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Today in science: Finding magnetic south

On January 16, 1909, a team of Antarctic explorers thought they’d found the magnetic south pole. Then, a few years later, they began to have doubts.

Explorers of the southern continent of Antarctica – Douglas Mawson, Alistair MacKay and Edgeworth David – on January 16, 1909 at the South Magnetic Pole. Image via Wikimedia Commons.

January 16, 1909. On this date, three members of an Ernest Shackleton expedition to Antarctica – Edgeworth David, Douglas Mawson and Alistair Mackay – raised a British flag and recorded the moment by photograph at what they thought was Earth’s South Magnetic Pole.

Four months earlier, they’d left McMurdo Sound, at the sea edge of the Antarctic continent, on a journey inland to find magnetic south, the point where the direction of Earth’s magnetic field comes out of the ground and points vertically upwards.

This was several years before a team led by Norwegian explorer Roald Amundsen reached the geographic South Pole on December 14, 1911.

Magnetic north and south are offset from geographic north and south. Illustration via cyberphysics.co.uk.

Like all Antarctic journeys of that time, the search for magnetic south was grueling. In this case, the men had to haul their own sledges by hand through a completely unknown region. Crevasses – deep gashes in the ice – slowed them down. When it became clear the march was taking longer than expected, the men had to reduce their rations.

But by early January, 1909, the team appeared to be on the polar plateau, where the thin air made breathing more difficult and where, on January 11, David recorded the temperature at minus 12 degrees Fahrenheit (-24 degrees Celsius). Finally, on January 15, Mawson calculated that they were about 13 miles (21 km) from magnetic south. The men left their heavy gear and made a final push to a point on Earth’s globe at 72°25′ South latitude, 155°16′ East longitude.

They raised the Union Jack and took their photo. They then immediately began making their way back to the ship Nimrod, which had carried Shackleton’s team from New Zealand to the southern continent of Antarctica the previous year.

Locations of Magnetic South Pole, or dip pole, over time. Comparison of direct observations with model predictions.  Image via NOAA

Locations of South Magnetic Pole, or dip pole, over time. Comparison of direct observations with model predictions. Image via NOAA

Mawson would later realize that he’d overlooked some important calculations made several years previously by another researcher. In 1913, Edgeworth David admitted that their party had reached only “an outlier of the main magnetic pole,” not the true South Magnetic Pole itself.

Yet their valiant effort is still remembered both in the history of science and in polar exploration.

Even if they had found the true point of magnetic south in 1909, that point would no longer be the South Magnetic Pole today. The North and South Magnetic Poles are wandering points on Earth’s surface. They move, due to changes in Earth’s magnetic field.

The location of the South Magnetic Pole is currently off the coast of Antarctica and even outside the Antarctic Circle.

Observed location of magnetic south during 1903 – 2000 are yellow squares. Modeled pole locations from 1590 to 2020 are circles progressing from blue to yellow. Illustration via NOAA.

Bottom line: On January 16, 1909, a Shackleton expedition team in Antarctica thought they had succeeded in finding the South Magnetic Pole. It wasn’t until several years later that the team began to have doubts.

Deborah Byrd

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