EARTH AS A SPHERE

23.1 LONGITUDE

• Great Circles are circles with their centres at the centre of the earth.

• Meridians are semicircles connecting the North Pole and the South Pole, running on the

surface of the earth.

• The longitude of a meridian is determined by

(i)

the angle between the plane of the meridian with that of the Greenwich

Meridian

(ii)

its position to the left or to the right of the Greenwich Meridian.

• The longitude of a given point is written as x0 E or x0 W.

State the longitude for the points given below (NMS is the Greenwich Meridian)

Example:

Greenwich Meridian

Longitude for P = 35οW

Longitude for R = 60οE

a)

Longitude of P =

Longitude of R =

b)

Longitude of P =

Longitude of R =

Earth As A Sphere

1

•

The difference between two longitudes:

o If both longitudes are from the same sides of the Greenwich Meridian, (both E

or both W), then the difference between the two longitudes is the difference of

the angles.

o If the longitudes are from different sides of the Greenwich Meridian, (one E

and the other W), then the difference between the two longitudes is the sum of

the angles.

N

200 W

400 E

Q

P

600

Equator

S

The difference in longitudes = 400 – ( - 200) = 600.

Ex. 2 : Calculate the difference between the two given longitudes.

(Note : Sketch a diagram to help you understand better)

Example

1. 25 o E, 135 0 E

2.

40 0 W , 120 0 W

3.

10 0 E , 90 0 E

5.

125 0 E , 60 0 W

6.

15 0 E , 120 0 W

8.

10 0 E , 100 0 E

9.

115 0 E , 5 0 W

Difference : 1350 – 250 = 1100

4.

135 0 W , 20 0 E

Difference : 200 – (-1350)

=

7.

70 0 W , 10 0 E

Difference :

23.2 LATITUDE

• The Equator is a great circle with its plane that is perpendicular to the axis of the earth.

• Parallels of latitudes are circles with planes perpendicular to the axis of the earth and are

parallel to the equator.

• Latitude is the angle at the centre of the earth...