This is a photo of my dirt cheap bookshelf magnetometer. The white honey bucket ( drawing, 4 kb )contains a suspended bar magnet with two magnetoresistive components on the outside for measuring the twisting of the magnet in the earths magnetic field. Only one OP-AMP is needed to drive the 1 mA f.s. paper and ink recorder. At the time of taking the photo, the earth magnetic field was in a steady, peaceful state, but during a magnetic storm the recorder pen will traverse from end to end on the scale ( 1 hr/div ). A simple differentiator circuit is all thas is needed to detect potential Aurora Borealis.Here you may find an event (182 kb) coincidental with VHF detected Aurora commencing at around 2230 UTC on June 18th, 1992 (scanned image from stripchart archive, 09.08.2011/OH2AUE)