Earth to experience a rare alignment
Compass navigators will have one less adjustment to make
The last time Greenwich, England, had zero declination, King Charles II was on the throne. But true north and magnetic north are about to align at the prime meridian for the first time in 300 years.
This is important for anyone who uses a compass to navigate. Usually, there is a degree difference between true north and magnetic north. For precise navigation, compass users need to adjust.
If you didn’t know already, there’s more than one “north” on Earth: Magnetic north is determined by our planet’s magnetic field lines, and true north refers to a geographic line along a meridian.
Depending on where you are on Earth, the angle between true north and magnetic north varies. In the U.S., for example,
the angle of declination can range from 20 degrees west or east.
We all know the Earth is constantly moving, but so is its magnetic field. “The line of zero declination, called the agonic, is moving westward at a present rate of around 20 K (about 12.5 miles) per year,” said the British Geological Survey.
This year, that westward movement is closing the gap between true and magnetic north just over Greenwich, England. This is noteworthy because Greenwich is home of the Royal Greenwich Observatory and, more important, the point of zero degrees longitude.
Also known as the prime meridian, it’s the birthplace of universal time. “The observatory paved the way for a global reference system for maps and navigation that we know today as the Greenwich Meridian, and with it, Greenwich Mean Time,” the British Geological Survey said.
Basically everyone, from 17th century astronomers to modern-day outdoor enthusiasts, uses the Greenwich meridian. It’s the reference point for all other longitudinal meridians, many charts and maps, and world time zones.
Compass reading just got easier, at least in England. For much of the rest of the world, magnetic north and true north still compete, and sometimes confuse, people employing compasses to navigate.
But the world — and compass needles — keep turning, so this convenient moment of synchronicity in Greenwich won’t last long.