The Handy Geography Answer Book. Paul A Tucci

navigators?

      In 1730, the sextant was invented independently by two men, John Hadley and Thomas Godfrey. Using a telescope, two mirrors, the horizon, and the sun (or another celestial body), the sextant measures the angle between the horizon and the celestial body. With this measurement, navigators could determine their latitude while at sea.

      When was the compass invented?

      Ancient south-pointing compasses have been found in China, dating back to as early as 200 B.C.E., during the Han Dynasty period. These early, metal compasses pointed south and helped Chinese mariners stay on course at sea. It was not until 1600 C.E. that the use and innovation of the compass had migrated to Europe. As early as the eleventh century, the Chinese were using a magnetic needle to determine direction and to foretell events. At approximately the same time, the Vikings may have also used a similar device. A compass is simply a metallic needle that points toward the Magnetic North Pole.

      Have compasses always pointed north?

      No, they have not. Though compasses always point to the magnetic pole, the magnetic pole has not always been in the north, as it always moves. Every 300,000 to 1 million years, the magnetic pole flips from north to south or from south to north. If compasses had been around before the last time the magnetic pole reversed, their arrows would have pointed south rather than north.

      What is true north?

      True north is the direction that one can map along the surface of the Earth to the geographic North Pole.

      What is Magnetic North?

      Magnetic North refers to the direction that corresponds to the magnetic field lines to which compasses point. The core of the Earth acts like a giant spherical magnet, with two poles: one North and one South. The strength of the magnetic field changes with time and location. The main field that lies far below the surface of the Earth generates approximately 90% of the total magnetic field. The other 10% of Earth’s magnetic field is generated in our upper atmosphere and magnetosphere, where ions, electrons, and other particles help protect the planet from dangerous solar emissions.

      What is a compass rose?

      On old maps, the directions of the compass were represented by an elaborate symbol, known as a compass rose. Many of the older compass roses displayed 32 points, representing not only the four cardinal directions (north, south, east, and west) but also 28 subdivisions of the circle (southwest, south-southwest, etc.). This directional symbol resembled a rose, hence its name. Though compasses are now often drawn with only the four cardinal directions and the resemblance to the flower is minimal, the directional symbol is still called a compass rose.

      What is an azimuth?

      Azimuth is another method for stating compass direction. It is based on the compass as 360 degrees, with north at 0 degrees, east at 90, south at 180, and west at 270 degrees. You can refer to a direction as “head 90 degrees” instead of “head east.”

      How and why does Magnetic North move?

      Scientists aren’t sure why the Earth’s magnetic pole moves, only that it does. The European Space Agency’s SWARM mission launched three satellites in November 2013 to analyze the Earth’s magnetic fields, contributing significant data for global researchers.

      How much has the Magnetic North Pole moved?

      Since it was documented in 1831 by James Ross to be slightly north of 70 degrees north latitude, it has moved to north of 80 degrees north latitude at an average rate of more than 24 miles (40 km) per year. The amount of movement from decade to decade varies, but it’s never more than a few miles each year. During the twentieth century, the pole moved approximately 6.2 miles (10 km) per year. At the beginning of our current century, researchers have measured the movement to be as many as 24.85 (40 km) miles per year.

      Unlike the geographic North Pole, the Magnetic North Pole does not stay in the same place but has shifted hundreds of miles over the last centuries.

LATITUDE AND LONGITUDE

      Where is the equator?

      The equator is the line located equidistant between the North and South Poles. The equator evenly divides the Earth into the Northern and Southern Hemispheres and is zero degrees latitude.

      What are lines of latitude and longitude?

      Lines of latitude and longitude make up a grid system that was developed to help determine the location of points on the Earth. These lines run both north and south and east and west across the planet. Lines of latitude (those that run east and west) begin at the equator, which is zero degrees. They extend to the North Pole and the South Pole, which are 90 degrees north and 90 degrees south, respectively. Lines of longitude (those that run north and south) begin at the Prime Meridian, which is the imaginary line that runs through the Royal Observatory in Greenwich, England. The lines of longitude extend both east and west from the Prime Meridian, which is zero degrees, and converge on the opposite side of the Earth at 180 degrees.

      Are lines of longitude and latitude all the same length?

      No, they are not. Only the lines of longitude are of equal length. Each line of longitude equals half of the circumference of the Earth because each extends from the North Pole to the South Pole. The lines of latitude are not all equal in length. Since they are each complete circles that remain equidistant from each other, the lines of latitude vary in size from the longest at the equator to the smallest, which are just single points, at the North and South Poles.

      How wide is a degree of longitude?

      Though there are only a couple dozen lines of longitude shown on most globes and world maps, the Earth is actually divided into 360 lines of longitude. The distance between each line of longitude is called a degree. Because the lines of longitude are widest at the equator and converge at the poles, the width of a degree varies from 69 miles (111 km) wide to zero, respectively.

       Do other planets have longitude and latitude lines?

      Yes, scientists have divided the other planets and their moons into longitude and latitude systems like the Earth. They use these lines just as they do on Earth: to pinpoint exact locations on the planet or moon.

      Lines of latitude go from side to side (east and west) on this map, while lines of longitude run top to bottom (north and south).

      How wide is a degree of latitude?

      Though there are only about a dozen lines of latitude shown on most globes and world maps, the Earth is actually divided into 180 lines of latitude. The distance between each line of latitude is called a degree. Each degree is an equal distance apart, at 69 miles (111 km).

      What do minutes and seconds have to do with longitude and latitude?

      Each degree of longitude and latitude is divided into 60 minutes. Each minute is divided into 60 seconds. An absolute location is written using degrees (°), minutes (′), and seconds (″) of both longitude and latitude. Thus, the Statue of Liberty is located at 40°41′22″ North, 74°2′40″ West.

      Which comes first, latitude or longitude?

      Latitude is written before longitude. Latitude is written with a number, followed by either “north” or “south” depending on whether it is located north or south of the equator. Longitude is written with a number, followed by either “east” or “west” depending on whether it is located east or west of the Prime Meridian.

       Why was the Prime Meridian established at Greenwich?

      In 1675 the Royal Observatory in Greenwich, England, was established to study determination of longitude. In 1884, an international conference established the Prime Meridian as the longitudinal line that