LONGITUDES - CBSE Class VI Social Science - Geography
LONGITUDES -
CBSE Class VI
Social Science -
Geography by
Soma Mukhopadhyay for SuccessCDs
Education
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About this
Video:
LONGITUDES
Longitude describes the location of a place on the earth
...east or west of a north to south running imaginary line called the prime meridian.
The lines of longitude are lines running north - south through the poles.
Longitude is the number of degrees east or west of the prime meridian (zero degree) which passes through
Greenwich (England).
Lines of longitude are measured from the centre of the earth.
These lines divide the world up into segments.
The prime meridian (zero degree) and the
180th meridian(at
180 degree longitude) is a great circle that divides the earth into the EASTERN and the WESTERN hemisphere.
The 180 degree longitude line is also referred to as the international date line.
MERDIANS
Longitude is defined in terms of meridians which are half circles running from pole to pole.
The meridians are numbered up to 180 degree to the east and west of the line of 0 (
Zero) degree longitude or the prime meridian
The value of a meridian is followed by the letter 'E' or 'W'.
180 degree E and 180 degree W meridians are the same.
There are
360 meridians in total.
The word meridian means the highest position of a star or the sun which reaches its highest position at midday.
A line of longitude is called a meridian of longitude because all places located on it have midday at the same time.
Meridians are not parallel
..they come together at the poles.
EARTH'S
GRID
THE PARALLELS AND MERIDIANS
FORM A
MESH OR A GRID.
THE GRID IS FOUND ON
FLAT MAPS AND GLOBES.
LONGITUDE AND
TIME
AS THE EARTH TURNS THE
SUN APPEARS TO
MOVE ACROSS THE
SKY.
THIS MOTION GIVES US
DAY AND
NIGHT.
OUR
GLOBAL TIME SYSTEM IS ALSO ORIENTED TO THE SUN.
EVERYDAY THE SUN RISES IN THE
EAST AND
SETS IN THE
WEST. THIS MOVEMENT IS CAUSED BY THE ROTATION OF EARTH FROM WEST TO EAST. THERFORE
PLACES TO THE EAST OF A GIVEN LONGITUDE WILL HAVE
SUNRISE FIRST.
The earth takes 24 hours to cover 360 meridians.
This means that it covers 360/24= 15 degree meridians in 1 hour ... or one meridian in 4 mins (60 mins/15)
BASED ON THIS CALCULATION THE DIFFERENCE IN TIME OF DIFFERENT PLACES IS CALCULATED.
TIME ZONES
EARLIER
PEOPLE THOUGHT THAT THE WHOLE
WORLD SHOULD
SET THEIR
CLOCK AT THE SAME TIME .....................
BUT THIS WAS NOT POSSIBLE AS THE SUN
DOES NOT
SHINE ON ALL PARTS OF THE WORLD AT THE SAME TIME.
In 1884 scientist solved this issue by dividing the world into 24 time zones. Each zone is approximately 15 degree longitude wide.
Greenwich England was chosen to be the location for universal time because its located along the prime meridian.
The time in each zone is calculated by this universal time, also known as the GREENWICH
MEAN TIME.
For e.g.: CHICAGO is
GMT minus 6 hrs....so when its 7 pm in GREENWICH (7-6=1) ,it is
1 pm in CHICAGO.
Local time
The local time of a place is fixed on the basis of the apparent movement of the sun.
When the sun shines exactly Overhead it is mid day or 12 noon at that place.
Mid day occurs at different times at different meridians...... so the local time varies from one meridian to another.
STANDARD TIME
It is the time in any of the 24 time zones (each an hour apart) into which the earth is divided.
The
Indian standard time is the time observed throughout
INDIA or SRILANKA.
The
IST is calculated on the basis of 82 ½ degree E longitude which is just WEST of the town MIRZAPUR, near ALLAHABAD (
U.P).
The longitudinal
difference between
Mirzapur and GREENWICH is 5 hr 30 min.
As the standard meridian of India is towards the east of the
PRIME MERIDIAN, the standard time of India is 5 hrs 30 mins ahead of GMT.
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