west you could go back in the past!
To solve this problem it was agreed that the 180° meridian would signal the change of date point.
Travel east and the date goes back one day; travel west and you advance a day when crossing this meridian.

22. But…
To keep all of a country in the same time zone, the International Date Line does not follow the 180° meridian exactly.
Other time zones make the same accommodations for country or state boundaries.