· Equator is an imaginary line passing round the earth
midway between the north and south poles, dividing the earth into two equal halves.
· Latitude is the angular distance in degrees on the earth’s
surface measured north and south of the equator. The latitude of any point on
the earth is most precisely expressed in degrees, minutes and seconds.
· There are about 180 parallel latitudes. The distance
between any two parallel latitudes is always equal. One degree of latitude is
approximately equal to 111 km.
· All the parallel of latitude are not of equal length. The
circles become smaller towards the poles.
· Equator is at 0ºC is the most important latitude and is
the largest circle that can be drawn on the globe
· A meridian is an imaginary line extending from the north pole
to the south pole at right angles to the equator.
· Prime Meridian is the 0º meridian which passes through
Greenwich, a place near London. It is also known as the Greenwich meridian.
· Longitudes are equi-distant lines drawn east and west of
the Greenwich meridian. They denote the angular distances of a place due east
or west of the Greenwich meridian. There are 360 meridians of longitudes.
· One hour is equal to 15º of longitude
· Longitude is an important factor in determining the time
in all parts of the world. Local time of a place is calculated with respect to
the midday position of the sun at that place.
· Local time varies
from Greenwich time (London) at the rate of four minutes/ degree of longitude.
· Standard time is the uniform time fixed by each country
· Standard time in India is the local time of a place near
Allahabad at 82½ºE longitude.
· Greenwich Mean Time is the standard time of UK. It is
based on the local time of the meridian passing through Greenwich near London.
· If a person going east of Greenwich for 180º, he would
put his clock forward by 12 hours. At the same time if another person is going
to west of Greenwich for 180º, he would put his clock backward by 12 hours.
When they meet on the International Date Line, there would be one day’s difference
between them.
· Earth is divided into 23 full time zones and two half
time zones each having longitudinal width of 15º and 7½º respectively
· The International Date Line is situated at 180º meridian
from Greenwich. It runs down the mid Pacific Ocean, veering to keep all of the
islands in a group.
· When one crosses the International Date Line from east to
west the date is to be advanced by one day (loses on day). Similarly, when one
crosses the Date Line from west to east, the date is to be set back by one day.
· The International
Date Line (the meridian 180º) was chosen because it passes through the
mid-Pacific, where there are no land masses.
· It goes zig-zag in some places to avoid land and leaves
some island groups wholly on the same side of the line
· It deflects to the east of 180º the Bering Strait,
between Siberia and Alaska
· It deflects to the West of 180 º to leave the Hawaiian group
of islands on the East of the line
· It deflects again to the East, South of the equator to
avoid the Fiji and Tonga islands, on the same side as New Zealand. If the date
line is drawn exactly North and South, it will cut inhabited islands making
what is Tuesday to one man, a Wednesday his next door neighbour.
· A ship while crossing the Date Line eastwards gains a
day, while it loses a day crossing westwards.
· The local time of Arunachal Pradesh is two hours ahead of
that of Gujarat because Arunachal Pradesh is 30 º east of Gujarat.
· Russia, the largest country in the world, extends 165 º
from East to West. Therefore it is divided into eleven time zones, each differing
in one hour.
· The distance between any two meridians is not equal. They
get closer from the equator to poles
· Since earth rotates 15 º in one hour, there is a difference
of one hour in local time in every 15 º
· Sidereal day is the time between two observed passages of
a star over the same meridian of longitude.
· Sidereal day = 23 hrs.56 min.4.09 seconds
· Solar day is the time between two successive transits of
the sun over the same meridian.
· Mean solar day = 24 hrs.
KERALA PSC / PHYSICAL GEOGRAPHY / LOCATION OF PLACE AND
TIME ON THE EARTH’S SURFACE / NOTES
