Because Jupiter's axis of rotation does not quite line up with its magnetic axis, the moons that orbit the planet feel such a fluctuating magnetic force.
The 16-digit account number stored in your card's magnetic stripe zooms across a leased phone line to the merchant's bank, zips under the Pacific to Visa's data center outside Tokyo and rides the Visa network to the data center of your issuing bank in Delaware.
GoalRef has been developed by German research institute Fraunhofer and involves using magnetic strips inside the ball to detect whether or not it has crossed the goal line.