Gravitational variations across Australia. Credit: Christian Hirt et al.

Keen weight-watchers might notice that standing on a set of scales in Tasmania produces a slightly higher reading than in Queensland.

That’s because the Earth isn’t perfectly spherical, so gravity varies ever so slightly around the world.

An Australian-German research team recently combined gravity measurements with satellite data and small-scale topographical models to find that gravity varies by about 0.7%: about 40% larger than previously expected.

That means a 100kg person weighs 700g more near the North Pole, where gravity is 9.83ms-2, than at Peru’s Nevado Huascaran summit, where gravity is 9.76ms-2.

The same person would weigh 200g more in Tasmania than Queensland, where gravity is 9.78ms-2 and 9.805ms-2 respectively.

“Your weight is largest in Tasmania and smallest in NT/Queensland,” Curtin University researcher Christian Hirt, who led the research, told Business Insider.

“This reflects the dominating effect of Earth’s flattening on the gravity field: Earth’s gravity is generally largest near the poles and smallest in equatorial regions, and experiences a further decreases as you go higher [for example, in mountainous regions].

“[Gravity] varies because Earth rotates, the flattening of Earth, and because the mass-distribution is not homogeneous – think about valleys and mountains that makes Earth deviate from a perfect sphere or ellipsoid, or ore-bodies with higher mass-density than the surrounding masses.”

Gravitational variations, with red denoting where gravity is largest.

Credit: WA Centre for Geodesy

Hirt said the maps were created with the help of the government-supported iVEC supercomputing facility in Western Australia, and were more detailed than previously available maps because they accounted for small-scale topographical features like Ayers Rock.

Researchers expect the maps to be used by civil engineers to help position canals, bridges and tunnels, and miners who could analyse the data to find target areas for mineral exploration.

Hirt said they had no plans to commercialise the maps and data, which are freely available online.

The study was supported by the Australian Research Council; a report was published in the journal Geophysical Research Letters late last month.

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