Locating Places on the Surface of the Earth

(Any location on Earth is described by two numbers i.e. its latitude and its longitude)

We know earlier that our earth spins continuously on an imaginary axis which passes through the center of the earth. Astronomers and geographers considered the Northern tip of the axis as North Pole and the Southern tip of the axis as South Pole. But another thing, cartographers considered the largest possible circle that can be drawn on a globe or our earth is Equator. It divides the globe into two equal halves. The northern half is known as Northern hemisphere and the southern half is Southern hemisphere.

Latitudes

Parallels of Latitude

Since the distance from the equator to either of the poles is 1/4th of a circle round the earth, it will measure ¼ of 360 degree i.e.90 degree. Thus 90 degree North latitude marks the North Pole and the 90 degree South latitude marks the South Pole. Parallel to the equator one set of imaginary lines are drawn which encircle the earth and run in east west directions. These are called latitudes. Since all these lines are parallel to the equator as well as one another, they are called parallels of latitudes.

Latitude is the angular distance of a place from the equator, lying either in the north or in the south directions. It is measured in degrees from the equator toward either pole. One degree (0) is divide into sixty equal parts and each unit is called a minute (’). A minute is further divided into sixty equal parts and each unit is called a second (”). From the equator to the poles, parallels of latitudes become smaller. It becomes a point at the pole. Generally, there are 90 latitudes taken at an interval of 1 degree in the northern and southern direction of the equator. The value of the equator is zero. All points north of the equator are called ‘north latitudes’ and all points south of the equator are called south latitudes. Therefore, the value of each latitude is, followed by letters ‘N’ or ‘S’.

Important latitudes

Heat Zones & Imp. Latitudes

Besides the equator (0 degree), the North Pole (90 degree N), the South Pole (90 degree S), geographers have imagined four important parallels of latitude. They are: (i) the tropic of Cancer (23 degree 30 minute N), (ii) the tropic of Capricorn (23 degree 30 minute S), (iii) the Arctic Circle (66 degree 30 minute N), (iv) the Antarctic Circle (66 degree 30 minute S).

Heat Zones of the Earth

Torrid Zone: The mid-day sun is exactly overhead at least once a year on all latitudes in between the Tropic of Cancer and the Tropic of Capricorn. Therefore, this area gets maximum heat and is called the Torrid Zone. On 21st June the Sun is directly over the Tropic of cancer. On 22nd Dec the Sun is directly over the Tropic of Capricorn. These two latitudes form the outer limit of the Torrid Zone. It is the hottest part of the world. Most of the deserts are located here.

Temperate Zone: The midday sun never shines overhead on any latitude beyond the Tropic of Cancer and the Tropic of Capricorn. The angle of the sun’s rays goes on decreasing towards the poles. The areas bounded by the tropic of cancer and the Arctic Circle in the Northern hemisphere and the Tropic of Capricorn and the Antarctic Circle in the southern hemisphere, have moderate temperature i.e. neither very hot nor very cold. So this is Temperate Zone.

Frigid Zone: Areas lying between the Arctic Circle and the North Pole in the Northern Hemisphere and the Antarctic Circle and the South Pole in the Southern Hemisphere, are very cold. It is because the sun does not rise much above the Horizon. Therefore its rays are always slanting. So this is Frigid Zone. 

Longitudes

Meridians of longtudes

A set of imaginary lines which divide the earth into eastern hemisphere and western hemisphere run over the earth in north south directions are called “meridians of longitudes”. These lines are not parallel to one another. They all converge at poles. The distances between them are measured in ‘degrees of longitude’. They form semi-circles. They are also drawn at an interval of 1 degree. These meridians of longitude and parallels of latitude form a network which is called grid. If a pilot or a ship's captain wants to specify a position on a map, these are the "coordinates" they would use. Even people who are in the defense sector or intelligence use these meridians of longitude and parallels of latitude as "coordinates". Unlike the parallels of latitudes, the meridians of longitudes are equal in length. As one go from the equator to the poles the distance between two meridians decreases.

Prime Meridian

In order to avoid confusion, there was an agreement world over that the longitude passing through Greenwich Observatory near the city of London will be considered as the Prime Meridian. Located at the eastern edge of London, the British capital, the observatory is now a public museum and a brass band stretching across its yard marks the "prime meridian." Tourists and local people often get photographed as they straddle it i.e. one foot in the eastern hemisphere of the Earth, the other in the western hemisphere. On the opposite side of the Earth at 180 degree longitude lies an imaginary line called the International Date Line. It is considered to be 0 degree Longitude and from it we count 180 degree eastward as well as 180 degree westward. It is interesting that 180 degree east and 180 degree west meridians are the same line in the middle of the Pacific Ocean. To avoid the confusion letters ‘E’ and ‘W’ are written with the values of meridians for the eastern hemisphere and western hemisphere respectively.

Time Zones

Time Zones of the World

The earth takes about 24 hours to complete a rotation. This period of rotation is known as the earth-day. This means in 24 hours the earth completes 360 degree. Therefore, it takes about one hour to complete each 15 degree or 4 minutes for each degree. Accordingly, the earth has been divided into 24 time zones of one hour each. As the earth rotates from west to east, day starts at different times in different places. When we are marking time world-wide, not tied to our locality it is Coordinated Universal Time (UTC), which can be defined as the local time in Greenwich, England, at the zero meridian. Places east of the Greenwich meridian experience sunrise earlier than the place lying west of the prime meridian. All the places situated along the same meridian will have the same sunrise hence same local time.

An interesting story of America

In the middle of the 19th century, each community across the US defined its own local time, by which the Sun, on the average, reached the farthest point from the horizon (for that day) at 12’ O clock. However, travelers crossing the US by train had to re-adjust their watches at every city, and long distance telegraph operators had to coordinate their times. This confusion led railroad companies to adopt time zones, broad strips (about 15° wide) which observed the same local time, differing by 1 hour from neighboring zones. Then the US adopted the system. Now, the continental US has 4 main time zones. They are eastern, central, mountain and western, plus several more for Alaska, the Aleut islands and Hawaii. Canadian provinces east of Maine observe Atlantic time. One may find those zones outlined on the map giving area codes. Other countries of the world have their own time zones; for example Russia has 11 standard times. Only Saudi Arabia uses local times, because of religious considerations.

International date Line

International date Line

As we know the opposite side of 0 degree latitude is the International Date Line, it passes through the mid-Pacific Ocean and roughly follows a 180 degrees longitude north-south line on the Earth. It is established in 1884. It is located halfway round the world from the prime meridian. It serves as a “line of demarcation” i.e. separating two consecutive calendar dates. Despite its name, the International Date Line has no legal international status and countries are free to choose the dates that they observe. It is not a perfectly straight line and has been moved slightly over the years to accommodate needs (or requests) of varied countries in the Pacific Ocean. Thus, the date line generally runs from north pole to south pole, it zigzags around political borders such as eastern Russia and Alaska’s Aleutian Islands. Immediately to the left of the International Date Line in the eastern Hemisphere, the date is always one day ahead of the date immediately to the right of the International Date Line in the Western Hemisphere. So, travel east across the International Date Line results in a day, or 24 hours, being subtracted. Travel west across the International Date Line results in a day being added.

Indian Standard Time

IST

In India the longitudinal span is from 68 degree 7 minute to 97 degree 25 minute E. Therefore, it was felt necessary to adopt the local time of central meridian of our country as the standard time for the country as a whole. In India 82 degree 30 minute E has been considered for this purpose. It is called the standard meridian. This is known as Indian Standard Time (IST). The Greenwich Mean Time is 5 hours and 30 minutes behind the Indian standard time.  India Standard Time is a half-hour time zone. Its local time differs by 30 minutes instead of the normal whole hour. This time zone is often called Indian Time. In global context Greenwich (0 degree) time is followed which is called the Greenwich Mean Time (GMT).