Magnetic North Pole Remains Elusive
True north and magnetic north are the same in some parts of the world, but not in Alaska. Compass users in the north need to readjust them every few years for declination, the difference between true and magnetic north, because of the extreme effects of Earth's magnetism at high latitudes.
Bill Worthington, a geophysicist who works for the U.S. Geological Survey in Fairbanks, knows more about magnetic declination than most people. He oversees the College
Magnetic Observatory, home to a few instruments that are about 1,000 times more sensitive to Earth's magnetic field than a hand-held compass.
Worthington recently invited me out to the observatory, which sits in a circular clearing of 46 acres on the wooded campus of the University of Alaska Fairbanks. The USGS formerly housed its sensitive instruments in buildings closer to the core of campus, but the steel in the chassis and engines of large vehicles passing by caused disturbances in magnetic field readings, inspiring the move to its more remote location.
Worthington gave me a tour of two wooden buildings held together with copper nails so as not to affect the magnetometers, instruments that measure Earth's magnetic field. Earth acts like a giant magnet because of its core, which resembles a ball of molten iron and nickel slightly smaller than the moon. When the core rotates, the motion of molten iron and nickel produces an electric current, and with it a magnetic force.
If a person stood on the magnetic north pole and tilted his or her compass vertical, its needle would point straight down. He or she would also need to be dressed in warm but breathable clothing, because the magnetic north pole is as far north as its name suggests, and it is always on the move.
The magnetic pole migrates about 10 kilometers northwest each year, and it has strayed around the north for thousands of years, at one point dropping to the latitude of Anchorage. When Canadian scientists flew onto the sea ice to locate the magnetic north pole in 2001, they found it at latitude 81.3° north and longitude 110.8° west, about 155 miles north of Ellef Ringnes Island.
Magnetic north is hard to pin down, sometimes moving up to 50 miles each day due to the effects of the solar wind, particles from the sun that also produce the aurora. True or geographic north, the northern point of Earth's axis, is always faithful to its name. The north on U.S. topographic maps is true north.
To make compasses useful, people need to adjust them for declination, the difference between magnetic and true north. Global positioning system receivers calculate declination automatically from models based on satellite data and information from magnetic observatories, such as the College Magnetic Observatory. For those who prefer the old-fashioned compass, USGS maps list the declination at the time they were made and conversions for years following, but the math can get clunky.
"If you have a map produced in the 1960s, there's been 40 years (of magnetic north's) movement since then," Worthington said. "That's a lot of extrapolation."
An easier way to find your declination is to go to the USGS website at http://geomag.usgs.gov/ and plug in your latitude, longitude, and the date. I've saved you the trouble for some Alaska locations: The declination in Fairbanks is about 24 degrees east, Anchorage is 21, Tok is 25, Ketchikan is 23, Kodiak is 19, Nome is 14, and Attu is 8.
These numbers are good for 2003, but the wandering of the magnetic north pole assures they won't be in a decade.
