Longitude and Latitude -UPSC Notes

Longitude and Latitude are geographical coordinates on the Earth that determine the location of any place on the Earth. The latitudes and longitudes are angles that uniquely define points on the Earth.

Both the Longitude and Latitude are measured in Degrees as they represent angular distances. Each degree is further divided into minutes (‘), i.e., (1 degree= 60 minutes), and each minute into 60 seconds (“), i.e., (1 minute=60 seconds).

Latitude

• Latitudes are angular distances of points on the surface of the Earth that are measured in degrees from the centre of the surface of the earth.
• Lines of latitude that encircle the Earth, running parallel to the equator, so they are also called parallels.

• There is a total latitude of 180 degrees. The distance between each degree of latitude is about sixty-nine miles, i.e., 110 kilometers.

Important lines of latitude (parallels of latitudes):

Apart from the equator, i.e., 0 degrees, the North Pole, i.e., 90 degrees North and the 90 degrees South, there are 4 important lines of latitudes.

• Tropic of cancer  (23 ½  North) in the Northern Hemisphere.
• Tropic of Capricorn (23 ½  South) in the Southern Hemisphere.
• Arctic Circle at 66 ½  North of the Equator.
• Antarctica circle 66 ½  South of the Equator.

Heat Zones of the Earth:

The mid-day sun is exactly overhead. The region that receives direct sun rays throughout the year and experiences maximum heat is called the Torrid Zone. It is a zone between the Tropic of Cancer and the Tropic of Capricorn.

The Frigid Zones are the coldest region of Earth and receive slanting rays of the sun as this region lies farthest from the Equator. This region lies between the Arctic Circle and the North Pole in the Northern Hemisphere and the Antarctic Circle and the South Pole in the Southern Hemisphere.

Longitude:

• These lines are semicircles, and the distance between them decreases slowly polewards until it becomes zero at the poles, where all meridians meet.
• It was difficult to number the meridians as all meridians are of equal length. Therefore, it was decided that the count should begin from the meridian, which passed through Greenwich, British Royal Observatory near London. The line is also called the prime meridian or 0° longitude.
• The Greenwich meridian passes through France, Spain, Algeria, Mali, Burkina Faso, Togo, Ghana and Antarctica.
• The longitude runs 180 degrees east and 180 degrees west. The longitude also defines Greenwich Mean Time.

Longitude and Time:

• The earth completes one revolution of 360° in a day (twenty-four Hrs); it passes through 15° in one hour or 1° in four minutes.
• The earth rotates from westward to eastward, so every 15° we go east, local time is advanced by 1 hour. Similarly, if we go west, local time is retarded by 1 hour.
• Thus, as we move eastward of Greenwich, we gain time, whereas we lose time as we move west of Greenwich Time.

The International Date Line:

• An imaginary line on Earth’s surface defining the boundary between one day and the next is known as the International Date Line (IDL).

• In 1884, the line passes through the mid-Pacific Ocean and roughly follows a 180° longitude north-south line on the Earth. The line is curved (zig zag) at some places to prevent confusion of day and date that are cut through by the meridian.
• It is located halfway around the world from the prime meridian, i.e., the 0 degrees longitude line in Greenwich.

Indian Standard Time:

In order to maintain uniformity of time as far as possible within the territorial limits of a nation, the time at the central meridian of the nation is taken as the Standard Meridian and its local time is taken as the standard time for the whole nation.

Countries with large eastward areas may choose more than one standard meridian to get more than one time zone, such as Canada, Russia and the United States of America (USA). There are a total of 24 major time zones in the world