Polar Husky A to Z
Compass
The gyrocompass, which is unaffected by the magnetism of the earth, consists of a gyroscope, with the spinning wheel on an axis confined to the horizontal plane so that its axle aligns itself with the north-south line parallel to the axis of the rotation of the earth, thereby indicating true north.
The Magnetic North Pole
Contrary to the popular belief, the bobbing needle on a compass does not point to the North Pole at the top of our planet. Instead, the magnetized needle of every compass points to a spot on the map just off the northern coast of Bathurst Island at 76.5 degrees north latitude in the Canadian High Arctic. This invisible spot, known as the magnetic North Pole, is actually 965 miles (1550 km) south of the geographic North Pole.
To make the situation even more interesting, the position of the magnetic pole wanders just a little each year, a phenomenon known as polar wandering. The direction of wandering has been observed to reverse. During geologic history the polarity of the earth's magnetic field has periodically reversed. When it was first discovered in 1831 the magnetic north pole was 465 miles farther south than it is today.
For these reasons, using a compass in the arctic requires very good navigational skills. Today, people are fortunate in that a technology known as GPS (Global Positioning System) is an affordable and an easy to use tool. By locating 3 or more satellites in orbit, it can pinpoint your location to within 200 yards. One drawback to GPS units is that they run on batteries, which in the extreme cold weather do not function very well. So it is wise that you know how to navigate with a compass as a back up.
Graticule
Latitude (lat.) is the angle between any point and the equator. Lines of constant latitude are called parallels. They trace circles on the surface of Earth, with each pole being 90 degrees (North Pole 90° N; South Pole 90° S).
The equator, an imaginary line that divides the globe into the Northern and Southern Hemispheres, is located at 0° latitude.
Longitude (long.) is the angle east or west of an arbitrary point on earth: The Royal Observatory, in Greenwich, England is the international zero-longitude point (long.=0 degrees). The antipodal meridian of Greenwich is both 180° W and 180° E. Lines of constant longitude are called meridians. The meridian passing through Greenwich is the Prime Meridian. Unlike parallels, all meridians are halves of great circles, and meridians are not parallel: they intersect at the north and south poles.
By combining these two angles, the horizontal position of any location on Earth can be specified.
For example, Baltimore, Maryland (in the United States) has a latitude of 39.3° North, and a longitude of 76.6° West (39.3° N 76.6° W). Therefore, a vector drawn from the center of earth to a point 39.3° north of the equator and 76.6° west of Greenwich will pass through Baltimore.
This latitude/longitude "webbing" is known as the common graticule.
Traditionally, degrees have been divided into minutes ( _ ) and seconds ( _ ). There are several formats for degrees, all of them appearing in a lat.-long. order:
DM Degree:Minute (49:30.0-123:30.0) DMS Degree:Minute:Second (49:30:00-123:30:00) DD Decimal Degree (49.5000-123.5000), generally with 4 decimal numbers.
To change from DM or DMS to DD, Decimal degrees = whole number of degrees, plus minutes divided by 60, plus seconds divided by 3,600.
Time Out for Fun
- Make your own compass! Learn more >>
- Fun Compass Games. Learn more >>
Links to Learn More
- Discover the secrets of ancient navigation. Learn more >>
- Find the exact locations of your favorite cities around the world! Learn more >>
Source courtesy of: en.wikipedia.org
