## Basic geographical notions

A diameter around which the Earth is turning is an axis of the Earth, ends of that axis are poles: north and south. The zero parallel i.e. the equator are coming into existence by cutting in two the Earth with the perpendicular to the axis of the Earth and going through its middle. The equator is dividing also the globe into two hemispheres: north and south.

Parallels are circles about smaller than the ray of the Earth radii and parallel to the equator, their plain aren't going through the middle of Land. Meridians are circles about the rays equal of the ray of the Earth and running across poles north and noon, their plains are going through the middle of Land. The prime meridian is running across the London Greenwich district and he is dividing the globe into two hemispheres: east and west.

### Geographical longitudes and latitudes

Longitude λ (upper and bottom scale on the map)
It is angle measure between the prime meridian (Greenwich) and with free different meridian. The longitude is being measured up from the prime meridian to the east or the west. A letter is a symbol of the longitude λ.
All points to the east of the Greenwich meridian (from 0 to 180°) they have the eastern length, so at the recording of coordinates a sign is being added [+] or oh and is writing this way:
λ = +012° 47,3'
or so:
λ = 012° 47,3' E
All points west of the Greenwich meridian (from 0 to 180°) they have the west length, at the recording of coordinates a sign is being added [-] or in and is enrolling this way:
λ = -012° 47,3'
or so:
λ = 012° 47,3' W

The 180° meridian is international date line.

Latitude φ (right and left scale on the map)
It is angle measure between the equator and the free different parallel. The latitude is being measured up from the equator for the midnight or the noon. He is a symbol of the latitude φ.
All points to the north of the equator (from 0 to 90°) of May north breadth, so at the recording of coordinates a sign is being added [+] or N and is writing this way:
φ = +55° 32,5'
or so:
φ = 55° 32,5' N
All points to the south of the equator (from 0 to 90°) they have the southern breadth, at the recording of coordinates a sign is being added [-] or S and is enrolling this way:
φ = -55° 32,5'
or so:
φ = 55° 32,5' S

This way so putting the yacht at sea is determining two coordinates: the length and the latitude. In practice he often enrols coordinates of the position into this way:

φ 55° 32,5' N ; λ 012° 47,3' E

The longitude and the latitude are being measured up in steps, minutes and seconds, where:

1° = 60'
1' = 60''

### The horizon

Horizon of the observer - it is the plain distant from the surface of the Earth at the so-called optic height (that is distance equal of raising eyes of the observer above the surface of the Earth) and perpendicular to the clearing of the sector running across the place of the observer and the centre of Land.

True horizon - it is a parallel to the horizon of the observer and going through the middle of Land plain. The sight of the observer is limited by the ruler of the horizon and he is depending on the optic height.

Knowing the height of raising eyes of the observer (h) it is possible easily to calculate the distance to the horizon what in certain situations can be essential (e.g. assessment of distance dividing the yacht from the edge). We are calculating the distance from the model.

Calculate the distance to the horizon

 Height of raising eyes of the observer: describe the individual: feet meters Distance to the horizon (nautical miles):

We can use the line and to calculate the distance to the object about the known height (e.g. lights of the lighthouse) using the moment in which the light is hiding behind the horizon. Best to capture such a moment when the light is visible for the observer standing aboard and invisible for the sitting observer.

Compute the Geographic Range

 Height of the lighthouse above sea level: describe the individual: feet meters Height of raising eyes of the observer above sea level: describe the individual: feet meters Distance (nautical miles):

Deducing the formula
 Using the Pythagoras theorem for a right-angled triangle OBC it is possible to deduce the formula to the distance to the horizon. AB = h (height of eyes of the observer above sea level in meters) OA = OC = r (ray of the Earth) BC = d (searched distance to the horizon of the observer) BO = h + r CO = r so BO2 = BC2 + CO2 (h + r)2 = d2 + r2 and far because We are placing the mean of the ray in front of the globe R = 6370 x 103 m and we are sharing the result through 1852 m in order to get nautical miles. The composite density is causing atmospheres that rays of light are surrendering to the certain breakdown, so the distance to the horizon will be a little bit bigger. After all for the average the pattern is longing for the refraction this way: For the same reasons a rough formula is often practiced, where instead of value 2,08 we are putting value 2. Cursory determining the optic height, the changing visibility and changes in the refraction are causing that one should treat the result with the big carefulness.

### Loxodrome and Great Circle Sailing

The running along the surface area of the globe, cutting geographical meridians across line under the identical angle is being named loxodrome. If this angle will be equal of the nought it loxodrome will agree with one of geographical meridians. If the angle will be equal of 90° - will agree with one of geographical parallels. It is possible so to say, that loxodromes there are all meridians and geographical parallels. In remained cases he is creating the spiral line which gradually is making its way towards the pole.

Straight line crossed off on the map of Mercator (course) he always cuts meridians across under the same angle so he is loxodrome. The yacht holding such a trip with the account of the compass is moving after loxodrome - that is not along the shortest way (behind the shutdown when loxodrome one of geographical meridians or the equator are).

On the globe between two points he is the shortest distance great circle sailing, that is segment of the great circle which is contained between these points. great circle sailing and loxodroms there are only an equator and geographical meridians. Choosing the navigation after ortodromie the biggest benefits are being received at covering big distances, above 500Mm, in the distance from the equator when a point of departure and the destination are lying on the latitude moved close.

Crossed off on the map of Mercator great circle sailing is a curve bulged towards the closer pole. Navigating traditional methods navigation after ortodromie is becoming quite complicated what isn't making the more considerable problem if the yacht is equipped with appropriate devices (e.g. C-MAP). Navigation after great circle sailing is nothing else like navigation loxodrome, since is taking place with segments loksodromy. And a right computer program in combination with the GPS receiver can systematically correct the run of the yacht. More about traditional methods of calculating great circle sailing you will find here .

You can also use around Great Circle Sailing leading coordinates of the home position and the destination position will design the computer optimal great circle sailing.

The text is in the preliminary translation. I am apologizing for mistakes in the text and I am asking for understanding.