Parallels and Meridians for Using Navigation – Latitude and Longitude
These are sets of lines used to find the location of a place on earth. Latitude runs from east to west; while longitude runs from the north to the south of the earth. The lines are imaginary in nature. But they are normally drawn on maps as well as on the globe to show the direction of a place.
How to Draw the Earth Grid
There are two points of reference on earth; which help in drawing the grid: North Pole and South Pole. The points of reference are usually considered to be the points; at which the earth’s axis meets the earth’s surface. An east-west line; usually referred to as the Equator is drawn halfway between the poles. Thus dividing the earth into two equal parts; which are later referred to as hemispheres. Hence the North and South hemispheres in respective of the North Pole and South Pole.
Latitudes are drawn east-west just like the equator and they run parallels to it. In the earth’s grid, there are 89 latitudes on the northern hemisphere and 89 in the southern. The 90th latitude is represented by the North and South Pole meeting point.
Since they are circular in nature and the earth is a globe; the further the lines are from the equator, the shorter they become in nature.
The other set of lines
Longitudes are drawn from one pole to the other and run from north-south and don’t go around the earth. A longitude has been chosen by international agreement as the base line or zero point. This line passes through Greenwich. England; and thus referred to as the Greenwich Meridian or Greenwich base line. There are 180 longitudes and unlike the latitudes, these lines are all equal in length.
The zero line, just as the equator divides the earth into two equal hemispheres, the Eastern and Western hemispheres, according to the direction that they lines lie from the Greenwich base line, east and west respectively.
Parallels and meridians
All east-west lines (latitudes) are equidistant from each other. This interprets that they are all parallels to the equator as well as to each other; hence they are commonly referred to as Parallels.
The north-south lines (longitudes) are also referred to as meridians. The zero meridian or Greenwich base line is called the Prime Meridian. Each meridian usually goes halfway around the earth and from the North Pole to the South Pole meaning that each meridian has a twin on the other side of the earth. Because of this, their twin partners enable them to form circles that divide the earth into hemispheres. These circles are; hence referred to as the great circle. The equator too is a great circle.
Finding Latitude and Longitude
When navigating in a ship or airplane, you can determine the latitude of your position by using a special instrument called the sextant. The instruments enables one to measure the altitude; (height above sea level or angle above the horizon); of the sun as the earth orbits and then examining the tables indicated by the instrument. For instance, if you are navigating on noon of December 21st; the sun will be directly overhead.
This means that on that day the sun is above the Tropic of Capricorn, so your latitude would be 23.5 degrees south. Remember that the earth orbits at an even pace of 15 degrees per hour. Thus if the sun is above longitude of 0 degrees at noon, a hour later it will be at 15 degrees west. At night you can use the stars to calculate latitude.
For longitudes, it is a bit difficult to determine them because this instrument together with the almanac does not yield enough data. Therefore the best you can do to determine them is to know the exact time of the observation. Basically you will need a clock. Special clocks have been designed to enable navigators determine longitude correctly because they compare local time and Greenwich Mean Time (GMT).
Every 15 degrees west of the prime meridian will mean that local time will be one hour behind GMT and 15 degrees movement to the east will mean that local time will be an hour ahead of GMT
Special Lines of Parallels Latitude and Longitude
Some lines of latitude are special: one of them is the equator and the other two are the 30th parallels and the area between them and the equator is referred to as low latitude because they are generally warmer. Other two special lines of latitude are the 60th parallels. This is because the areas north and south of these 60th parallels are usually cold; hence they are referred to as high latitudes.
Regions; which fall between the 30th and the 60th latitudes in both the northern and southern latitudes; are referred to as middle latitudes and these regions experience four seasons- fall, winter, spring and summer.
This information can depict that the latitude of a place determines its climate because they determine the heat energy that a region is going to receive at a given time of the year.
The other special lines of latitude are the Tropic of Capricorn (23 degrees 30” S); Tropic of Cancer (23 degrees 30” N); the Antarctic Circle (66 degrees 30 S); and the Arctic Circle (66 degrees 30” N). These lines depict the earth’s tilting as it orbits the sun.
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