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Literary meaning of the word ‘Geography’ is to know the details of some location, distribution of facts, populations etc. Details of some location from the climatic aspect and time cannot be explained if we do not take help of latitudinal and longitudinal measures of particular place. In other words, distance from Equator is most important fact for some place while seeking its details.
Earth continues two motions all the time i.e. rotation and revolution. The imaginary line drawn on the earth which divides it into two parts known as northern and southern hemispheres is known as Equator.
Physical location, climate, vegetation etc. may be known more thoroughly depending upon the factual distance of some region from the Equator. The cartography of longitudes has made things more easy for marine explorers during their oceanic navigation.
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Various experiments have been carried out to settle longitudinal cartography:
Amerigo Vespucci faced a lot of problems when he tried to measure expansion of Earth, east to west i.e. horizontally on 23rd August 1499. He sought help of Almanac measurements to find relation with various other celestial bodies and concluded that position of Moon is at 3 1/2° East of Mars.
This conclusion of his has made basis for drawing longitudes. His experimentation and results however could not find favour with various thinkers of his times. It did not suit according to Almanac Calender even as there was no stable platform on which his theory could be raised.
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Galileo Galilei gave a theory in 1612 A.D. that orbits of Moon and Jupiter may be used as clock. He proved it by experimentation but in 18th century a lot of incidents happened on earth in which exact location in the oceans could not be found. In this situation, the British Government set up a Board of Longitudes in 1714 A.D. and motivated experimentation and research on the issue by announcing various prizes for it.
John Harrison, an English clockmaker brought out a marine Chronometer which could study longitudinal positions in Oceans. This instrument however, was very costly and beyond reach of many, financially.
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Therefore Lunar Distance Method of Amerigo Vespucci remained popular for many decades. It was in 20th century, wireless telegraph went more popular than lunar distance method. Starting point for latitudes was equator uncontestedly but emergence of longitudes saw various experiments.
Hipparcus brought out a grid of latitudes and longitudes in 300 B.C. and various maps were drawn with the help of local time and absolute time. He contributed in setting up of starting longitude. His measurements were however more clarified 75 years later i.e. in 225 B.C., Eratosthenes, a Greek Mathematician and Space scientist, measured circumference of Earth and prepared maps of the world.
Another explorer Al-Birunie gave theory that Earth rotates round its axis which results into direct relation between longitudes and time. After all this experimentation, the International Community proposed Greenwich longitude as starting longitude in 1884 A.D. and it was accepted world over.
1. Latitudes or Parallels:
The angular distance of any place falling in north or south of Equator is known as its latitude. These latitudes or parallels are measured in degrees, minutes and seconds. Geometrically, a circle is measured at 360 degrees (°) and same is for equator. Each degree is divide in 60 minutes (‘) and each minute is further divided in 60 seconds (“).
An imaginary straight line joining North and South poles when intersects Equator, it divides circle in four parts, each of 90°. Hence earth is divided in 90° parallels in Northern Hemisphere and 90° parallels in Southern Hemisphere. The places in the north of Equator are represented with latitudinal degrees followed by ‘N’ and those in south, with latitudinal degree, followed by ‘S’ while equator remains 0°. As it is very clear that a place situated at 1° angle from Equator shall be at 1° parallel, in kilometers each degree in 111 kilometers away from the other.
Latitudinal lines are those imaginary lines which join all the places on globe which are at same angular distance from equator. Equator is known as ‘Great Circle’ also which divides the earth in two equal parts. Parallels or Latitudes are not straight lines but circular lines drawn parallel to equator horizontally. These circles have same centre i.e. axis and 90° N and 90° S are more points.
Some important latitudes or parallels are as under:-
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(i) Equator – 0°
(ii) Tropic of Cancer – 23 1/2°N
(iii) Tropic of Capricorn – 23 1/2°S
(iv) Arctic Circle – 66 1/2°N
(v) Antarctic Circle – 66 1/2°S
(vi) North Pole – 90°N
(vii) South Pole – 90°S
Latitudes or parallels have very important and close relation with sunlight, revolution, tilt at 23 1/2° angle and so on. Sun shines straight over Tropic of Cancer (23 1/2°N) on 21st June and over Tropic of Capricorn (23 1/2°S) on 22nd December. It results in making June 21 the longest day in Northern Hemisphere while December 22 the longest day in Southern Hemisphere.
Arctic Circle (66 1/2°N) region does not experience high temperature in June while sunrays reach across North Pole in this period of the yearly voyage. Same way in December when Southern Hemisphere is tilted towards Sun, the sunrays cross South Pole to reach 66 1/2°S latitude i.e. Antarctic Circle. Hence Polar Regions have continuous days and nights whole the year long.
The tilts of Earth and approach of sunrays allows us to divide the Earth into various temperature zones also. Regions lying 0° to 23 1/2°N and 0° to 23 1/2°S are known as Tropical regions while regions lying between 23 1/2 °N to 66 1/2 °N and 23 1/2 °S to 66 1/2 °S are known as Temperate regions. Regions falling above 66 1/2°N to North Pole or 66 1/2°S to South Pole, are known as Polar Regions or Polar Regions or Frigid Zones.
Distance from Equator i.e. latitudinal situation and distance above sea level are two major factors which have their effect over climate of some place. Any place situated near the Equator shall remain hot as such region shall remain under direct sunlight whole the yearlong whereas places near poles which never receive straight sunrays shall remain cold in control to equatorial regions.
Measuring Latitudinal Position of Some Place:
It is necessary to know declination of the sun if we want to know latitudinal positioning. Zenith is a place exactly overhead in space. The zenith distance and declination of sun or angular distance from Equator at a particular place and time, if calculated, tells us our latitudinal position. When a person moves from a place, his/her zenith distance also changes and that changes latitudinal positioning.
North Pole lies exactly beneath North Star which we may find with the help of pointers of Great Bear. At night, angular distance from North Star can conclude of our latitudinal position. Chandigarh is at 30°.42’N latitude.
2. Longitudes or Meridians:
Geographical location is not very feasible to find with a single geographical factor. Location and time surely need latitudinal measurement to conclude measurement while what needs more or in addition to it, is longitudinal position. More precisely we can say that location and time may be found out not only by knowing north-south position but east-west position also. Longitudes are those imaginary lines drawn on a globe which join North and South poles.
These lines are also circular actually, intersecting at North and South poles but at first sight these look like arcs. We take 0° longitude as Prime Meridian, which passes through a place known as Greenwich near London. There are 180° longitudes towards east of Prime Meridian and same number is there towards west of Prime Meridian. 180° Meridian which falls exactly opposite to Prime Meridian is again a common Meridian from east or west and technically known as International Date Line.
The full circle of 0° & 180° longitudes divides the Earth in two parts known as Eastern Hemisphere and Western Hemisphere respectively. Distance of a place east or west of Prime Meridian is measured as an angle and this angular distance is called the longitude of that particular place.
India is situated in Eastern Hemisphere. Longitudes are always of equal size and are around 69 miles away from each other at the Equator. Longitudes or Meridians are also measured in degrees, minutes and seconds.
Find Out what is Geoid?
In simple language the Zenith refers to an imaginary point directly “above” a particular location on the imaginary celestial sphere. The Zenith is the highest point on the celestial’s sphere.
The North Pole also known as the Geographic North Pole is defined as the point in the Northern Hemisphere where the Earth’s axis of rotation meets its surface. North Pole is the northern most point on the Earth, lying diametrically opposite the south pole. It is also called true North.
A Pole star is a visible star, preferably a prominent one, that is approximately aligns with the Earth’s axis of rotation, that is a star whose apparent position is close to one of the celestial poles, and which lies approximately directly overhead when viewed from the Earth’s North Pole or South Pole and Geoid is the shape that the surface of the oceans would take under the influence of Earth’s gravitation and rotation alone, in the absence of other influences such as winds and tides.
All points on the Geoid have the same gravity, potential energy. The force of gravity acts everywhere perpendicular to the Geoid, meaning that plumb lines points perpendicular in water levels parallel to the Geoid.
Grid System of Latitudes and Longitudes:
As we draw longitudes and latitudes on a globe, it looks like a full-fledged net or grid, therefore drawing of longitudes and latitudes is known as Grid System. If we are to find location of some place on globe or map and we have its longitudinal and latitudinal position.
For example Patiala (Punjab) is located at 30°.23′ North latitude and 76°.21′ East longitude. While trying to find it on a map, it shall lie at the place where these two latitudinal and longitudinal lines intersect one another.
Longitude and Time:
Longitudes help us calculate local time of a place which in turn helps us about timing of sun rise and sun set. Greenwich Meridian is first longitude and it is presumed universally that when sun is shining above this longitude, that is to be called noon 12:00 GMT (Greenwich Mean Time).
The Earth rotates round its axis one full circle in 24 hours means 360° cross in that span of a day. On calculating it further, we conclude that 15 degrees face sun in an hour and one degree in 4 minutes. As we proceed eastwards from Greenwich Meridian, we add up time at rate of 4 minutes per degree while proceeding westwards we have to deduct time at same rate. India and U.S. have a difference of 9 hours 30 minutes as India falls in Eastern Hemisphere while U.S. falls in Western Hemisphere.
In other words, when Greenwich has noon, means when clocks strike 12 at Greenwich, clocks at 15°E shall strike 1 p.m. while clocks at 15°W shall strike 11 a.m. At the same rate clocks at places 30°E shall strike 2 p.m. while at 30°W shall strike 10 a.m.
It shows that if we know longitudinal location of a place, we can find time easily. For example; India has set its standard time at 82 1/2°E longitude which passes near Allahabad.
The time at Allahabad or 82 1/2°E shall be calculated like this:
Greenwich longitude = 0°
Allahabad longitude = 82°.30′
Difference of longitudes = 82°.30′ – 0° = 82°.30′
Difference of time = 82.5 x 4 minutes = 330 minutes or 5 hours 30 minutes
As Allahabad falls in east of Greenwich, 5.30 hours shall be added to the time at Greenwich or popularly we say that time in India is +5.30 hours to Greenwich Time.
Indian Standard Time:
Each place has its own local time which is due to longitudinal difference of each place. Recognition of local time of each place brings variation of time to the extent that it cannot be cured for setting time for various systems such as transport, offices and so on. To overcome this problem, each nation has set its time according to some standard longitude. Such a time is known as ‘standard time’ which is based upon some Central Meridian of each nation.
India has set 82 1/2°E longitude as its Standard Meridian which passes close to Allahabad. This longitude divides India in two parts vertically. Standard time for whole the world is calculated from Greenwich Meridian and time is known as Greenwich Mean Time i.e. G.M.T. whereas that of India, it is known as Indian Standard Time i.e. IST.
Time difference of local times of Dwarka (Gujarat) in west of India and Dibrugarh (Assam) in east is of 1 hour and 45 minutes. Farthest extent of India towards East lies in Andaman and Nicobar islands.
Some big nations i.e. with broad East-West extent, have more than one standard times. Russia has 11 standard times while U.S.A. and Canada have 9 and 6 respectively and as many time zones of their own.
International Date-Line:
Emergence of longitudes and distribution of time on the Earth according to longitudes left one problem unsolved that at which longitude, date shall change. To table with the issue, International Meridian Conference was held at Washington in 1884 A.D. and 180° longitude was finalised as International Date Line (IDL) which passes through Pacific Ocean and separates two dates.
Tango and American Samoa are two islands places located quite close in Pacific Ocean but Tango lies in Eastern Hemisphere and American Samoa in Western Hemisphere and therefore there is a difference of full one day in dates of these two islands.
Fiji lies in the East of Tango and its time trails for an hour as compared to Tango. On the other hand Hawaii islands are in the west of Samoa and its time in one hour ahead of Samoa. There are many island nations or places in Pacific which have to tinker with time.
We divide the world in 24 standard time zones. Each time zone contains 15 Meridians. As 180° Meridian of International Date Line falls exactly opposite to Greenwich Meridian (0°), the time difference between these two longitudes is of 12 hours. Immediately to the left of the International Date Line, the date is always one day ahead of the date (or day) to the right of the International Date Line in Western Hemisphere.
What is Globe Positioning System (GPS)?
In simple words, date changes at International Date Line. As we proceed towards east, a day is deducted but as we travel towards west, a day is added. For example if a traveller crosses International Date Line while travelling towards east, a day needs to be deducted but when that traveller crosses back International Date Line towards west, a day needs to be added.
International Date Line passes through Pacific Ocean that saves many people from changing calendars frequently because had it been passing through land area, people would have faced trouble of frequent change in calendars.