MAGNETIC COMPASS
Before the development of sophisticated electronic and sound detection systems, navigators calculated directions from objects in the sky the sun, the North Star, and the moon. A much more reliable guide for finding direction is a magnetic compass, which works at all times and in most places. When a piece of magnetized iron is placed on a splinter of wood and floated in a bowl of water, the wood will swing until the iron is pointing north and south. Any other direction then can be found.
In China and Europe the magnetized iron found in the lodestone, a naturally occurring magnetic ore, was used to make a floating compass in the 12th century. Soon afterward it was discovered that an iron or steel needle touched long enough by a lodestone also had the tendency to align itself in a north-south direction. A small pocket compass works on the same principle as the first crude compass: instead of a lodestone and a wood splinter, it has a magnetized needle that swings on a pivot to indicate north. Larger compasses have two or more parallel needles attached to the underside of a disk called a compass card.
The compass works because the Earth itself is a huge magnet. Its magnetic poles are oval areas about 1,300 miles (2,100 kilometers) from the geographic North and South poles. Irregular lines of force connect the magnetic poles, and the compass needle simply aligns itself with these lines of force.
In a few places, where lines of force happen to lie along meridians (that is, where magnetic north and true north coincide), the compass points to true north. Near the magnetic pole the magnetic compass is useless because there the lines of force are vertical straight down into the Earth. In other areas iron ore deposits affect the compass's accuracy. Generally, however, the magnetic compass points a little east or west of true north.
The angle between true north and magnetic north is called variation or declination. Magnetic north is along the oval shape, whereas the true north is the geographical top of earth.
A compass dial or card usually has direction pointers consisting of 32 points.
1. The four principle, or cardinal, points are north, east, south, and west. They are marked N, E, S, and W.
2. Between these lie the intercardinal points, such as northeast (NE), northwest (NW), southeast (SE) and southwest (SW).
3. Further division gives such points as north-northeast (NNE). A final division is by points, such as north by east (N by E).
4. Naming all the points of a compass in their order is called boxing the compass.
Surveyors, navigators, and similar technicians need more exact directions they use degrees.
The compass Dial or Card has 360 degrees marked on it.
North is 000° (or 360°);
East, 090°;
South, 180°; and
West, 270".
In an effort to develop a navigational instrument whose accuracy would be unaffected by stray magnetic fields, the gyrocompass, which does not use magnetism, was developed. Gyrocompasses are often used in modern navigation systems because they can be set to point to true north rather than to magnetic north. Today large ships carry both magnetic compasses and gyrocompasses. Special compasses have also been developed for airplanes and other most advances space age equipments.
Magnetic Anomalies
Magnetic anomalies may be caused by the following reasons:
1. Reading while sitting in a car or other vehicle having steel components
2. Near a radio equipment
3. Near magnetic ores
4. Near or under high electric wires
5. Readings in great depths
6. Disturbances on the surface of Sun i.e. solar flares or such other reason which are rare and certain duration.
Sun Rise is always shifting and so is not very reliable to find direction instantly.
Parameters of Earth and relationship with Sun:
Earth Diameter at Equator : 12,756 km.
Earth Diameter at Polar Region : 12,714 km.
Earth's Rotation period round its axis
(From West to East) : 23 hrs 56 Mts & 4.091 Secs
Earth's distance from Sun : 149,597,900 kms.
Earth's speed of orbit round the Sun : 107,220 kms per hour.
Earth's rotation time round the Sun : 365 days 5 hrs 48 mts & 45.51 sec
On June 22 every year the Sun shines vertically on the Tropics of Cancer and this date is termed as summer solstice for Northern Hemisphere and winter solstice for the Southern Hemisphere. Likewise, on December 22, the Sun shines vertically on the Tropics of Capricorn.
On March 21 (called vernal equinox) and September 23 (called autumnal equinox) every year the Sun shines directly on the Equator when day and night are almost equal throughout the world.
Tropics of Cancer which is 23.5 degrees north of equator and tropics and Capricorn which is 23.5 degrees south of equator, thus encloses the hottest zone of the earth called the torrid zone.
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