1. Geographic Location & Time
Lab 1

2. Concepts The Earth’s Grid Time and Time Zones Latitude/parallels
Longitude/meridians
Prime Meridian, Equator
Great and small circles
Time and Time Zones
International Date Line

3. Grid System: Latitude & Longitude
a.k.a “Parallels”
Each line runs parallel to all the others. They are equally spaced apart and never cross.
0o = Equator
Maximum extent
90oN at North Pole
90oS at South Pole
Lines run east to west but measure distance north and south

4. Grid System: Latitude & Longitude
a.k.a “Meridians”
Lines converge at the poles
0o = Prime Meridian
Maximum extent
180o… also called the International Date Line
Lines run north to south but measure distance east and west

5. Grid System: Latitude & Longitude
Degrees are subdivided into minutes and seconds. The more detailed your location information is, the more accurate it is.
O = degree symbol
’ = minute symbol
” = second symbol
1 degree = 60 minutes (1o = 60’)
1 minute = 60 seconds (1’ = 60”)
Note: minutes and seconds cannot exceed the value of 60.
e.g., 75’ is incorrect. Should be written as 1o15’

6. Grid System: Latitude & Longitude
Always label your latitude and longitude!
Latitude labels = N or S
Longitude labels = W or E
Latitude
Degrees range from 0o (at Equator) to 90o N or S. Cannot exceed a value of 90.
Longitude
Degrees range from 0o (at Prime Meridian) to 180o (International Date Line). Between those spots, a location is either W or E of the Prime Meridian. Cannot exceed a value of 180o.

7. Grid System: Latitude & Longitude
When identifying locations…
Latitude comes before longitude
Get as detailed as possible (at least degrees and minutes).
e.g., Atlanta’s location is: 33°45' N, 84°42′ W

8. Great Circles
A sphere divided exactly in half by a plane which passes right through its center.
The largest possible circle you could manage to draw on that sphere's surface
Despite the curved appearance on flat maps, great circle routes are the shortest distance between two points on Earth.

9. Small Circles
A circle produced by planes passing through a sphere anywhere except through its exact center.
Smaller than a great circle (hence the clever name).

10. Great or Small Circle? You Decide
What are meridians?
What are parallels?
What is unique about the Equator (relative to all other parallels)?

11. Great Circle: example
The shortest path from Atlanta to Tokyo would fly
you through Canada, over Alaska, and down the
Pacific Rim. You would not pass straight across
the US and over the Pacific!
Tokyo,
Japan
Atlanta

12. Time Standard Time: legal time in an area
24 Standard Time Zones in the world
Spaced 15o longitude apart, or 7.5o on each side of a Central Meridian
GMT = Greenwich Mean Time
a.k.a. UTC = Coordinated Universal Time
The Prime Meridian runs directly through Greenwich, England (just outside of London).
Time zones are typically referenced from GMT/UTC.
“Zulu” time = military time (24 hr clock) based in Greenwich
e.g., “1000Z” = 10am in Greenwich
e.g., “1500Z” = 3pm in Greenwich
EST = Eastern Standard Time

13. Central Meridians & Time Zones
Prime Meridian (0o)
EST is based on the 75oW meridian. There are 7.5o longitude on either side of the meridian, making the time zone 15o longitude wide.

14. Los Angeles Denver Chicago Atlanta
Time (con’t)
Time is 1 hour earlier when moving East to West
Los Angeles Denver Chicago Atlanta
PST MST CST EST
5pm pm pm pm W E
Note: EST is 5 hours “behind” (earlier) than GMT.
If it is 8pm EST, what time is it in Greenwich?

15. International Date Line
180o meridian (does not have a W or E label, just simply 180o)
When crossing W to E, it becomes the previous day
When crossing E to W, it becomes the next day
180o
Tues.
6 am
Mon.
150oE
Tuesday
4 am
165oE
Tuesday
5 am
165oW
Monday
7 am
150oW
Monday
8 am
West
East