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Introduction

 

 

 

The Earth.

 

The Earth is the third plant from the sun, in the solar system. It has one natural satellite, Called, Moon. The earth revolves around the sun, about every 365 days while completing rotation, on its axis about every 24 hours, from west to, east direction. The shape of the Earth is, considered a true sphere for most purpose.

 

The parallels of Latitude, and, Meridians of Longitude are, imaginary circles drawn on, Earth's surface to, find the co-ordinate of all the places on it. The co-ordinate of places in Latitudes, and, Longitudes provides, the positions of these places, on the Earth's surface. All the places on the Earth, obtain a single, and, non-repetitive global address by, way of Latitude, and, Longitude passing through that place.

 

 

Latitude

While lines of latitude run across a map east-west, the latitude indicates the north-south position of a point on earth.  

 

Lines of latitude start at 0 degrees at the equator and end at 90 degrees at the North and South Poles (for a total to 180 degrees of latitude). Therefore, the higher the value of degree of latitude, the closer it is to the North or South Pole.

 

 

Everything north of the equator is known as the Northern Hemisphere and everything south of the equator is known as the Southern Hemisphere.

 

 

Distance Between  Lines of Latitude

 

Lines of latitude are called parallels and in total there are 180 degrees of latitude.  The distance between each degree of latitude is about 69 miles (110 kilometers).  

 

What is a Parallel?

 

A parallel is a named line connecting all points along the same line of latitude.

 

Major Lines of Latitude (or Parallels)

 

The five major parallels of latitudes from north to south are called: Arctic Circle, Tropic of Cancer, Equator, Tropic of Capricorn, and the Antarctic Circle.

 

 

 

 

On a map where the orientation of the map is either due north or due south, latitude appears as horizontal lines.

 

 

Equator

 

The equator divides the earth into the Northern Hemisphere and the Southern Hemisphere is marks the location of 0 degrees latitude.   Latitude represents an angular distance north or south of the equator.

The equator marks the locations on earth that are equidistance from the North and South Poles.  The Equator is the only line of latitude that is a great circle, all the other lines of latitude are small circles.

 

 

 

 

Tropic of Cancer

 

The Tropic of Cancer marks the location where the sun reaches the zenith at this latitude.  

The summer solstice, which occurs on either June 20 or 21 of each year, marks the day on which the sun shines vertically over this parallel.

 

Tropic of Capricorn

 

Moving every year, the Tropic of Capricorn is the parallel line of latitude that is currently located at 23° 26′ 14.440″.

The winter solstice, which occurs on either December 21 or 22 of each year, marks the day on which the sun shines vertically over this line.

 

 

 

Arctic and Antarctic Circles

 

The Arctic and Antarctic Circles are the parallels of latitude that are roughly 66.5 degrees (66° 33′ 44″ (or 66.5622°).

The region above the Arctic Circle, which includes the North Pole, is known as the Arctic.

The region south of the Antarctic Circle, which includes the South Pole, is known as the Antarctic.

 

 

Our solar system consists of the Sun and a number of planets. The Earth which we live on is one of the planets. The Sun is one of the many stars in the sky but because it is much closer to us it appears much brighter and bigger. The Moon revolves around the Earth and is called a satellite.

The Earth is round like a ball but slightly flattened at the top and bottom like an orange. The upper end of the Earth is called the North Pole. The lower end is the South Pole.

 

 

 

The Equator is an imaginary line drawn around the middle of the earth. The Equator divides the earth into two parts. Each part is called a hemisphere. So, we have the Northern hemisphere and the Southern hemisphere. The portion of the earth from the equator to the North pole is the Northern hemisphere. The portion of the earth from the equator to the South pole is the Southern hemisphere.

 

 

 

 

Latitudes are imaginary lines drawn around the earth in an East-West direction and these lines are parallel to each other. The equator is one of the latitudes and is called Latitude 0°. As you move towards the North pole the Latitudes increase from 0° to 90° N. Similarly, as you move towards the South pole from the equator, Latitude increases from 0° to 90° S.

• Latitude lines run East-West and are parallel to each other.
• Latitude is measured from 0° to 90° N or S
• Latitude 0° is called the Equator
• Latitude 90° N is called the North Pole
• Latitude 90° S is called the South Pole
• Latitude is expressed in degrees and minutes North or South.
• Each degree of Latitude is equal to 60 minutes.
• Each minute of Latitude on the Equator is equal to one Nautical mile.

 

 

 

 

 

Meridians are lines joining the North and South poles. The meridian passing through Greenwich in UK is called the Prime Meridian. The Prime Meridian is Longitude 0°.

Longitude is measured from 0° to 180° E (East) and from 0° to 180° W (West). In the diagram you will notice that 180° E and 180° W is the same line.

Longitude is expressed in degrees East or West.

Longitude lines run North and South and are parallel to each other on a chart.

 

Position of a vessel is found by intersection of Latitude and Longitude on a chart.

 

 

 

Horse Latitudes

 

The Horse Latitudes are found at about 30 degrees North and South of the equator. Horse latitudes represents areas in the subtopics where prevailing winds diverge and flow towards the poles (known as westerlies) or towards the Equator (known as trade winds).

 

 

Longitude

 

Longitude lines run north-south and mark the position east-west of a point. Therefore, latitude is the angular distance east or west of the Prime Meridian.

Lines of longitude run from pole to pole, crossing the equator at right angles. All lines of longitude are equal in length. Each line of longitude also is one half of a great circle.

There are 360 degrees of longitude (+180° eastward and −180° westward.).The longitude line of 0 degrees is known as the Prime Meridian and it divides the world into the Eastern Hemisphere and the Western Hemisphere.

 

 

 

 

What is a Meridian?

 

While lines of latitude are known as parallels, lines of longitude are known as meridians.

 

 

How to Tell if a Meridian is East or West

 

Distances that are west of the Prime Meridian are noted with a negative in front of the number (negative numbers) and distances that are east of the Prime Meridian are positive numbers (-180 degrees degrees of longitude west and 180 degrees of longitude east).

 

 

Distance Between Lines of Longitude

 

The distance between longitudes narrows the further away from the equator. As you move toward the poles, the distance between each line of longitude becomes smaller until the converge at the North and South Poles.

The distance between longitudes at the equator is the same as latitude, roughly 69 miles. At 45 degrees north or south, the distance between is about 49 miles (79 km).

The distance between longitudes reaches zero at the poles as the lines of meridian converge at that point.

 

 

 

Prime Meridian

 

The line of longitude where the degree is zero is known as the Prime Meridian.  

 

 

 

Time Zones

 

 

 

As Earth rotates, different parts of Earth receive sunlight or darkness, giving us day and night. As your location on Earth rotates into sunlight, you see the sun rise. As different parts of Earth enter daylight at different times, we need different time zones.

 

The Earth takes 24 hours to rotate once. So, we have 24 Time Zones. Ships in Time zone 0 keep Universal Time Coordinated or UTC. Till 1972 this was known as Greenwich Mean Time or GMT, because this is the time kept at the Prime Meridian which passes through Greenwich in the UK.

 

If a ship sails eastwards from Longitude 0° to Longitude 15° East, she will be in time zone +1. If the time is 1200 hours at longitude 0°, the time at longitude 15° E will be 1300 hours.This means that the time at longitude 15° E will be UTC +1.

 

If a ship sails westwards from Longitude 0° to Longitude 15° West, she will be in time zone “-1”. If the time is 1200 hours at longitude 0°, the time at longitude 15° W will be 1100 hours. This means that the time at longitude 15° W will be UTC -1.

 

As ships sail eastwards, they have to advance the ship’s clock by 1 hour for every 15° change in longitude and retard the clock when sailing westwards.

 

 

Standard Time

 

This is the official time for an entire country or part of a country based on one of the longitudes passing through that country. Indian Standard Time  or IST is UTC +5.5

 

International Date Line

 

Longitude 180° (E or W) is the longitude through which the International Date Line passes.

 

If a vessel crosses the date line while sailing East, she has to retard her date by one day.

 

If a vessel crosses the date line while sailing West, she has to advance her date by one day.

 

For the convenience of some countries, the International Date Line goes around some islands near Longitude 180°. It also deviates to pass between the Soviet Union and North America.

 

 

International Date Line

 

The line on Earth where one calendar day becomes the next is known as the International Date Line (IDL).  The line is generally found 180 degrees from the Prime Meridian but the line circumvents some regions and islands to avoid dividing contiguous pieces of regions and countries into two separate days.  

 

There are 23 one-hour slices and two 30 minutes slices that divide the world up into different time zones.  Traveling from east to west over the International Date Line advances the calendar by one day.

 

The black line on this map shows the International Date Line.