Longitude specifies the east-west position of a point on Earth. The prime meridian passes through Greenwich, London at 0° longitude and is used as the standard. India uses 82.5° east as its standard meridian. Time zones group countries or regions that share approximately the same local time, typically differing by whole hours. Local time can be calculated by multiplying the difference in longitude from the Greenwich Meridian by 4 minutes or by taking the westernmost and easternmost longitudes of a country and finding the midpoint.

2. 1. LONGITUDE
 DEFINATION- Longitude means the geographic
coordinate that specifies the east-west of a point on
the earth’s surface.
 CHARACTERISTICS-
1. Line of longitudes run north-south but give east-
west locational reference.
2. The length of all the longitudes is same because all
of them are semi circles.
3. The maximum distance between two longitudes is at
equator with a distance of 69.172miles (111.321 km).

3. 4. All the longitudes meet at north pole and south pole
only.
5. The prime meridian is taken as the 0○ longitude or the
0○ meridian.
6. The length of the longitudes from equator exceed to
180○ east in the eastern hemisphere and 180○ west in the
western hemisphere.
7. The distance between two longitudes or meridians
decrease as we go towards the north pole and the south
pole.
8. If we take two opposite longitudes together, it will
form a complete circle around the earth.
9.

4. 2. PRIME MERIDIAN
• Prime meridian is the meridian that passes through
Greenwich, London.
• In 1884, some counties decided that Greenwich should
be the Prime Meridian.
• Prime meridian is located at 0○ longitude.
• Prime meridian is the biggest longitude or meridian
because it is located near the equator.

5. 3. INDIAN STANDARD MERIDIAN
 Indian standard meridian is 82.5○ east.
 British India till 1905 did not adopted the international
standard time zones but in 1905 the meridian passing
through Allahabad at 82.5○ east longitude was picked
as the central meridian for India.
 Corresponding to a single time zone for the whole
country at 5 hours 30 minutes in advance of GMT
(Greenwich Meridian time).

6. 4. TIME ZONES

7.  DEFINATION OF TIME ZONE: Time Zone is mostly
used to refer to the local time of a country or a region.
 There are more than 24 time zones in the world
because normally there is 1 hour difference between
two longitude but some have only half an hour
distance.
 In November 1840, Great Western Railway was the
first company to adopt time zones. The time zone
quickly began to known as railway time.
 In 2 November 1868, New Zealand was the first
country to adopt time zones. The use of time zones
was based on 172○ 30 minutes east longitude, which
means 11 hours 30 minutes ahead of GMT.

8. 5. CALCULATION OF TIME AT LOCAL
MERIDIAN
 FIRST WAY TO CALCULATE TIME AT LOCAL
MERIDIAN:
 It can be calculated by multiplying the differences in
hours from GMT (Greenwich Mean Time)by 15 degrees
per hour. POSITIVE=East, NEGATIVE=West.
 SECOND WAY TO CALCULATE TIME AT LOCAL
MERIDIAN:
 Take the westernmost longitude and the easternmost
longitude of the country and find the nearest multiple
of 7.5 degree. Ex: India’s longitudinal extent is from
68○ 7’ 53”E to 97○ 24’ 47”E. The time at local meridian
comes 82○ 46’ 20”.