Dan Joling of Anchorage captured this image of the full moon over Alaska’s largest city on Jan. 6, 2023. (Courtesy Photo / Dan Joling)

Alaska Science Forum: Magnetic declination and finding the moon

Dan Joling of Anchorage was set to photograph the full moon rising over the Port of Anchorage on Jan. 6, 2023. His research told him the moon would pop over the horizon at a certain number of degrees from north. Guided by the compass feature on his iPhone, Joling aimed his camera that way.

He waited. Suddenly, the moon rose far to the left of where he expected. He jumped in his car and drove to an overlook near West High School. There, he captured the shot with the backdrop he wanted.

What went wrong? Joling’s phone did not calculate the difference between magnetic north and true north.

True north is the straight-line direction toward the geographic north pole of the Earth. Magnetic north, the default setting of Joling’s phone compass, is often many degrees off from true north, depending on where you are on the planet.

Dan Joling of Anchorage captured this image of the full moon over Alaska’s largest city on Jan. 6, 2023. (Courtesy Photo / Dan Joling)

True north is the north displayed on maps. Most GPS units adjust automatically for the difference between magnetic north and true north.

What is magnetic north, and why does an old-school compass needle point to it? Because Earth is a giant magnet.

Deep within our planet is a liquid core, a ball of molten iron and nickel. It is slightly smaller than the moon. When the core rotates, the sloshing of molten iron and nickel produces an electric current, which produces a magnetic force. Ground zero for this force is the elusive spot known as the magnetic north pole.

The magnetic north pole is now north of Canada’s arctic islands, hundreds of

miles south of the geographic north pole. It drifts more than 25 miles each year, and seems to be headed for Siberia.

The difference between magnetic north and true north is known as degrees of declination.

The Fairbanks declination I set on my works-with-no-battery handheld compass in 2003 adjusted for a geographic north reading that was 24 degrees west of magnetic north. If I were to find that compass in my closet today, I would need to change the declination by twisting a disc within its face. True north in Fairbanks is now just 16 degrees west of magnetic north.

Some places, like anywhere near the Mississippi River (which coincidentally runs the same direction as a magnetic-field line), are currently at about zero degrees declination. True north in Anchorage is now 15 degrees west of magnetic north, in Juneau is 18 degrees west, and in Nome is 3 degrees west.

To adjust for that declination, smartphone users need only to open the settings for their digital compass. There will be a switch (the iPhone’s says “Use True North”) that automatically calibrates to wherever you are on the planet.

• Since the late 1970s, the University of Alaska Fairbanks’ Geophysical Institute has provided this column free in cooperation with the UAF research community. Ned Rozell, ned.rozell@alaska.edu, is a science writer for the Geophysical Institute.

More in News

Folks at the Alaska State Capitol openly admit to plenty of fish tales, but to a large degree in ways intended to benefit residents and sometimes even the fish. (Mark Sabbatini / Juneau Empire)
The bizarre bills other state legislatures are considering

Alaska’s Legislature isn’t mulling the headline-grabbers some statehouses have in the works.

This photo shows snow-covered hills in the Porcupine River Tundra in the Yukon Territories, Canada. In July 1997, a hunter contacted troopers in Fairbanks, Alaska, and reported finding a human skull along the Porcupine River, around 8 miles (13 kilometers) from the Canadian border. Investigators used genetic genealogy to help identify the remains as those of Gary Frank Sotherden, according to a statement Thursday, Feb. 2, 2023, from Alaska State Troopers. (AP Photo / Rick Bowmer)
Skull found in ‘97 in Interior belongs to New York man

A skull found in a remote part of Alaska’s Interior in 1997… Continue reading

(Michael Penn / Juneau Empire File)
Police calls for Saturday, Feb. 4, 2023

This report contains information from law enforcement and public safety agencies.

Officer William Hicks stands with JPD Chief Ed Mercer and Deputy Chief David Campbell during a swearing in ceremony for Hicks on Thursday at the JPD station in Lemon Creek. (Jonson Kuhn / Juneau Empire)
New officer joins JPD’s ranks

The Juneau Police Department welcomed a new officer to its ranks Thursday… Continue reading

These photos show Nova, a 3-year-old golden retriever, and the illegally placed body hold trap, commonly referred to as a Conibear trap, that caught her while walking near Outer Point Trail last week. (Courtesy / Jessica Davis)
Dog narrowly survives rare illegally placed trap in Juneau

State wildlife officials outlined what to do if found in similar situation

Gavel (Courtesy photo)
Public defender agency to refuse some cases, citing staffing

ANCHORAGE — A state agency that represents Alaskans who cannot afford their… Continue reading

(Michael Penn / Juneau Empire File)
Police: Gift card scam connected to hoax Fred Meyer threats

This article has been moved in front of the Empire’s paywall. A… Continue reading

This is a concept design drawing that was included in the request for proposal sent out by the Alaska Department of Transportation and Public Facilities seeking outside engineering and design services to determine whether it’s feasible to build a new ferry terminal facility in Juneau at Cascade Point. (Alaska Department of Transportation and Public Facilities)
DOT takes steps toward potential Cascade Point ferry terminal facility

It would accommodate the Tazlina and or Hubbard, shorten trips to Haines and Skagway

(Michael Penn / Juneau Empire File)
Police calls for Friday, Feb. 3, 2023

This report contains information from law enforcement and public safety agencies.

Most Read