Compass

                             COMPASS

FINDING NORTH BY CONSTELLATIONS

 Star Method.

(1)   Less than 60 of approximately 5,000 stars visible to the eye are used by navigators. The stars seen as we look up at the sky at night are not evenly scattered across the whole sky. Instead they are in groups called constellations.

(2)   The constellations that we see depends partly on where we are located on the earth, the time of the year, and the time of the night. The night changes with the seasons because of the journey of the earth around the sun, and it also changes from hour to hour because the turning of the earth makes some constellations seem to travel in a circle. But there is one star that is in almost exactly the same place in the sky all night long every night. It is the North Star, also known as the Polar Star or Polaris.

(3)   The North Star is less than 1° off true north and does not move from its place because the axis of the earth is pointed toward it. The North Star is in the group of stars called the Little Dipper. It is the last star in the handle of the dipper. There are two stars in the Big Dipper, which are a big help when trying to find the North Star. They are called the Pointers, and an imaginary line drawn through them five times their distance points to the North Star. There are many stars brighter than the North Star, but none is more important because of its location. However, the North Star can only be seen in the northern hemisphere so it cannot serve as a guide south of the equator. The farther one goes north, the higher the North Star is in the sky, and above latitude 70°, it is too high in the sky to be useful.

(4)   Depending on the star selected for navigation, azimuth checks are necessary. A star near the north horizon serves for about half an hour. When moving south, azimuth checks should be made every 15 minutes. When traveling east or west, the difficulty of staying on azimuth is caused more by the likelihood of the star climbing too high in the sky or losing itself behind the western horizon than it is by the star changing direction angle. When this happens, it is necessary to change to another guide star. The Southern Cross is the main constellation used as a guide south of the equator, and the above general directions for using north and south stars are reversed. When navigating using the stars as guides, the user must know the different constellation shapes and their locations throughout the world.

Pace (unit)

A pace (or double-pace or passus) is a measure of distance used in Ancient Rome. It is the measure of a full stride from the position of the heel when it is raised from the ground to the point the same heel is set down again at the end of the step. Thus, a distance can be “paced off” by counting each time the same heel touches ground, or, in other words, every other step. In Rome, this unit was standardized as two gradūs or five Roman feet (about 1.48 metres or 58.1English inches). There are 1000 passus in one mille, and a mille was sometimes referred to as a mille passus.

The Byzantine pace or vema (βήμα [ˈvima]) was 2½ feet (pous)

A pace in modern terminology is usually taken as being a single pace rather than a double pace. It has no formal definition but is taken as being around 30 inches.

A directional compass is shown below.  It is used to find a direction or bearing.

The four main directions of a compass are known as cardinal points.  They are north (N), east (E), south (S) and west (W).  Sometimes, the half-cardinal points of north-east (NE), north-west (NW), south-east (SE) and south-west (SW) are shown on the compass.  The above compass shows degree measurements from 0° to 360° in 10° intervals with:

• north representing 0° or 360°
• east representing 90°
• south representing 180°
• west representing 270°

When using a directional compass, hold the compass so that the point marked north points directly away from you.  Note that the magnetic needle always points to the north.

Bearing

The true bearing to a point is the angle measured in degrees in a clockwise direction from the north line.  We will refer to the true bearing simply as thebearing.

For example, the bearing of point P is 065º which is the number of degrees in the angle measured in a clockwise direction from the north line to the line joining the centre of the compass at O with the point P (i.e. OP).

The bearing of point Q is 300º which is the number of degrees in the angle measured in a clockwise direction from the north line to the line joining the centre of the compass at O with the point Q (i.e. OQ).

Note:

The bearing of a point is the number of degrees in the angle measured in a clockwise direction from the north line to the line joining the centre of the compass with the point.
A bearing is used to represent the direction of one point relative to another point.

For example, the bearing of A from B is 065º.  The bearing of B from A is 245º.

Note:

• Three figures are used to give bearings.
• All bearings are measured in a horizontal plane. 

Boxing the compass is the action of naming all thirty-two principal points of thecompass in clockwise order.

Navigational compass mariner‘s compass (Larger)
#	Compass point	Abbreviation	True Heading
1.	North	N	0.00°
2.	North by east	NbE	11.25°
3.	North-northeast	NNE	22.50°
4.	Northeast by north	NEbN	33.75°
5.	Northeast	NE	45.00°
6.	Northeast by east	NEbE	56.25°
7.	East-northeast	ENE	67.50°
8.	East by north	EbN	78.75°
9.	East	E	90.00°
10.	East by south	EbS	101.25°
11.	East-southeast	ESE	112.50°
12.	Southeast by east	SEbE	123.75°
13.	Southeast	SE	135.00°
14.	Southeast by south	SEbS	146.25°
15.	South-southeast	SSE	157.50°
16.	South by east	SbE	168.75°
17.	South	S	180.00°
18.	South by west	SbW	191.25°
19.	South-southwest	SSW	202.50°
20.	Southwest by south	SWbS	213.75°
21.	Southwest	SW	225.00°
22.	Southwest by west	SWbW	236.25°
23.	West-southwest	WSW	247.50°
24.	West by south	WbS	258.75°
25.	West	W	270.00°
26.	West by north	WbN	281.25°
27.	West-northwest	WNW	292.50°
28.	Northwest by west	NWbW	303.75°
29.	Northwest	NW	315.00°
30.	Northwest by north	NWbN	326.25°
31.	North-northwest	NNW	337.50°
	North by west Before the Magnetic Compass was discovered, early map makers would draw a small 16 pointed circle on the map, and place an “N” to point to North. These were the 16 Cardinal Points from which the winds were thought to blow. This drawing was called a “Wind Rose.” When the magnetic compass came along, it was usually set on top of the Wind Rose pattern in order to help face the nautical chart in the proper direction. The wind rose started to become known as a COMPASS ROSE. Since the 1100’s, compass bearings have been split into 16 different directions: North – North North East – North East – East North East – East East – East South East – South East – South South East – South South South West – South West – West South West – West West North West – North West – North North West – North This was all the accuracy a Mariner’s Compass had to offer then. By today’s standards, it was not very accurate. As spherical mathematics improved, it became more customary to give bearings in units of “Degrees” from Geographic North. In the 1920’s, it became an accepted practice to indicate direction, called HEADING or BEARING, by a single number (0 to 360) representing degrees of a circle as measured clockwise from True North. The development of the compass instrument itself represents quite an achievement, however the actual use of this instrument is more of an art form. The Compass is not by any means a complex instrument. Anyone from 9 to 90 should be able to learn compass operation with just some practice and understanding a few simple principles.