COURSES

TRUE COURSE

True course is the angel at the ships between true North and the ships head,that is the angel between the true meridian and the ship's fore and aft line.


TRUE BEARING

True bearing of an object is the angle at the observer between true North indicated by the meridian and the line joining the observer and the object.

DEVATION

MAGNETIC COURSE

Magnetic course is the angel at the ships between magnetic North and the ships head,that is the angel between the magnetic meridian and the ship's fore and aft line.

MAGNETIC BEARING

 The Magnetic bearing of an object is the angle at the observer between magnetic North indicated by the magnetic meridian and the line joining the observer and the object.

DEVITAION  

The angel which the compass needle makes with the magnetic meridian is known as the deviation.

It is termed East,If the compass North lies to the East or left of the magnetic North

The deviation of a compass varies as the ships head changes.For the same ships head,deviation remains the same for all bearing as deviation,depends on the ships head and not on a bearing

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EARTH

MAGNETIC MERIDIAN

Magnetic meridians are lines joining the magnetic poles of the earth.

PRIME MERIDIAN

Prime meridian is the meridian which passes through green-which,other meridian are named East or West from the prime meridian

VARIATION

The magnetic poles are not in the same potions as the geographic poles,there is an angel between the magnetic and the geographic meridian.The angel between them known as the VARIATION.

Variation is different at different places.It id termed East,if the magnetic North lies to East or right of the true North.,and West if the magnetic North lies West or left of the true North.

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D'lat and D'long

DIFFERENCE IN LATITUDE (D'lat )


The D'lat  between two places is the arc of the meridian or angel at the center of  the earth contained between parallels latitude through the two places.
D'lat is named North or south according to the direction from the first place to the second.


DIFFERENCE IN LONGITUDE (D'lat )

The D'long  between two places is the shortest arc of the equator or the smaller angle at the poles contained between the meridian through the two places.
D'long is named East or West according to direction from the first place to second place.

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CELESTIAL NAVIGATION

                                                            ECLIPTIC

Ecliptic is a great circle on the celestial sphere in the same plane as the plane of the earth's orbit around sun.Thus the sun's apparent annual path on the celestial sphere is Ecliptic 





OBLIQUITY OF THE ECLIPTIC




Is the angel between the plane of the equinoctial and that of ecliptic
It is value approximately 23.5 degrees

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Direction of the Earth

Direction of the Earth


For the purpose of the navigation,direction on the earth surface is measured as an angel from the meridian where the observer is located.There are two commonly used systems for indicating direction


01. QUADRANTAL NOTATION


02.THREE FIGURE NOTATION


QUADRANTAL NOTATION


The angel measured from North to East or West and South to East or West

THREE FIGURE NOTATION 

The angel measured clockwise from the North 000  to 360 degrees

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GHA AND LHA

GREENWICH HOUR ANGEL (GHA)


GHA of a body is the arc of the equinoctial,or the angel at the celestial pole,measured  westerly from the celestial meridian of Greenwich to the celestial meridian passes through that body




LOCAL HOUR ANGEL (LHA)


LHA of a body is the arc of the equinoctial,or the angel at the celestial pole,measured  westerly from the observer's celestial meridian to the celestial meridian.

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EARTH

                                                                 Shape of the Earth


The earth is not true sphere.It's shape os that of an oblate spheroid,the equatorial diameter being more than the polar diameter.

AXIS

The axis of the earth is diameter which about it rotates

POLES

The geograph poles of the earth are two points  where the axis meets the earth surface.
The earth rotates about it's axis once each day.This rotation carries each point on the earth surface towards East West  in the direction 180 degrees from East,North is the direction 90 degrees to the left of the East & South the direction  90 degrees to the right of the East.The two poles of the earth designed North pole & South pole accordingly. 

GREAT CIRCLE 

Great circle is a circle on the surface of the sphere,the plane which passes through the center of the sphere.
There is only one great circle through any two points on the sphere's surface,except if the points are two ends of the diameter when infinite number of great circles are possible.

A great circle is the longest line that can be drown around the earth,A segment of the earth great circle is the shortest distance between two points on the earth surface.

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