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The opposite meridians of longitude form a Great circle because by each of them the world is divided into two equal parts 

The latitude of a place is the angular distance of the point north or south of the equator measured in degrees. The equator is taken as 0° latitude. Latitudes are measured from 0 ° to 90° N and 0° to 90° S. The distance from the equator to 90° N covers a distance of 1/4 of the circumference of the Earth or 140,000 km. One degree of latitude is equivalent to the length of about 111 km or 69 miles.

1. The length of the lines of latitudes decrease with distance from the equator. 

2. All lines of latitude are circles parallel to the equator.

Lines of longitude are lines which join all places having the same angular distance east or west of the Prime Meridian. All lines of longitude are semicircles of equal length. Lines of longitude are also called Meridians because all places along a lines of longitude experience mid-day at the same time.

Other meridians of longitude are the lines which join all places having the same angular distance, east or west, of the Prime Meridian.

The word ‘meridian’ means related to noon or 12 p.m. As every longitude receives the noon time or 12 p.m. at different intervals where the sun’s rays are exactly vertical over a particular longitude. On a particular longitude the noon-time is the same from north to south ; so a longitude is also called a Meridians of longitude.

Pole-Star is located vertically above the North pole .

24 time zones, has the world been divided.

The earth rotates on its axis from west to east, hence places in the east have their sun rise earlier than places in the west. Now if a man travels round the world from east to west, for every degree of longitude covered; he will have to set back his watch by four minutes. Thus after covering 360°when he returns to the place from where he started he will have to set back his watch 360 x 4 / 60 = 24 hrs. Thus he will appear to have lost a day. When Francis Drake returned to England after circumnavigating the globe, he thought it was Saturday, where as actually it was Sunday. The reason was that he had traveled from east to west, and had under calculated a day. On the other hand if a man travels from west to east, for every degree of longitude covered he will put forward his watch by four minutes and for 360° he will forward it 24 hrs. When he returns to the place from where he started he will appear to have gained a day. When Cap. Basil Hailed reached Manila after circumnavigating the globe, he thought it was Monday; where as actually it was Sunday. The reason was that he had traveled from west to east and had over calculated a day.

90° N and 90° S.

0° is the latitude of equator .

(a) Equator is the starting line for all the parallels. It is zero degree parallel. 

(b) Tropic of Cancer – 23 1/2° North parallel. 

(c) Tropic of Capricorn – 23 1/2° South parallel. 

(d) Arctic circle – 66 1/2° North parallel. 

(e) Antarctic circle – 66 1/2° South parallel.

Latitude is the angular distance from the plane of the equator. All of surfaces (planes) or circles make a maximum angle of 90° from the plane of the equator. Therefore, maximum latitude is 90° N in the Northern Hemisphere and 98° Southern Hemisphere.

Equator is the longest line of latitude.

1. The distance between two consecutive longitude decreases gradually with distance from the equator. 

2. All lines of longitude are semicircles of equal length.

23 1/2° North.

(a) The time and date changes as we cross the International Date Line i.e. the navigators or pilots have to loose one day while crossing westwards and gain one day while crossing eastwards i.e. When one travels from Tokyo to San Francisco on Monday, he will reach San Francisco on Sunday.

(b) The International Date Line is not a straight line but have some deviations in order to adjust with the pattern of the landforms and some islands to decide for the time and date of these places and regions. 

(c) If we are moving from Hawaii Islands towards Shanghai on Tuesday, we will reach there on Wednesday or Thursday probably, but if we are going eastwards from Shangai to Hawaii islands on Tuesday. We may reach there either on Tuesday or Monday.

Indian Standard Time is based on 82 1/2° E longitude. So if the time in India is 12 noon, so it will be 6.30 A.M. in England or GMT. The time difference between 0° and 82 1/2° E will be 82.5 × 4 – 330 minutes or 330 ÷ 60 = 5 1/2 hours. So there is difference of 5 1/2 hours between India and England, as England lies in the west, so the time will be 5 1/2 hours less than India.

An Example: 

A cricket match was to be held at Birmingham at 9 a.m. local time. The position of Birmingham is 5° W. Calculate the time the viewers have to tune their television in Sydney 151°E. Answer: The local time at Birmingham is 9 am. The location of Birmingham is 5° W of Prime Meridian. The GMT would be 9:20 a.m. [9.00hrs + (5° × 4min) = 9.00hrs + 20 min = 9.20 a.m. Sydney is located at 151 °E of Prime Meridian At any point of time Sydney would be 151 × 4 = 604 min = 10 hrs 4 min ahead of GMT (Sydney is to the East of the Prime Meridian so local time would be ahead of GMT) When it is 9:20 a.m. GMT the local time at Sydney would be (9:20 + 10:04) 19:24 hrs or 7:24 p.m. in order to watch the Brimingham match at Sydney the viewers would have to tune their televisions at 7:24 p.m. local time.

A longitude is the angular distance of a place east or we§t of the Prime Meridian or 0° longitude. The lines of longitude are the great semi-circles joining North pole and South pole and are equal in length. These are 0° – 180°E and 0° – 180°W longitudes or total 360°. As the earth takes 24 hours to make a complete rotation along its axis crossing 360° lines of longitude, so earth takes nearly 4 minutes to move one degree (1 °) longitude or 111 km length or distance. There is difference of time of one hour between 15° interval of longitudes. According to the clock-time, EGA stands for East-Gain-Add and WLS means West Lose Subtract. In other words for each 10 longitude towards east 4 minutes are to be added and towards west for each 1° longitude 4 minutes are to be subtracted.

There is a close relation between longitude and time. The Earth makes one complete rotation of 360 degrees in 24 hours. It passes through 15 degrees is one hour or one degree in four minutes. Thus, there is a difference of 4 minutes of time for one degree of longitude. As the Earth moves from West to East, the places East of Greenwich gain time whereas the places West of Greenwich loose time.

it is because of change in longitude at several places.

It marks the Southern limit of tropical zone.

0° meridian.

The Prime (or First) Meridian is the meridian from which longitude is measured. It is numbered. 0° longitude. It is the meridian which passes through Greenwich (near London). Thus the Prime Meridian is also called Greenwich line.

Greenwich Meridian is called the ‘Prime Meridian’ or the 0° longitude. The time is calculated with respect to this Meridian. So it is the basic Meridian and time is written as G.M.T. (Greenwich Meridian Time) The earth takes 4 minutes for moving 1° distance.

The circumference of the Earth is approximately 40,000 km. It covers ah angle of 360 degrees. The distance between two consecutive parallels of latitude is everywhere the same. This is because lines of latitude are parallel lines. Therefore one degree of latitude. = 40,000/360 = 111km (approximately.) On the other hand, the distance between two consecutive meridians of longitude is 111 km only at the equator and gradually decreases with distance from the equator. This is because the meridians of longitude converge at the two poles.

The face of the earth is divided into various parallel circles with respect to the equator on both sides at different angular distances. These lines are veiy important to decide the climate and temperature range of any place or region as the temperature goes on decreasing from the equator to polewards.

The Temperature goes on decreasing from the equator towards the poles. So the latitudinal zones are the actual heat zones of the earth, namely tropical, temperate and polar zones.

Local time may differ from place to place. Therefore, it is only a theoretic reality. On the other hand, standard time is the same for a particular country. It is a practical necessity for the sake of uniformity of time.

The International Date Line passes through the Pacific ocean where there are no land masses. It follows 180° meridian for most of its distance. The date line is zig-zag in some places to avoid the confusion of time on the same island. It avoids some islands and deviates from 180°. In Northern Hemisphere, it bends to the West of 180° while in the Southern Hemisphere it bends Eastwards.

The time difference between the required place and New Delhi is 6 + 9 = 15 hours, so the time in minutes =15 × 60 = 900 minutes So the longitudinal difference = 900/4 = 225°. So the place will be in the west 225° – 77° = 148° W.

The longitudinal difference between Durban and New York is 30° + 75°= 105°, so the time will be 105 x 4 = 420 minutes ahead from New York. There is the difference of 420 minutes or 7 hours, or 2 p.m.

Equator is the longest parallel on the Earth. All other parallels become shorter polewards due to spherical shape of the Earth. So the meridians near the poles have a narrow space. One degree of longitude is the longest at the equator (111 km) at 45° latitude it is 79 km, at 60° latitude it is 55 km and at poles, it is zero km.

Longitude is the distance of a place east and west of the Prime Meridian along a parallel of latitude. This distance is measured in degrees. When we say that the Longitude of Delhi is 77° East, we mean that Delhi lies East of the Prime Meridian and its distance from the Prime Meridian is 77° The Longitude of a place can be determined by comparing its Local Time with Greenwich Time. Greenwich Time can be known either by radio or by means of a watch which keeps Greenwich Time. Captains of ships generally use a Chronometer for this purpose. A Chronometer is a time piece which keeps accurate time and which is not affected by change in temperature. Now suppose that when it is 2 p.m. at Greenwich, another place shows 5 p.m. The difference between the times of two places is 3 hours, that is 180 minutes. Thus the place is =180 / 4 = 45° away from the Prime Meridian and since its time is ahead of Greenwich. Its longitude will be 45° East.

As the Earth rotates from west to east about its own axis, the zone of illumination moves slowly towards the west. This accounts for variation in the time of Sunrise and Sunset at different places on the Earth. The Earth takes 24 hours to complete one rotation. This means that 360 degrees of longitude are covered in a period of 24 hours. This gives rise to a time difference of [24 × 60/360] or 4 minutes for 1° of longitude. The time difference is to be added in case of places to the east of a point. In case of places to the west, the time difference is to be subtracted. It is possible to calculate the time at a given place A from the time recorded at B and the longitude difference between stations A and B.

The Tropical zone gets vertical rays of the sun, while temperate and polar zones receive slanting rays of the sun.

The thermal zones of the earth are Tropical, Temperate and Polar zones.

The longitudes in the Eastern Hemisphere are marked E while the longitudes in the Western Hemisphere are marked W.

The intersection of latitude and longitude points out the exact position of a place on the earth’s surface. For example London is situated at 51°30’N (latitude) and 0.5 W (longitude). With the help of these intersecting lines, it is convenient to locate the position of London on the map. Actually, latitude and longitude are both imaginary lines drawn on a map or a globe in order to locate the position of a place or a region on the earth’s surface.

A globe is a man-made spherical model of the earth. A globe is very useful model to display the actual shape of the earth with its tilted axis ; The rotation and revolution of the earth can be very clearly shown by it along with the continents and oceans.

The latitudes in Northern Hemisphere are marked N while the latitude in Southern Hemisphere marked S.

4 minutes per degree.

Longitudinal value of Indian Standard Meridian is 82 1/2° E. It passes midway through India nearly along the city of Allahabad

Large countries like Russia, Canada and the United States have vast longitudinal extent. They do not have a single Standard Time for the whole Country. They have many time zones, with each time zone covering about 15° of longitude. The erstwhile Soviet Union had 11 times zones to cover 165° of longitudinal extent. Canada and the United States have five time zones extending from the Atlantic coast of the Pacific coast. There is time difference of five hours between the two coasts.

The temperature decreases northwards and southwards from the equator. The region within 23 1/2° N and 23 1/2° S will get tropical climate with ample temperature and rainfall. On the other hand the regions between 23 1/2° N – 66 1/2° N and 23 1/2° S – 66 1/2° S will get temperate climate, while the regions known as Arctic and Antarctic circles get very cold polar climate as Tundra region.

The network of the latitudes and the longitudes is known as a geographical grid.

The total circumference of a circle is 360° and the distance between the Equator and the North Pole is one-fourth of the circumference i.e. 90°. So we have 90 latitudes towards north and 90 towards south, which are denoted as 90° N and 90° S respectively.

The Great Circle Routes follow the great circles i. e. the perimeters of the earth, which cover the shortest distances between any two places in spite of the zigzag routes along the surface of earth. These circles are beneficial for following the shortest distances between any two places and help in saving the time. i. e. the shortest routes are covered in minimum time span.

Eratosthenes, the Greek philosopher, first time devised the lines of latitude and longitude.

IDL means the International Date Line, which is along 180° E & W. The date or day changes while crossing this line i.e. while there is Monday in the Eastern Hemisphere i.e. 0° – 180°E, there will be Sunday in the Western Hemisphere i. e. 0° – 180° W.