Everyone of us will have a doubt as to how can we locate points on earth's surface. Locating positions on earth can be done by using the latitudes and longitudes of earth. Earth's surface is divided into imaginary lines for
locating points or positions. The lines drawn parallel to the equator are called Latitudes (are also called Parallels) and the lines that run perpendicular to
the equator are called Longitudes (are also called Meridians). Latitudes are 180 in number and longitudes are 360 in number.
The shape of the earth is called Oblate spheroid or Distorted sphere. But on globe, we ignore the these distortions and the relief of the earth's surface.
Rotation of the earth on its own axis causes day and nights and Revolution of earth around Sun causes seasons.
Due to inclined axis of Earth around which
it rotates, the day and night durations are not equal. They also vary from one place to the other place. The angle of inclination of earth with orbital plane
is 23.50. That is, the axis of the earth is inclined at an angle of 66.50 with reference to the orbital plain around the sun.
Locating Positions on Earth
- Latitudes are parallel to each other. That is they are at equidistant to each other. The distance between two latitudes, which are adjascent
to each other, is equal to 110 km. Pole is represented just by a point.
Meridians connect the poles (converge at the poles) from North to South.
The distance between two longitudes, which are adjascent to each other, decreases from Equator to poles. At Equator, they are at distance of 111 km.
- On a given Latitude, all the Longitudes are equally spaced. All the latitude and longitude lines intersect at 900 at any point on earth.
This arrangement of network of longitude and latitude lines is known as "Graticule".
- Then, how would we locate a place on the surface of the earth, let us see. Any place or point or position on the Earth can be found out using the
latitude-longitude coordinates given in Degrees, Minutes and Seconds. 1 Degree is divided into 60 Minutes of Arc. 1 Minute of Arc is
further divided into 60 Seconds of Arc.
For identifying the position on earth's surface, Latitude degrees are calculated from the Equator and Longitude degrees are calculated from
the Standard Meridian located at Greenwich near London. The maximum value of Latitude degrees is 90° N or 90° S and the maximum
value of Longitude degrees is 180° E or 180° W.
For example, the mainland India is located between 8°4' and 37°6' North Latitudes from the Equator and between 68°7' and 97°25' East Longitudes
from the Standard Meridian.
- International Date Line longitude is taken roughly around the 1800 Meridian line. It is selected so that International Date Line
passes mostly through the waters and not through the countries.
The date line is somewhat deviated at some places so as to cover the political boundaries of
Longitude and Time Calculation
Let us see how to calculate local time using longitude lines
- Meridians control the time as Earth rotates from West and East. Then, how to calculate time difference between two longitudes? Let us see.
3600 rotation of earth is equivalent to 24 hours.
So, 15 degrees is equivalent to 1 hour or 60 minutes and hence, 1 degree is equal to 4 minutes..
As one Meridian represents 1 degree, each Meridian is separated by the next Meridian by 4 minutes of time.
- Indian Standard Time (IST) is based on the Meridian passing through 82 1/20 East. It is Passing through Mirzapur and Kakinada.
The Standard Meridian passing through Greenwich is taken as the Standard for Time, called Greenwich Mean Time (GMT).
In 1884, at International Meridian Conference in Washington, Greenwich Meridian was taken as international standard for zero degree. IST of India is
5 1/2 hours ahead of GMT.
A country's time zone and local time will be calculated based on how many degrees or longitudes distance it is having
from the GMT.
- Some of the countries having different time zones are Canada, US, Russia, Australia, etc. Generally, for each 150 Meridian, they will have one
Equinox - It is the moment where the center of the Sun is right above the Equator. This situation arises twice in a year, on 21st March and on 23rd
Solstice - It is the moment where the Sun appears to be at maximum deviation either northerly or southerly from the Equator. This situation arises twice
in a year, 21st June and 22nd December.