Geographic Location & Time

Lab 1

Concepts

The Earth’s Grid Latitude/parallels Longitude/meridians Prime Meridian, Equator Great and small circles

Time and Time Zones International Date Line

Grid System: Latitude & Longitude Latitude

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

Grid System: Latitude & Longitude 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

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’

Grid System: Latitude & Longitude

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.

Grid System: Latitude & LongitudeWhen 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

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.

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).

Great or Small Circle?You Decide

What are meridians?

What are parallels?

What is unique about the Equator (relative to all other parallels)?

Great Circle: example

Tokyo,Japan

Atlanta

The shortest path from Atlanta to Tokyo would flyyou through Canada, over Alaska, and down thePacific Rim. You would not pass straight acrossthe US and over the Pacific!

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

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.

Time (con’t)

Time is 1 hour earlier when moving East to West

Los Angeles Denver Chicago Atlanta

PST MST CST EST

5pm 6pm 7pm 8pm

W E

Note: EST is 5 hours “behind” (earlier) than GMT.If it is 8pm EST, what time is it in Greenwich?

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

165oE

Tuesday

5 am

165oW

Monday

7 am

150oE

Tuesday

4 am

150oW

Monday

8 am

180o

Tues.

6 am

Mon.

EastWest