Location and Time on the Earth

Longitudes are angular distances east or west of the prime meridian. Longitudes are also called Meridians. The Prime Meridian passes through Greenwich, in England.

 

Some Important Longitudes include: 

1.     Prime Meridian = Longitude 0^o (Greenwich Meridian).

2.  International Date Line (Longitude 180^o).

 

Characteristics of Longitudes

1.  Each meridian is half of a great circle.

2.  They run in a true north-south direction from

     connecting the North and South Poles.

3.  They are spaced farthest apart at the equator but

     converges at the poles. 

4.  Meridians help us to determine standard time.

 

LATITUDES angular distances East or West of the Equator. Latitudes are also called Parallels.

Longitudes and Latitudes are expressed in degrees, minutes and seconds.

 

Some Important Latitudes:

1.           Equator (Latitude 0^o)

2.           Tropic of Cancer (Latitude 23.5^oN)

3.           Tropic of Capricorn (Latitude 23.5^oS)

4.           Arctic Circle (Latitude 66.5^oN).

5.           Antarctic Circle (Latitude 66.5^oS).

 

Characteristics of Latitudes:

1. Aside the equator, all latitudes are small circles.

2. Always parallel to one another.

3. True east-west lines.

4. Important for the determination of the climatic 

    types of places.

 

A mesh of intersecting Latitudes and Longitudes drawn on a map produce a Geographic Grid, a Reference Grid or Graticule.

Geographic Grid is used to identify locations on the earth. A modern instrument for determining locations is termed Global Positioning System.  

 

A Great Circle is a plane that passes through the center of the earth. (e.g. Equator and all Meridians). The shortest distance between any two points on the earth's surface is attained along the arc of a Great Circle. Small Circles are lines that do not pass through the center of the earth. All Parallels other than the Equator are Small Circles.

 

STANDARD TIME ZONES

The earth undergoes one complete rotation along its axis in 24 hours. For a complete rotation on its axis, the earth passes through 360 degrees. For every one-hour time, a point on the earth moves through 15 degrees of longitude (360/24 hours). For every 4 seconds a point on the earth’s surface passes through 1 degree of Longitude.

 

Earth’s Rotation and Time

The earth rotates in an anti-clockwise direction (From West towards East). Places on the East of a given point on the earth are therefore ahead of time while those places to the West of the same point always lag behind time.

 

The World's Standard Time Zones.

In 1883, the Interstate Commerce Commission of the United States started a system of Standard Time Zones. United States mainland is divided into 4 Standard Time Zones. These are:

1.          Eastern Time Zone (New York or Boston),

2.          Central Time Zone (Chicago)

3.          Mountain Time Zone (Denver) and

4.          Pacific Time Zone (Los Angeles).

 

The International Date Line:

Each new calendar day begins at midnight on the International Date Line (Longitude 180^o). Crossing the line requires adjustments to dates. Traveling from West toward East (e.g. from USA to Japan) one jumps into a new day on crossing the line; Monday 6 a.m. in the US immediately becomes Tuesday at 6.00 a.m. on crossing the line to Japan. 

 

If one travels from East towards West (from Japan to USA), the person looses a day, Tuesday 6.00 a.m. on the other side of the line to Monday 6.00 a.m. on crossing the line into USA.

 

EARTH AND SUN RELATIONS

The earth rotates on its axis completing one rotation every 24 hours. The most important consequence of this rotation is the daily pattern of DAY and NIGHT.

 

Revolution around the sun

The earth also revolves around the Sun on an Orbit which is not a perfect circle. On the Orbit, the earth is closest to the sun on January 3^rd (called PERIHELION), 

 

The Earth is farthest away from the Sun on July 4^th. This position is called APHELION. 

 

Throughout its revolution around the sun, the earth moves through a plane called the PLANE OF THE ECLIPTIC. The earth's axis maintains a constant relationship to the plane at an inclined angle of 23.5⁰ The inclination of the axis during the revolution result in three changes.

a.      different positions of the noon sun in the sky

b.     different position of sun rise and sun set

c.      different lengths of day and night in the year.

 

Equinox.

March 21 is Spring Equinox and September 21 is Autumnal Equinox. On these two days of the year, ALL PLACES on the earth receive approximately 12 hours of daylight and 12 hours of darkness.

 

The Seasons:

June 21^st (Summer Solstice)

On this day, the earth is at a position in its orbit where the North Pole is most directly pointed toward the sun. Places in the Northern Hemisphere receive more sunlight (causing Northern Summer) and the Southern Hemisphere has less Sunlight (Winter).

 

December 21^st (Winter Solstice)

On this day, the Sun moves into the Southern Hemisphere (causing summer there). The Northern Hemisphere receives less sunlight (causing winter).