This is a presentation on the chapter-2 of ICSE class 9 ,"Latitudes and Longitudes" by Mrs. Paromita Ganguly of St. Xavier's School, Durgapur, shared by Soumik Saha. Hope it would be helpful. Thank you

1. Unit -1 – OUR WORLD
Chapter – 2
GEOGRAPHIC GRID
LATITUDES AND
LONGITUDES
Continuation – ii

2.  A Longitude is the angular distance of a place east or west of the Prime
meridian.
 Prime meridian is the Central most longitude which divides the earth into
Eastern and Western Hemispheres.
 The value of Prime meridian is 0∘
. It passes through the Greenwich observatory
in London.
 Lines of longitude are called Meridians of longitudes because all places along
the same meridian of longitude experience noon or mid-day at the same time
CONCEPT OF LONGITUDE AND IT’S CHARACTERISTICS
 All meridians of longitude converge at the Poles and are of equal length. They
are suffixed with East and West.
 Individually all lines of longitude are semi circles, but two diametrically
opposite lines make a full circle or a Great Circle.
 There are 180 meridians to the East and 180 meridians to the West. The line
180 ∘
E and 180 ∘
W is the same meridian.
 The distance between two lines of longitude decreases gradually towards the
poles. The distance is maximum at the equator (111 km).
 180∘
meridian of longitude is termed as the International Date Line.

3.  Earth covers 360 longitudes in 24 hours, as it rotates from West to East.
360
24
= 15∘
longitude in 1 hour or, 1∘
longitude in
60
15
= 4, in every four minutes.
 Time increases towards the east and decreases towards the West as earth
rotates from west to east.
 For 1∘
longitude towards the east, 4 minutes are added and for 1∘
longitude
towards the west 4 minutes are subtracted.
LONGITUDE AND TIME
How to calculate time?
Follow the example given below
0
∘
140
∘
E Longitude difference is (140∘
- 0∘
)=140∘
For 1∘
longitude difference the time difference is 4 min
For 140∘
longitude difference, time difference will be 4*140
= 560 min = 560/60 = 9 hrs 20 mins.
∴ Time in Tokyo is = 12 noon + 9hrs 20 min = 21:20 hrs or,
9:20 Pm (Monday).
Greenwich
Time: 12 noon
Day: Monday
Tokyo
Time: ?
Day: ?

4. DIFFERENCE BETWEEN LINES OF LATITUDE AND LONGITUDE

5.  It is obtained by overhead sun at noon. For one-degree difference in
longitude, time varies by 4 minutes.
 If a nation follows local time, which varies from place to place it,
would create confusion. Therefore, one Central meridian of a country, on
which a very important city is located is accepted as standard Meridian
of that country.
 The standard Meridian is selected in such a way that it is divisible by
7
∘
30′, so the standard time differs from Greenwich Mean time by
multiples of half an hour (30 min).
 Uniform time followed throughout a country is called a country’s
standard time.
LOCAL and STANDARD TIME
Standard
time
Local Time

6.  Indian Standard Meridian passes through 82∘
30′ E. It passes through Allahabad and close to
Chennai.
 Indian Standard time (IST) is 5hrs 30min ahead
of Greenwich Mean Time
 The time fixed with reference to Greenwich
observatory in London, that is, 0
∘
longitude is
called the GREENWICH MEANTIME or GMT
INDIAN STANDARD TIME AND GREENWICH
MEANTIME
Greenwich MeanTime
Indian Standard Time