Citizen Scientist

HOMEBREW

MAGNETOMETER

BUILD A TORSION BALANCE TO MEASURE TINY CHANGES IN THE EARTH’S MAGNETIC FIELD. By Dr. Shawn

M OST OF US ONLY THINK ABOUT THE rotation with a torque (a twisting force) that grows Earth’s magnetism when we need to find as the fiber twists, until it just balances the torque our way in the wilderness. When you look at created by the applied force. The resulting angle of a compass, the Earth’s magnetic field appears to deflection, which is found by bouncing a light beam be a steady guide. But in reality, the magnetic field off a tiny mirror attached to the filament, is propor-fluctuates in response to all sorts of aetheric influ- tional to the force under study. With the beam from ences, some of which come from beyond our world. a laser pointer and a match-head-size mirror, you

For example, the sun boils off a steady stream of can, in principle, resolve deflections as small as one electrons and protons into outer space, and when- ten-millionth of a degree. ever a large solar prominence erupts from the Most torsion balances that you’ll find in profes-surface that’s facing us, a hot torrent of charged sional laboratories use fine quartz fibers, which are particles rushes outward and eventually slams into incredibly strong and insensitive to changes in our cold and relatively quiescent ionosphere. The humidity and temperature. Sadly, quartz fibers are collision between these two wispy plasmas sets difficult for ordinary mortals to come by. But nylon into motion turbulent oceans of electric currents fibers work almost as well as quartz and can be thousands of miles across, which, in turn, create easily extracted from any soft nylon cord. undulating magnetic fields that stretch down through the atmosphere to reach us here on the ground.

Although huge in scale, these magnetic fields are rarely more than a percent of the strength of the Earth’s home magnetic field. Therefore, although these effects are quite common and last from minutes to hours, the magnetic disturbances are notoriously difficult to detect.

Until now, the high cost of tracking these signals meant that professionals had exclusive access to the field. However, anyone can now easily study these magnetic micro-pulsations by building the remarkable magnetometer described here. The simple device requires less than $50 worth of parts and can be built in an afternoon. Yet it can easily capture truly tiny distortions in the Earth’s magnetic field, as well as the dramatic effects of a magnetic storm high in the ionosphere.

The magnetometer uses one of the most sensitive instruments in science — a torsion balance. It measures a force by seeing how far it can be made to twist a fine filament. The thread gently resists

BUILDING THE SENSOR If you want to use carbon fiber, check your local hobby stores; I prefer nylon because it’s much easier to get. To use nylon, start with silky, multi-filamented nylon cord — which you can purchase at any hardware, craft, or boating store — and cut one cord

YOU WILL NEED:

Multi-filamented soft nylon cord 5-minute epoxy

Small piece of aluminized Mylar At least 5mm thick

Spring pin (clothespin) Clear plastic DVD cases ( 2) Penny, minted prior to 1982 Sheet of corrugated cardboard or particleboard Rare-earth magnets ( 2 packages)

RadioShack part #64-1895 Doughnut-shaped magnets ( 4)

RadioShack part #64-1888 Laser pointer

44 Make: Volume 08